Bluetongue sheep bluetongue biomaterial. Bluetongue bluetongue (or bluetongue) belongs to a group of exotic, especially dangerous diseases of sheep and domestic and wild ruminants, such as large
Sheep bluetongue (blue tongue) is a non-contagious viral disease of sheep, less commonly of cattle, occurring in the form of an epizootic or enzootic, which is transmitted by blood-sucking insects, mainly midges. The disease in sheep is characterized by fever, ulcerative inflammation of the mucous membranes of the mouth and nasal cavity, swelling of the tongue, swelling of the facial part of the head, pododermatitis and degeneration of muscle fibers.
The BTV virus is able to penetrate the placenta, which leads to various consequences: mummification of embryos, impaired fetal development, and the birth of non-viable lambs. More than 25 serotypes of the virus are known. Many of them can circulate simultaneously. During simultaneous infection with different serotypes of the virus and even different strains of the same serotype, genetic recombination can occur. Antigenic shift is the result of reassortment of genome segments during mixed infection.
Sheep that have recovered from the disease acquire long-term, possibly lifelong, immunity to the type of virus that caused the disease. Complement-fixing and virus-neutralizing antibodies accumulate in the blood and are passed on to the offspring through colostrum. Lambs born from immune sheep remain immune to the disease for 3 months. In sheep that have recovered from the disease, neutralizing antibodies reach their maximum titer by the 30th day and persist for at least a year. CSA appear after 10 days, accumulate maximally after 30 days and remain in high titer for several months after the onset of the disease. Cellular immunity factors play an important role in stopping virus carriage in sheep. A correlation has been noted between the intensity of cellular immunity reactions and the resistance of sheep to challenge infection.
For specific prevention of TB, live and inactivated vaccines are used. When immunizing sheep, live mono- and polyvalent vaccines were widely used, the virus for which was attenuated by serial passages in chicken embryos at a low temperature (33.5°C). The vaccine was successfully used to eliminate epizootics in Portugal and Spain. The antigenic spectrum of the polyvaccine was changed depending on the antigenic characteristics of the circulating virus strains. In South Africa, a vaccine was prepared from 14 antigenically different types of virus. Later, virus strains attenuated in EC were propagated in primary cultures of lamb kidney cells and cattle embryos. Live vaccines are administered to sheep once subcutaneously. Immunity occurs after 10 days and lasts for at least 1 year. However, due to the high reactogenicity of live vaccines, reversion of the virulence of attenuated strains in the body of carriers and the possible emergence of recombinant strains (gene reassortment), especially in the case of polyvaccines, preference began to be given to inactivated vaccines. A safe, highly immunogenic vaccine against BTV was first developed in the former USSR. For this purpose, optimize
The technology for the industrial production of the drug has been developed, methods for controlling the vaccine have been developed, and the conditions for its practical use have been determined.
Particular attention was paid to the development of an industrial method for obtaining high-quality raw materials, a reliable, gentle method for inactivating the virus and obtaining an immunogenic drug. The most technologically advanced and productive (7-8 lg TCD50/ml) method of obtaining viral raw materials turned out to be growing the BTV virus in a suspension of BHK-21 cells. Formalin, DEI and gamma rays were compared as inactivating agents. To control the completeness of virus inactivation, three methods were used: passages of the inactivated drug in PN cell culture; blood passages of vaccinated sheep on non-immune lambs, which were then examined for the presence of virus-neutralizing and complement-fixing antibodies and immunity. All series of inactivated vaccine (0.06% DEI, 37°C, 72 hours) were free from infectious BTV virus. The immunogenicity of the vaccine was determined in sheep by the method of control infection 21-30 days after vaccination and by the VNA titer.
The antigenic and immunogenic properties of the vaccine were significantly increased in the presence of an adjuvant. The sorbed vaccine with GOA 3 mg/ml, saponin 1 mg/ml was not inferior in effectiveness to the emulsified preparation. Titration of nine series of the vaccine in sheep showed that ImD50 in all cases was less than 0.5 ml. Lambs 2-2.5 months of age acquired pronounced immunity only after a double injection of the vaccine. Lambs 4-5 months of age acquired pronounced immunity after a single vaccination.
At 2-6°C the vaccine retained its immunogenic properties for 21-24 months, and at room temperature (20-25°C) for 12 months. (observation period).
The inactivated vaccine at a dose of 2 ml caused pronounced immunity lasting at least 12 months in vaccinated sheep. (observation period). Virus-neutralizing antibodies were detected in the blood of these animals (mainly in dilutions of 1:8 - 1:16), which remained at the same level throughout the year (observation period). No complement-fixing antibodies were detected in these animals, which makes it possible to distinguish sick sheep from vaccinated ones. An inactivated emulsified vaccine against four serotypes of the virus, when administered to sheep in a single dose of 5 ml, created immunity lasting at least 9 months.
According to other authors, complete inactivation of the virus occurred in the presence of 0.02 M DEI at 37°C after 42 hours. The inactivated virus did not cause the formation of any antibodies in sheep; after the addition of an adjuvant, precipitating, less often complement-fixing, but not neutralizing antibodies were formed. Sheep vaccinated with the adjuvant drug did not develop viremia after challenge, indicating the predominant development of cellular immunity after vaccination.
An inactivated emulsified vaccine against two serotypes produced antibodies and provided protection in sheep when challenged with homologous virulent viruses under experimental conditions.
In BTV virus preparations treated with gamma rays at a dose of 60G, residual infectious virus was detected when tested on sheep, but not in cell culture or white mice. No virus was detected in the preparation inactivated by gamma rays at a dose of 100G. This drug induced immunity in sheep and the formation of precipitating and VL antibodies, but did not protect against viremia after challenge. There is a report of obtaining a highly active vaccine, the virus in which was inactivated with platinum salts.
Preventive vaccinations have proven themselves in many countries. However, this applies mainly to live vaccines, since inactivated vaccines have not been widely used.
Bluetongue of sheep, BLO (face disease, gangrenous rhinitis, pseudofoot-and-mouth disease, bluetongue, bluetongue) is a vector-borne disease of ruminants, characterized by fever, inflammatory-necrotic changes in the mucous membrane of the oral cavity and forestomach, vascular system and skeletal muscles
Etiology.
The causative agent of the disease is an RNA virus from the reovirus group.
Epizootology. BWB is distributed in the south, east and northeast of the African continent, in Palestine, Syria, Turkey, Portugal, Spain, Pakistan, India, USA, Peru, Chile and Cyprus. Sheep are susceptible to the virus, especially young animals aged 6 months to a year. Sheep of European breeds are more sensitive than animals of African and Asian breeds. Cattle, buffaloes and wild ruminants can be carriers for a long time.
The pathogen is transmitted by blood-sucking insects (midges, mosquitoes). The disease is usually recorded during the period of active flight of blood-sucking insects (summer-autumn) in places of their mass habitat, near rivers, reservoirs and ponds.
Symptoms of the disease. The disease is acute, subacute and abortive. In acute cases, fever (40.5-42 °C), hyperemia of the mucous membrane of the oral and nasal cavities, hemorrhages, erosions and ulcers on the mucous membrane of the lips, tongue, gums, cheeks, increased salivation (wet mouth), watery with transition to mucous membranes are noted. purulent discharge from the nose, swelling of the eyelids, nostrils, lips, submandibular space, neck and chest, swelling and purplish-blue coloration of the tongue, sometimes its prolapse through a toothless faucet, bad breath, diarrhea. Lameness (inflammation of the corolla) is often observed in sheep that have recovered from the disease. , curvature of the neck and hair loss. In subacute cases, severe exhaustion, weakness and slow recovery of sheep are noted, and in abortive cases, a short-term increase in temperature and rapidly passing hyperemia of the oral mucosa
Pathological changes. The corpses are exhausted. The subcutaneous tissue of the facial part of the head is swollen. The mucous membrane of the lips, tongue and gums is cyanotic and ulcerated. Foci of necrosis of various sizes and shapes are localized in the corners of the lips, on the inner surface of the lower lip, on the back, body and tip of the tongue. Skeletal muscles in the chest, back, neck and limbs are swollen, with pinpoint-striated hemorrhages. Lymph nodes (retropharyngeal and submandibular) are enlarged, swollen and hemorrhagic. Pulmonary edema, catarrhal, fibrinous and aspirated pneumonia, catarrhal gastroenteritis, hemorrhages in the liver, kidneys and papillary muscles of the heart, in the rumen, abomasum and book are often noted.
Histological changes are found in skeletal muscles, muscles of the tongue and heart, as well as in the organs of the digestive tract. They are characterized in muscle tissue by flask-shaped swelling, homogenization, lumpy disintegration, lysis and necrosis of muscle fibers, severe edema, hemorrhages and lymphoid-gnetiocentral infiltration of connective tissue. In the organs of the digestive tract, inflammation and focal necrosis of the epithelium and the underlying interstitial tissue of the mucous membrane (especially the tongue and lips) are established.
Cytopathology. The virus reproduces well in primary cultures of embryonic kidney cells of sheep, cattle, lamb kidneys, hamsters, bovine testicular cell cultures and causes a pronounced, uniform cytopathic effect, which is characterized by an increase in granularity in the cytoplasm, rounding of cells, pycnosis and nuclear disintegration. Complete cell degeneration occurs in 4-6 days after infection. In cell culture, the virus forms cytoplasmic and intranuclear inclusions.
The diagnosis is made based on the analysis of epizootic, clinical, pathomorphological data and the results of virological studies. When taking into account epizootological data, attention is paid to the type and age of sick animals, time of year, area, presence of vectors, stationarity and non-contagiousness of the disease. Of the clinical signs, fever and damage to the oral cavity are of diagnostic importance.
Detection of necrodystrophic changes in the muscles of the skeleton, tongue and heart, as well as in the mucous membrane of the digestive tract (especially lips and tongue) in combination with severe swelling, hemorrhages and lymphoid-histiocytic infiltration of the interstitial connective tissue allows us to make a presumptive diagnosis of bluetongue in sheep
For the final diagnosis, the virus is isolated, identified and a bioassay is performed.
Differential diagnosis. Bluetongue in sheep must be distinguished from foot-and-mouth disease, smallpox, ecthyma, Nairobi disease, Rift Valley fever, necrobacteriosis and lamb disease.
Foot-and-mouth disease in sheep is characterized by aphthous lesions of the skin of the extremities, especially in the area of the corolla, the walls of the interhoof cleft, and crumbs. Sheep pox affects hairless and thin areas of skin (around the eyes and nose, lips, cheeks, udder, scrotum and inner thighs and tail). Histological examination reveals elementary particles of the smallpox virus in the epithelial cells of the affected areas (papules and pustules). Sheep ecthyma is characterized by a nodular form of inflammation of the skin and mucous membranes. Dark brown nodules are most often localized along the edges of the upper and lower lips, in the corners of the mouth, on the nasal planum, near the nostrils, less often on the mucous membrane of the cheeks, tongue, palate, pharynx, larynx and trachea, clearly protrude above the surface of the skin and resemble warty growths in appearance. A diagnostic test is the detection of eosinophilic inclusions in the cytoplasm of degenerating epithelial skin cells.
Nairobi disease occurs with symptoms of hemorrhagic diathesis and gastroenteritis. The large intestine is especially severely affected, on the mucous membrane of which striped hemorrhages are constantly found.
The pathognomonic sign of Rift Valley fever is necrodystrophic liver damage and the formation of acidophilic intranuclear inclusions (Rubart's bodies) in hepatocytes. Necrobacteriosis mainly affects the extremities. The pathological process develops in the tissues of the interhoof wall, on the corolla, crumbs, sole and is characterized by putrefactive decay of the subcutaneous tissue, tendons, ligaments and joint capsules. The causative agent of the disease, Vas, is found in the affected tissues. pesgorosht. White muscle disease, in contrast to CLO, mainly affects lambs immediately after birth and before they are weaned from the uterus, that is, up to 4-5 months. In addition to characteristic changes in the myocardium (necrosis), with this disease, symmetrical waxy necrosis is found in the muscles of the croup, hips, back, and shoulder girdle.
INSTRUCTIONSon measures to prevent and eliminate infectious diseases
GENERAL PROVISIONS
1.2. The causative agent of the disease is an RNA virus belonging to the Orbivirus genus of the Reoviride family, which has 24 serotypes. The virus is not resistant to environmental factors.
1.3. The source of the infectious agent is patients and virus carriers among ruminants. The main route of transmission of the pathogen is transmissible - through the bites of midges, mainly of the genus Gulicoides. In this regard, the disease is seasonal and is associated with the breeding and biological activity of insects. Additional routes of transmission are through sperm and in utero.
1.4. The diagnosis of BLO is made on the basis of clinical, epizootological, pathomorphological data and laboratory test results.
1.4.1. For laboratory studies - isolation of the virus and its serotyping - blood samples are sent from 3-5 sick animals, which are preserved in Edington's liquid (50 ml of glycerin, 4 g of phenol, 5 g of oxalic acid and distilled water - up to 100 ml) in a ratio of 1: 1; and from 3-5 dead or forcedly killed animals, pieces of the spleen and lymph nodes, and for retrospective diagnosis, paired blood serum samples taken from 5-10 animals with an interval of 10-14 days are sent. Samples of pathological material are placed in a sterile hermetically sealed container, then in a thermos with ice and delivered to the laboratory by express delivery.
1.4.2. Research is carried out in republican, regional, regional veterinary laboratories or at the All-Russian Research Institute of Veterinary Virology and Microbiology (VNIIVViM, 601120 Pokrov, Vladimir Region), in accordance with guidelines for laboratory diagnostics of TB. In primary foci of the disease, the final diagnosis is based on the isolation of the virus from sick animals and its identification, in secondary or stationary foci - on the identification of seropositive animals.
2. MEASURES TO PREVENT THE INTRODUCTION OF THE PAGUENT AND PROFESSIONAL
LACTICS OF INFECTIOUS BLUETOOTH FEVER OF SHEEP
2.1. The basis for the prevention of BTB is the prevention of the introduction of the pathogen from unaffected countries by infected animals, sperm obtained from them, embryos or carriers, as well as vaccination of sheep and goats in the regions of the Russian Federation bordering countries unaffected by BW (if the disease appears there).
2.2. To prevent the occurrence of BW, the owner of animals (legal or individual) in accordance with the Law of the Russian Federation “On Veterinary Medicine” is obliged to:
2.2.1. Provide systematic veterinary monitoring of the condition of the sheep, goats and cattle;
2.2.2. To stock flocks (farms) with animals from farms in other regions that are free from CL;
2.2.3. All new ruminant animals entering the farm must be quarantined for 30 days under strict veterinary control, after which, with the permission of the veterinarian, the animals must be transferred to a general group;
2.2.4. If clinically sick and seropositive animals are detected, the entire group of imported animals is slaughtered. The sanitary assessment of the slaughter products of such animals is carried out according to clause 4.2.;
2.2.5. Constantly maintain pastures, watering areas, livestock buildings in proper veterinary and sanitary condition, as well as carry out other measures provided for by veterinary and sanitary rules for the protection of farms from the introduction of pathogens of infectious animal diseases;
2.2.6. Livestock raw materials used for breeding and consumer purposes (sperm, blood, embryos, etc.) must be obtained from healthy seronegative donors, and the containers in which they are delivered (bales of wool, etc.) must not contain live carriers;
2.3. If BW occurs in a neighboring country and there is an immediate threat of the infection being introduced into the territory of the Russian Federation, the state veterinary service authorities of the border regions create emergency anti-epizootic commissions to combat BW, which carry out:
2.3.1. Explanatory work among owners of ruminant animals, as well as managers of owners of processing enterprises, trade and procurement organizations about the dangers and measures to prevent the introduction of the disease agent into the country; the population must be prepared to consciously participate in activities against BWB;
2.3.2. Serological control by selective assessment of the presence of antibodies among the ruminant population in the threatened region (with a radius of at least 20 km) against the BTV pathogen (clause 1.4.2.). The assessment is carried out using the compliment binding reaction (CBR) or enzyme-linked immunosorbent assay (ELISA) by examining blood sera taken from 0.5-1% of the population of small ruminants and 7-10% of the population of large ruminants;
2.3.3. Measures to combat blood-sucking arthropods in pastures and livestock buildings (clause 4.1.4.).
3. MEASURES IN THE EVENT OF SUSPECTED INFECTIOUS DISEASE
Bluetongue of SHEEP
3.1. If there is a suspicion of a BTB disease, the veterinarian serving the farm notifies the chief veterinarian of the area and, before his arrival, together with the animal owners, takes measures to exclude the possibility of spreading the disease:
3.1.1. Isolate all sick and suspected animals, organize their feeding and watering in specially designated areas that exclude contact with other flocks;
3.1.2. Pathological material is selected from the most recent corpses and sent for laboratory testing according to clause 1.4.1. and 1.4.2. The locations of animal corpses are thoroughly disinfected, and the corpses are destroyed according to clause 4.1.10.
3.1.3. Animals, regardless of the time of year, are kept in stalls or in isolated walking yards and treated with repellents and insecticides;
3.1.4. In conditions of transhumance livestock farming, a zone free from susceptible animals is created around the disadvantaged herd within a radius of 7-10 km.
3.1.5. Once every 7 days, equipment and bedding in the territory of a disadvantaged group of animals are disinfected;
3.1.6. By decision of the district administration, until the diagnosis is clarified, production connections of a farm suspected of trouble with successful farms and farms, as well as any movements of ruminant animals within the farm, the import into and export of animals, wool, raw hides, and sperm of producers, are stopped.
3.2. The chief veterinarian of the district, upon arrival at a troubled point, is obliged to:
3.2.1. Immediately take urgent measures to clarify the epizootic situation and make a diagnosis (clause 1.4.),
3.2.2. Organize a clinical examination and thermometry of all animals suspected of disease and infection, followed by the separation of sick and feverish animals into a separate group according to clause 3.1.17.
3.2.3. In case of suspicion of BTB disease in wild ruminants (clause 1.3.), organizes their selective shooting, the pathological material collected from them is sent to the laboratory for diagnostic studies (clause 1.4.),
3.2.4. Organize and carefully monitor the implementation of veterinary and sanitary measures to ensure the prevention of further spread of the disease (clauses 5.3-5.5);
3.2.5. Inform the higher veterinary service of the region about the occurrence of the disease and the epizootic situation.
4. MEASURES TO ELIMINATE INFECTIOUS
Bluetongue of SHEEP
4.1. Upon receipt of confirmation of the diagnosis of BWB, the district administration, upon the recommendation of the chief veterinarian of the district, declares the farm (farm) or pasture area where the unfavorable flock (herd) was grazing, in accordance with the established procedure, as unfavorable. The following restrictive measures are taken for this disease:
4.1.1. The export of domestic and wild ruminant animals to other farms for breeding and consumption purposes, slaughter products and raw materials of animal origin (milk, wool, skins), as well as semen, canned blood and blood serum of ruminants is prohibited;
4.1.2. Transit passage of all types of transport through the territory of a disadvantaged point is prohibited. Detour routes must be organized for the passage of vehicles;
4.1.3. Animals that are sick and suspected of having TB disease are placed in a separate group and the measures according to clause 3.1 are continued;
4.1.4. They organize the fight against insects that carry the disease in accordance with the current “Guidelines for combating midges and protecting animals from their attacks.” All transport leaving the boundaries of the unfavorable economy (zone) is subject to mandatory treatment with insecticides: 1% aqueous emulsions of trichlorometaphos-3, karbofos; it is possible to use ready-made pharmaceutical forms of pyrethroids (Decis, Permethrin, etc.);
4.1.5. During the active summer period, insects, sheep, goats and, if possible, other ruminants are kept in elevated areas and systematically treated with repellents and insecticides;
4.1.6. Premises for animals (sheds, sheds, shelters, etc.), farm areas, slaughter areas, livestock equipment, special clothing and transport are subjected to disinfection and disinfestation. Disinfection is carried out with a 2% solution of formaldehyde, a 4% hot solution of caustic soda, a solution of two-thirds calcium hypochlorite salt (DTSGK) or bleach containing at least 3% active chlorine at the rate of 1 l/m2 and an exposure of 3 hours;
4.1.7. Constant veterinary monitoring of animals from disadvantaged flocks (herds) is established during the summer grazing period. Animals identified during a veterinary examination or suspected of having TB disease are subject to slaughter according to clause 4.2.;
4.1.8. In the event of the appearance of BWB in areas where the disease has not been recorded for 3 or more years, or on small farms, it is necessary to slaughter all sheep (goats) of the affected flock or farm.
4.1.9. All clinically healthy sheep, goats and cattle are annually vaccinated against BTV with live vaccines (of the appropriate serotype) or inactivated (prepared from a strain of the pathogen isolated in the outbreak of the disease or from a homologous serotype of the BTV virus) in accordance with the instructions for their use. Vaccinated animals must be under the supervision of veterinary specialists for at least 14 days.
4.1.10. Animal corpses are burned in trenches or specially designated areas, the remains are buried to a depth of at least 1.5 m. Skinning animal corpses is prohibited.
4.2. The slaughter of sheep (goats) is carried out at a specially designated slaughter site or sanitary slaughterhouse (meat processing plant) within the time limits established by the state veterinary inspection service for immediate slaughter, under the supervision of the chief veterinarian of the region. In this case, clinically sick and suspected animals are killed, after a group of animals suspected of infection. After slaughter, disinfection, disinfestation and decontamination of all places where the slaughtered group of animals were located are carried out.
Meat and other products obtained from the slaughter of sick and suspected animals with TB disease are subject to industrial processing or boiling, bringing the temperature in the bulk of the mass to at least 80 0 C for 2 hours. Internal organs, heads and legs of carcasses with degenerative changes in the muscles, hemorrhages in the subcutaneous tissue or signs of emaciation are sent for technical disposal. The release of meat and other slaughter products in raw form is prohibited.
4.3. Wool obtained from sheep from unfavorable flocks is transported from the farm to processing plants, packed in thick fabric, where it is disinfected in accordance with the current “Instructions for the disinfection of raw materials of animal origin and enterprises for their procurement, storage and processing.”
4.4. Skins obtained from animals sick and suspected of having TB disease after their slaughter are neutralized with a 1% formaldehyde solution or a curing mixture containing 83% table salt, 7.5% ammonium chloride and 2% soda ash, followed by folding the skins into piles and aged for at least 10 days.
5. EVENTS IN THE AREA THREATENED BY SKIDS
CAUSE OF DISEASE
5.1. The threatened zone includes territories with farms directly adjacent to a point unfavorable for TB.
5.2. In the threatened zone, restrictive veterinary, sanitary and preventive measures are carried out according to a plan developed by the district veterinary service and approved by the district administration.
5.3. Establish strict veterinary control over all livestock farms and farms, carrying out systematic veterinary monitoring of their condition, and also carry out serological monitoring of BLO (regular monitoring of infection by the accumulation of virus-specific antibodies in the blood of small and large ruminants) through selective sampling and research blood serum samples (clause 2.3.2.).
5.4. Tracking is carried out in the threatened zone to a depth of 20 km from the border of the troubled point. To do this, during the summer midges are found monthly, and in the cold season - quarterly. If seropositive animals are detected in a flock (herd), the entire group of animals is vaccinated with a vaccine against BTV from a homologous serotype of the virus, the pathological material is examined according to clause 1.4. If a clinical, pathological or laboratory diagnosis of BLO is established at this point, it is declared unfavorable for this infection in accordance with Section 4.
5.5. They carry out the fight against insect vectors (clause 4.1.4.). They organize monitoring of the movement of wild animals and do not allow them into the territory of the threatened zone.
6. REMOVING RESTRICTIONS
6.1. The established restrictions under clause 4 in farms (farms) and pasture areas that are unfavorable for TB are canceled in accordance with the established procedure one year after the last case of death or recovery of sick animals. In this case, the following final veterinary and sanitary measures are carried out:
6.1.1. Before lifting restrictions, owners of ruminant animals, under the guidance of specialists from the state veterinary service, are required to carry out cleaning and final disinfection and disinsection of all livestock premises and areas of walking yards and pens where sick animals were located;
6.1.2. Depending on the characteristics of the object being treated, use one of the following disinfectants: hot 4% solution of sodium or potassium hydroxide; hot 3% solution of sulfur-carbol mixture; 20% solution of freshly slaked lime; a clarified solution of bleach or sodium hypochlorite containing at least 3% active chlorine; 2% formaldehyde solution; 40% formalin solution - for the steam-formalin chamber;
6.1.3. Ruminant animals located in an unfavorable point (item 4) are bathed in a 1% creolin emulsion in the warm season, and treated with acaricidal preparations (Ivomek, Butox, etc.) in the cold season;
6.1.4. The chief veterinarian of the district, together with the owner of the animals, checks the completeness of the implementation of veterinary and sanitary measures and draws up an appropriate report.
6.2. The ban on the export of domestic and wild ruminant animals from a previously unfavorable farm under BWL is lifted no earlier than 3 years after the restrictions are lifted. During this period, in a disadvantaged area and a threatened zone, a general vaccination of ruminants against BTV is carried out annually with a vaccine from a homologous serotype or virus isolated in the outbreak of BTV; all vaccinated animals are killed after fattening, and the meat is subjected to industrial processing (section 4.2). The new livestock is made up of sheep imported from prosperous farms. In this case, the importation of animals is carried out during the absence of summer of blood-sucking insects (autumn-winter time) and subject to negative results of testing in the RSC (ELISA) of blood sera of ruminants (goats, sheep, cattle) for the presence of antibodies to the BTV virus. Within 1 year after importation, animals are subjected to random serological examination according to clause 2.3.2.
The instructions were developed by the All-Russian Research Institute of Veterinary Virology and Microbiology.
With the approval of this Instruction, the “Instruction on measures to combat bluetongue in sheep”, approved by the Main Directorate of Internal Affairs of the USSR Ministry of Agriculture on March 27, 1974, becomes invalid.
Bluetongue of sheep(blue tongue) is a non-contagious viral disease of sheep, less commonly of cattle, occurring in the form of an epizootic or enzootic, which is transmitted by blood-sucking insects, mainly midges. The disease in sheep is characterized by fever, ulcerative inflammation of the mucous membranes of the mouth and nasal cavity, swelling of the tongue, swelling of the facial part of the head, pododermatitis and degeneration of muscle fibers.
Bluetongue virus is able to penetrate the placenta, which leads to various consequences: mummification of embryos, impaired fetal development, and the birth of non-viable lambs. More than 25 serotypes of the virus are known. Many of them can circulate simultaneously. During simultaneous infection with different serotypes of the virus and even different strains of the same serotype, genetic recombination can occur. Antigenic shift is the result of reassortment of genome segments during mixed infection.
Recovered sheep acquire long-term, perhaps lifelong, immunity to the type of virus that caused the disease. Complement-fixing and virus-neutralizing antibodies accumulate in the blood and are passed on to the offspring through colostrum. Lambs born from immune sheep remain immune to the disease for 3 months. In sheep that have recovered from the disease, neutralizing antibodies reach their maximum titer by the 30th day and persist for at least a year. CSA appear after 10 days, accumulate maximally after 30 days and remain in high titer for several months after the onset of the disease. Cellular immunity factors play an important role in stopping virus carriage in sheep. A correlation was noted between the intensity of cellular immunity reactions and the resistance of sheep to challenge infection.
For specific prevention of bluetongue in sheep Live and inactivated vaccines are used. When immunizing sheep, live mono- and polyvalent vaccines were widely used, the virus for which was attenuated by serial passages in chicken embryos at a low temperature (33.5°C). The vaccine was successfully used to eliminate epizootics in Portugal and Spain. The antigenic spectrum of the polyvaccine was changed depending on the antigenic characteristics of the circulating virus strains. In South Africa, a vaccine was prepared from 14 antigenically different types of virus. Later, virus strains attenuated in EC were propagated in primary cultures of lamb kidney cells and cattle embryos. Live vaccines are administered to sheep once subcutaneously. Immunity occurs after 10 days and lasts for at least 1 year. However, due to the high reactogenicity of live vaccines, reversion of the virulence of attenuated strains in the body of carriers and the possible emergence of recombinant strains (gene reassortment), especially in the case of polyvaccines, preference began to be given to inactivated vaccines. A safe, highly immunogenic vaccine against BTV was first developed in the former USSR. For this purpose, the technology for industrial production of the drug has been optimized, methods for monitoring the vaccine have been developed, and the conditions for its practical use have been determined.
Particular attention was paid to the development industrial method of production high-quality raw materials, a reliable, gentle method of inactivating the virus and obtaining an immunogenic drug. The most technologically advanced and productive (7-8 lg TCD50/ml) method of obtaining viral raw materials turned out to be growing the BTV virus in a suspension of BHK-21 cells. Formalin, DEI and gamma rays were compared as inactivating agents. To control the completeness of virus inactivation, three methods were used: passages of the inactivated drug in PN cell culture; blood passages of vaccinated sheep on non-immune lambs, which were then examined for the presence of virus-neutralizing and complement-fixing antibodies and immunity. All series of inactivated vaccine (0.06% DEI, 37°C, 72 hours) were free from infectious BTV virus. The immunogenicity of the vaccine was determined in sheep by the method of control infection 21-30 days after vaccination and by the VNA titer.
Antigenic and immunogenic properties of the vaccine significantly increased in the presence of an adjuvant. The sorbed vaccine with GOA 3 mg/ml, saponin 1 mg/ml was not inferior in effectiveness to the emulsified preparation. Titration of nine series of the vaccine in sheep showed that ImD50 in all cases was less than 0.5 ml. Lambs 2-2.5 months of age acquired pronounced immunity only after a double injection of the vaccine. Lambs 4-5 months of age acquired pronounced immunity after a single vaccination.
At 2-6°C the vaccine retained immunogenic properties for 21-24 months, and at room temperature (20-25°C) - 12 months. (observation period).
Inactivated vaccine at a dose of 2 ml caused pronounced immunity lasting at least 12 months in vaccinated sheep. (observation period). Virus-neutralizing antibodies were detected in the blood of these animals (mainly in dilutions of 1:8 - 1:16), which remained at the same level throughout the year (observation period). No complement-fixing antibodies were detected in these animals, which makes it possible to distinguish sick sheep from vaccinated ones. An inactivated emulsified vaccine against four serotypes of the virus, when administered to sheep in a single dose of 5 ml, created immunity lasting at least 9 months.
According to other authors, complete inactivation of the virus occurred in the presence of 0.02 M DEI at 37°C after 42 hours. The inactivated virus did not cause the formation of any antibodies in sheep; after adding an adjuvant, precipitating, less often complement-fixing, but not neutralizing antibodies were formed. Sheep vaccinated with the adjuvant drug did not develop viremia after challenge, indicating the predominant development of cellular immunity after vaccination.
Inactivated emulsified vaccine against two serotypes caused the formation of antibodies and created protection in sheep when infected with homologous virulent viruses under experimental conditions.
In preparations bluetongue virus, treated with gamma rays at a dose of 60G, residual infectious virus was detected when tested in sheep, but not in cell culture or in white mice. No virus was detected in the preparation inactivated by gamma rays at a dose of 100G. This drug induced immunity in sheep and the formation of precipitating and VL antibodies, but did not protect against viremia after challenge. There is a report of obtaining a highly active vaccine, the virus in which was inactivated with platinum salts.
Ministry of Education of the Russian Federation
Moscow State University of Applied Biotechnology
Department of Veterinary and Sanitary Expertise
Coursework
on pathological anatomy of farm animals
on the topic: pathological anatomy
bluetongue in sheep
completed by: 4th year student, 7th group
Kovaleva Marina
Moscow 2006
Economic losses
Pathogen
Epizootological data
Pathogenesis
Clinical symptoms
Diagnostics
Differential diagnosis
Immunity and prevention
Control measures
Conclusion
Definition of disease
Bluetongue (BBL) is a viral transmissible disease of ruminants, characterized by a febrile state, inflammatory and necrotic lesions of the oral cavity (especially the tongue), gastrointestinal tract, coronary epithelium and base of the skin of the hooves, as well as degenerative changes in the skeletal muscles.
Geographical distribution of the disease
In South Africa, K. LO has been known since the 17th century. as a disease of local breeds of sheep, which is often asymptomatic. Only with the import of European breeds of sheep into Africa did the disease become malignant and attract the attention of researchers. The report of the Sheep and Cattle Diseases Commission, dated 1st 76, was the first to report sheep “fever”, which was observed in the Cape Province (South Africa), where merino sheep were imported from Europe. The outbreak of the disease affected almost 30% of the animals and caused high mortality among them. The disease was recognized by swelling of the tissues of the head, redness of the conjunctiva and mucous membranes of the oral and nasal cavities, and damage to the lower extremities.
The first description of CLO was made by Hutcheson (1881), who called the disease “enzootic catarrh.” A more systematic study was carried out in 1902-1905. Spreul, who tried to immunize sheep with simultaneous injections of hyperimmune serum and infected sheep blood. Later (1906) Theiler proved that the disease is caused by an agent found in the blood and serum of sheep, and that this agent can pass through the Berkerfeld filter.
For a long time, it was believed that the disease was limited to the African continent, where, with the development of agriculture, the disease was systematically recorded based on clinical symptoms. However, since 1943 The disease began to be reported outside of Africa. Thus, in 1943, a severe epizootic was observed among sheep in Cyprus, and in the same year - in Palestine and Syria. Since 1944, BTV has been registered in Turkey (in the southern regions), where it caused high mortality among sheep. Tamer (1949) suggests that in Turkey the disease was caused by a particularly highly virulent strain of the virus.
According to the literature, about 40 countries are known in which BWB was registered in different years. In recent years, the disease has been constantly recorded in 18-20 countries in Africa, the Near (Syria, Israel, Turkey), Middle (Pakistan, India) and Far (Japan, inaccurate) East.
In 1956, the disease first appeared in Europe in the south of Portugal, where it clinically manifested itself in sheep and cattle. Soon it was registered in Spain (south and southwest of the country). Since 1948, the disease has been continuously reported in the United States, and in 1968 it appeared in Chile and Peru. In the United States, the disease, described as soremuzzle, first appeared in Texas, where it affected 29,800,000 sheep. Five years later, in California, where large losses of sheep were observed, the same virus was isolated (McGower, 1952). In the period from 1952 to 1964. The virus was isolated in 16 US states.
From the materials of the 36th session of the International Bureau of Epizootics it is clear that in 1967 in South Africa, the disease affected 37,900,000 sheep and 5,394,000 goats; in Kenya - 711,000 and 6,400,000, in Uganda - 711,000 and 1,960,000 - in Rhodesia - 102,000 and 621,000; in Egypt - 1,930,000 and 790,000; in Cyprus - 340,000 and 250,000; - in Israel - 300,000 and 300,000, respectively; in the USA - 26,452,000 sheep.
In 1968, the disease was registered in Sudan, Nigeria, Cameroon, Ethiopia, Kenya, Zaire, Zambia, Angola, Botswana, South Africa, Egypt, Lesotho, USA, Cairo, Israel, Pakistan, and India.
Economic losses
They are huge and consist of the death of animals, loss of their productivity (wool, meat) due to long recovery, costs of vaccination and diagnostics.
Sheep mortality is 5-10% (USA, Japan), but particularly virulent strains cause up to 85% mortality (Cyprus, Portugal, Israel). In stationary outbreaks, the mortality rate is 0.5-1.0%. Among imported sheep, the morbidity rate is 20.5%, mortality is 1.4% (Israel).
Some foreign researchers (Alexander, 1948; Howell, 1963; Haig, 1965) characterize BLO as a very dangerous infection, the elimination of which is very difficult due to the presence of natural focality and some biological properties of the virus. American scientist Kennedy (1968) considers CL “more malignant than foot and mouth disease,
exotic disease of domestic animals." Scientists in Australia (Grant et al., 1967; Gardiner et al., 1968) and Canada (Ruckerbauer et al., 1967) have expressed great concern about the possibility of the emergence of CLOs.
Pathogen
Morphology, chemical composition, taxonomic position. In 1948, Paulson made the first attempt to determine the size of the virion. Using ultracentrifugation and ultrafiltration methods of blood and spleen suspension, he found that the size of the virion was 108-133 nm. In 1958, Kitts showed that the BTV virus is precipitated by centrifugation for 60 minutes at 30 thousand rpm. In this case, the so-called soluble (complement-fixing) antigen remains in the supernatant, the particle size of which is approximately 8 nm.
The morphology of TB virus virions has been studied by many authors, but received relatively contradictory results. Ele and Vervoord (1969) worked with highly purified virus preparations and therefore their data can be considered the most reliable. They found that most viral particles, of the same size, have an average diameter of 53.8 nm and lack an envelope. The authors came to the conclusion that in terms of morphology and a number of other properties, the BTV virus is not similar to reoviruses. Vervoord and Huysmoens, who conducted a comparative study of reovirus, BTV and AHS viruses, came to a similar conclusion.
BTV virus virions contain 2-stranded RNA, consisting of 10 fragments, the molecular weight of which ranges from 0.28 to 2.7 million daltons. The virion has a single-layer capsid consisting of 32 capsomeres arranged in 5:3:2 symmetry and forming an icosahedron. Some virions have an extracapsid layer, which masks the capsomeres and increases the diameter of the virions to 65-77 nm (Lekatsos and Gorman, 1977). It is believed that these pseudoenvelopes are acquired by viral particles upon exiting the cell by capturing part of the cell membrane. Perhaps pseudoenvelopes protect viral particles from the neutralizing effect of antibodies, which explains the simultaneous circulation of virus and antibodies in the blood (J. Brown et al, 1970).
The BLO virus contains 20% RNA and 80% protein, has K = 650S and a density of 1.38. There are at least 7 types of protein with different molecular weights. (from 32 to 155 thousand).
Based on the morphology of virions, physicochemical and antigenic properties, in 1975 the Commission on the Nomenclature of Viruses formed the genus Orbivirus, which included viruses of BTV, African horse sickness, Colorado tick fever, epizootic hemorrhagic disease of deer, etc. The genus Orbivirus is included in the family. Reoviridae.
On top, complete bluetongue virus particles from a sugar gradient, negative contrast with phosphotungstic acid. Visible diffuse appearance of virions (68 nm in diameter)
Below are bluetongue virus particles from a CsCl gradient, pH 6.0. Surface details shown. the inner capsid (diameter 55 nm) consists of a single layer of regularly packed morphological units or capsomeres (÷125,000)
Sustainability. The virus is resistant to lipid solvents: ether, chloroform, sodium deoxycholate. It is sensitive to trypsin and an acidic environment (pH 6.0 inactivates within 1 minute at 37°). The virus is quite resistant to alkaline environments, stable at pH 6.5-8.0. In lamb and beef meat, when it ripens, when its pH is 5.6-6.3, the virus is inactivated. However, in lamb carcasses stored at +4° (pH 6.3), the virus persists for 30 days (Aries, 1964).
In the blood, the virus retains its activity even after it has decayed (Theiler, 1906); Blood mixed with Edington's liquid (potassium oxalate - 5.0, carbolic acid - 5.0, glycerin - 500.0, distilled water - 500.0) remained infectious at room temperature for 25 years. (However, there are indications from Arab authors that when sent to the Onderstepurt laboratory, such blood lost its infectious properties). According to Howell (1963), blood, pieces of spleen and lymph nodes taken into Edington's fluid remain infective for several years.
The infectivity of serum is almost the same as that of whole blood. In a virus-containing culture liquid, the virus is best preserved at a pH of 7.2-7.4 and a temperature of + 2 + 4°. The virus is not heat resistant. Thus, at +60° the virus is completely inactivated within 30 minutes (while infectivity drops sharply within the first 5 minutes). The thermal inactivation curve of the virus at 37, 46 and 56° is two-component, which indicates the heterotenity of the viral population. Freezing a virus-containing culture liquid without a stabilizer to -20° leads to a loss of its infectivity. The same thing happens when quickly frozen in a mixture of dry ice and alcohol. According to Howell (1967), 50% buffered lactose peptone turned out to be the best virus stabilizer when stored at -20° and -70°. In this case, the virus was better preserved at -70° than at -20°.
In virus-containing materials freeze-dried with stabilizers, the virus was well preserved at -20° and +4° for a number of years (Howell, 1967).
A brain suspension on a nutrient medium preserved the virus for 5 years, and an infected chicken embryo at +6°C preserved it for up to 7 years. A 3% formaldehyde solution inactivates the virus within 48-72 hours, a 3% sodium hydroxide solution and 70°C ethyl alcohol - for 5 minutes.
The virus does not agglutinate red blood cells of sheep, cattle, rooster, goose, guinea pig, rabbit, and mouse.
Antigenic properties. Neitz in 1948, in experiments with cross-immunization of sheep, first established the antigenic multiplicity of the BTV virus. This was then confirmed in vitro in a neutralization reaction. By cross-infecting sheep, it was shown that each type of virus confers strong and long-lasting immunity against itself, but only an intermittent and weak degree of protection against other types. Currently, 16 types of virus are known, differing in RN, but all of them are indistinguishable (have a common antigen) in RSC, RDP and RIF. In animals that have recovered from the disease, neutralizing, complement-binding and precipitating antibodies are formed. Repeated injections of a homologous strain into sheep do not increase the intensity of immunity and do not increase the spectrum of polyvalency of immunity. It has been established that several types of virus can simultaneously circulate in the same geographic area (Du Toit and Howell, 1962). Thus, Howell (1967) reported that within 29 days, 9 immunologically different types of BTV virus were isolated and identified on 2 adjacent farms. In the United States, at least 5-6 types of virus have been identified to be circulating simultaneously. Several types are installed within Egypt, Israel and other countries. The multitype of the BTV virus complicates the diagnosis and prevention of the disease.
Whether there is a change in the type of virus is unknown. But strains are known that are highly stable. Thus, the 4th type strain was isolated by Theiler in 1905 in South Africa, as well as in 1951 and 1964. in Israel - they turned out to be stable. Antigenically identical strains have been isolated in different geographic areas (strain type 3 in Cyprus in 1949, in South Africa and California in 1953, and in Portugal in 1956).
Spectrum of pathogenicity. Sheep are the most sensitive domestic animals to the BTV virus. It has been shown that European breeds are more sensitive than African and Asian breeds, such as Black Persian and Karakul (Howell, 1963).
Significant fluctuations in the individual sensitivity of sheep of the same breed have been noted. Differences in individual sensitivity and variations in the virulence of virus strains make it difficult to predict the severity of an epizootic in natural conditions. Deterioration of living conditions, high solar radiation and other factors can lead to the fact that a low-virulent strain can cause high mortality and large economic losses.
Lambs born from non-immunized dams are very susceptible to the virus. If a new antigenic type of virus enters an enzootic area, the diseases it causes are usually less severe than when the virus enters a prosperous area where the entire animal population is susceptible to the virus. Among such animals, an epizootic can cause large losses and, given the right conditions, spreads very quickly, as was the case in 1956 in Spain and Portugal.
Cattle are sensitive to the BTV virus. In 1934, Becker and others described the clinic and isolated the virus from cattle under natural conditions. Clinically, the disease resembled foot-and-mouth disease (farmers called it pseudo-foot-and-mouth disease). In most cases, the course of the disease was subclinical.
In 1937, De Kock and others in South Africa isolated the virus from cattle that showed no clinical signs of disease. In almost all cases of TB outbreaks among sheep outside Africa, the same clinical manifestations as in sheep were simultaneously observed in cattle (in Israel - in 1951, in Portugal and Spain - in 1956, in the USA - in 1960).
However, under experimental conditions, no one has yet been able to cause clinical manifestations of the disease in cattle using any route of introduction of the virus. Only a few authors noted a short-term rise in body temperature and sometimes a drop in appetite.
Goats are sensitive to the BTV virus. Some farmers observed the disease in goats during natural outbreaks of BBT in sheep (Spreuli, 1905; Hards and Price, 1952). Experimentally, it was also possible to induce the disease in goats. Zebu, buffalo, antelope, white-tailed deer, elk, bighorn sheep, Barbary sheep, moose and other ruminants are also susceptible to the BTV virus.
In 1969, Trainer (S1.PA), in a study of 314 blood sera of wild ruminants (not deer), found the presence of precipitating antibodies to the BTV virus in 27% (elk, moose, bighorn and Barbary sheep).
Of 698 sera from various species of wild deer, 55% reacted positively to BW in the RDP, including white-tailed, black-tailed and mule deer.
Responding wild ruminants were found in geographic areas where BTV has been reported among domestic animals. But there have been cases of unexpected detection of positive wild deer and moose in Ontario, where BTV has not been reported in domestic animals.
Under experimental conditions (Vozdinch, Trashir, 1908) it was established; that white-tailed deer and their fawns are highly susceptible to the BTV virus. All fawns under the age of 1 year (7 heads) died on the 6-8th day after infection. One of the 3 adult deer died. The virus was isolated from the spleen. liver, kidneys, prescapular lymph nodes, blood, pleural fluid, urine. The duration of viremia in deer is 10 days after infection. Some wild ruminants have been found to carry the virus for different durations (Netz, 1966, Vozdnich, 1968).
The BTV virus was isolated from two species of rodents, Rabdomis pumilo and Otomys irreratus.
Cultivation. In 1940, Alexander et al. for the first time reported the ability of the BTV virus to multiply in chicken embryos that died due to various routes of infection. Most often, 6-8 day old embryos are infected into the yolk sac or 9-11 day old embryos into the vein. In 1947, Alexander found that the greatest accumulation of the virus occurs when an infected chicken embryo is incubated at 33.5° in the period from 36 to 72 hours after infection. The virus titer reaches 105.6 - 108 ELD5 o/ml, depending on the strain of the virus In infected chicken embryos, there is congestion of blood vessels, hemorrhages, the embryo acquires a cherry color. Microscopically, in such embryos, CPD is observed in the cells of the muscles, liver, kidneys, brain, and blood vessels.
Alexander, Haig et al. (1947) found that serial passages of the BTV virus on chicken embryos lead to its attenuation in sheep. The relative ease and consistency of this process has made it possible to obtain live vaccines that are widely used in many countries.
White mice were sensitive to the BLO virus after intracerebral infection. In adult mice, the infection is asymptomatic, and the virus accumulates in the brain in low titers. When mice are infected up to 10-13 days of age, 100% death occurs, and the virus accumulates in the brain at titers of 106 ° -108 ° MLD 5o/ml. The most sensitive are 1-4 day old mice. After infection, they stop feeding, scatter throughout the cell and fall into a coma. Death occurs 24-36 hours after infection. In the brain, the virus reaches a titer of 106 -108 MLD 5o/ml of tissue and it is used to obtain the KS antigen, which is necessary for detecting antibodies in the sera of recovered animals using RSC. Field strains can be isolated from 1-4 day old mice after 2-4 blind passages.
Blob virus strains adapted to chick embryos or mice reproduce well in the brain of newborn golden hamsters and can be used in the same way as baby mice. Dogs, cats, rabbits, guinea pigs, and ferrets are not sensitive to the BTV virus.
The cytopathic effect of the BTV virus on sheep kidney cell cultures was first reported by McCercher, Haig and Alexander in 1965. Fernandez (1959) reported that lamb kidney cell cultures were sensitive enough to isolate the virus from the blood of diseased sheep. The sensitivity to this virus of such continuous cell lines as HeLa, human amnion, sheep kidney, etc. was established. But the most sensitive of them, according to Tini et al., were BHK-21 and L cells (Howell et al., 1967) .
Currently, primary cultures of lamb kidney and cattle embryo cells, as well as BHK-21 and B, are most widely used for the isolation and propagation of the BTV virus. The virus is synthesized in the cytoplasm of cells and slowly leaves them, starting from the 8th hour after infection, maximum accumulation is 30-36 hours after infection.
CPD in lamb kidney cells is manifested by the fact that the epithelial-like cells are rounded and wrinkled, and at this time the fibroblast-like cells are stretched and form lace-like strands, among which the rounded epithelial-like cells shine; then necrosis occurs with the formation of a mass of cellular detritus. In the cytoplasm of infected lamb kidney culture cells, specific inclusion bodies are formed; they are eosinophilic, of different sizes, with a light rim and are the sites of virion formation.
Sources of infection and routes of transmission. The BTV virus is capable of multiplying in mammals (ruminants) and insects. Under natural conditions, vertebrates become infected through the bites of blood-sucking insects.
Under experimental conditions, sheep can be infected by intranasal, intravenous, intraperitoneal, subcutaneous, intradermal, intramuscular and nitrapericardial administration of the BTV virus. An aerogenic route of infection is also possible. Jochim, Lyudke and Boal managed to experimentally infect sheep by giving virulent blood through the mouth 3 times a week for 26 weeks. The authors concluded that per os infection depends on the duration and frequency of contact of the body with the virus, but not on the amount of infecting material. After prolonged exposure to the virus per os, sheep acquire increased sensitivity to subsequent infection subcutaneously. At the same time, the animals became more seriously ill and some died. In this regard, the case in 1962 in South Dakota and Wyoming, when the most severe TB occurred in herds that used poor watering, can be explained. On one farm, BLO caused 100% disease and the death of about 25% of Sheep, and on the neighboring one, located a quarter of a mile away, there was no disease at all. It turned out that in the first case, the sheep were watered in a pond, the water of which was contaminated with the secretions of sick animals, and the second herd was watered with water stored in special tanks. It is believed that sheep could become hypersensitized to the BTV virus by long-term absorption of water contaminated with virus-containing urine.
Infection of animals through direct contact with patients has not been recorded either experimentally or under natural conditions.
Apart from the described case of virus isolation in urine and several other fragmentary information about similar virus isolation, there is no information about the isolation of viruses from the body of sick animals, either in experimental or in natural conditions.
The transmission of the virus by blood-sucking insects under natural conditions has been reported for a long time (Hatchen, 1902; Opreus, 1902; Dixon, 1909). But only in 1944 Du Toit showed that biting midges from the river. Culicoides transmit the virus from one animal to another through blood sucking. He also managed to infect sheep with a suspension of ground midges caught in natural conditions. In 1963, it was experimentally shown that Culicoides variipennis can transmit CLO from one animal to another among sheep and cattle, regardless of the type of animal. It was found that the virus actively multiplies in the body of biting midges and accumulates in the salivary glands to higher titers ( 107 -108) than in the body of sheep.
BLO is a seasonal disease, as it is associated with the summer periods of midges. Typically, BWB occurs in spring and early summer and spreads mainly in river valleys, lowlands, and swampy areas abounding in biting midges. Sheep grazing in such places, especially in the evening and at night, is associated with an increased risk of BTV infection.
It has been established that in an enzootic zone several antigenically different types of virus can circulate among insects, while only one type of virus is isolated from the body of naturally infected animals, which after a short circulation can be replaced by another (Du Sois and Haven, 1962). Howell (1963) admits the possibility of interference of field strains of the virus in the body of infected animals.
In sheep, the virus is found in the blood, serum, plasma and organs. The infectivity of sera is almost the same as that of whole blood, indicating that the virus is not adsorbed to red blood cells. The virus is also isolated from the blood of fetuses.
According to Du Toit (1928), the BTV virus remains in the body of recovered sheep for about 4 months, periodically appearing in the blood. A number of authors have detected the virus in the blood of sheep a maximum of 21-26 days after infection.
According to the famous American researcher KLO Ludke (1969), the virus was detected in the blood of sheep from 1 to 31 days after infection, but in most animals viremia occurred between 3 and 10 days after infection. Peak viremia usually occurred on days 6–8. In some animals, the virus was detected in the blood on days 21-31 after infection, when the presence of neutralizing antibodies was already established in the serum. Most researchers still believe that in sheep the period of viremia is relatively short and in most cases occurs on the 10-21st day after infection.
There is an opinion that in the natural focus of BTV, the epizootological role of sheep as a reservoir of the virus is less than the role of cattle, in which BTV usually occurs as a latent infection. But in cattle the period of viremia is much longer than in sheep. Under experimental conditions in cattle, viremia in high titers is observed from the 2nd day after infection, reaches a peak on the 7th day and gradually decreases by the 24th day. But with more sensitive methods (infection of sheep), it was possible to detect the virus in the blood of cattle even on the 50th day after infection (when neutralizing antibodies also circulate). Viremia has been described in cattle under natural conditions with a latent course of BLO up to 4-5 months (Du Toit, 1962; Aries, 1965). During this time, viremia may be periodic due to cases of re-infection with heterologous strains. According to Lüdke et al. 1970), naturally infected cattle with signs of disease similar to foot-and-mouth disease may have lifelong viremia. This fact allowed some authors to believe that cattle can serve as a reservoir in which the BTV virus persists in winter.
Under experimental conditions, it has been shown that the BTV virus can be serially passaged through cattle without increasing its virulence for cattle and sheep (Gray et al., 1967). It has also been established that strains of the BTV virus isolated from cattle have low pathogenicity for sheep (Lüdke, Bodn, 1970), and also that Culicoides variipennis more actively attacks cattle lambing than sheep. In South Africa, during the period of activity of these vectors, the BTV virus appears first in the blood of cattle, and then in sheep.
In connection with the above, it is increasingly suggested that cattle are the main host of the BTV virus (Du Toit, 1962). In any case, cattle are the most important factor in the epizootology of TB.
Epizootological data
Under natural conditions, sheep of all breeds are most susceptible to the pathogen, but Merino sheep are more sensitive. Cases of the disease have also been described in cattle, goats, deer, and antelope. Cattle become ill mostly asymptomatically. Infectious bluetongue occurs in the form of epizootics with a large coverage of the livestock (50-60% of the herd), characterized by seasonality (warm, wet season) and a more severe course of the disease in animals exposed to solar radiation.
Biological carriers of the virus are various species of midges of the genus Culicoides; sheep bloodsucker Melophagus ovinus (mechanical vector). During the inter-epizoonic period, the virus apparently persists in the body of many species of wild ruminants and cattle, among which long-term circulation of the virus has been established (over three years). Being the main reservoir of the pathogen, infected cattle ensure the stationarity of epizootic foci of the disease.
In insects, transovarial transmission of the pathogen and transmission during metamorphosis have not been established; they, apparently, do not take part in the preservation of the virus during the inter-epizootic period. In primary epizootic foci, mortality reaches 90%, in stationary ones - 30%.
Pathogenesis
Little studied. It is assumed that after the initial period of virus replication near the site of entry, generation occurs through the bloodstream. The virus is then localized in epithelial and muscle tissues, as evidenced by degenerative and inflammatory changes in them. The virus enters the blood within 1-2 days after infection of sheep, reaching its maximum titer on the 6-8th day. The virus appears in other organs and tissues after the onset of fever. Thus, the virus was detected in the spleen 48 hours after the onset of fever. As clinical manifestations of the disease develop, the virus becomes increasingly difficult to isolate from the blood (probably due to the appearance of antibodies). After the febrile reaction has subsided, the virus can only be isolated with great difficulty, sometimes only after blind passages on sheep. The virus is localized and affects the epithelium of the oral and nasal cavities, the intestinal mucosa, causes degenerative changes in the muscles, which are clinically manifested by emaciation, stiffness of movement, curvature of the neck, etc. V "rus passes through the placental barrier, as it is found in the blood of fetuses of sheep and cattle livestock Blositis disease is often accompanied by activation of secondary microflora, which leads to the development of bronchopneumonia and other complications. The blood sugar content of sick sheep increases, and in severe cases, the level of hemoglobin and total protein decreases. In all cases, leukopenia is noted.
In pregnant sheep and cows, BLO causes abortions and fetal deformities in the form of underdevelopment, encephalopathy, shortening of limbs and jaws, etc. (Griner et al., 1964). The 5th-6th week of pregnancy is especially dangerous for embryos (Bown et al., 1964). There are observations that the vaccine virus in ewes can disrupt the normal estrus cycle and cause temporary sterility.
Clinical symptoms
Clinical manifestations of BLO and morphological changes in natural and experimental conditions vary depending on: the pathogenicity of the strain, individual characteristics and breed of animals; influence of environmental conditions (meteorological).
In enzootic foci, the disease primarily affects animals imported from prosperous areas, as well as young animals of the current year of birth. An outbreak of BTV in Israel was described, observed only on one farm, where fine-wool sheep were imported from Germany (Dafnes, 1966).
The incubation period under natural conditions has not been precisely established, but it is believed to be 6-8 days. Under experimental conditions, with intravenous injection of the virus, a 2-8-day incubation period was registered, in exceptional cases - up to 15 days. After the incubation period, a rise in temperature is noted to 40.6 - 42.0 °; fever lasts from 6-8 to 12 days. It is noted that the temperature does not correlate with the severity of clinical symptoms. Thus, mild intermittent fever can be accompanied by severe clinical symptoms and death of animals. At the same time, a sudden rise in temperature to 42° can result in only mild symptoms and rapid recovery. As the temperature rises, an increase in breathing is observed. 24-36 hours after the first rise in temperature, hyperemia of the skin of the muzzle, lips, ears, as well as the mucous membranes of the oral and nasal cavities develops, accompanied by the flow of foamy saliva and peculiar continuous movements of the tongue. Muco-catarrhal discharges appear from the nasal cavity. , sometimes mixed with blood. The lips and tongue become noticeably swollen, the muzzle becomes larger and darker in color, and pinpoint hemorrhages appear on the mucous membranes of the mouth, nose, and eyes. In a small percentage of cases, the tongue turns red-blue (hence the name of the disease). Hair falls out on the face, erosions form on the mucous membranes of the mouth and nose, which bleed easily. In more severe cases, the mucous membranes of the cheeks, gums and tongue ulcerate and bleed, saliva mixes with blood and necrotic tissues, and takes on an unpleasant odor. Nasal discharge becomes purulent and crusts around the nose, causing anxiety to animals; thirst develops. Due to pain in the mouth, food intake is stopped and the animal lies on its side. In cases ending in death, enteritis develops, accompanied by diarrhea. Sometimes at the height of the fever, but more often after the temperature subsides, redness of the crown of the hooves with increased temperature and pain when pressed can be seen on the hind limbs. The redness then progresses to a bluish discoloration with dark red patches, followed by irregular hoof growth with waviness. By the number of these wavy lines, one can judge the number of types of virus that the animal has had. Soreness leads to lameness, reluctance to move, and a stiff gait. The back arches, and sheep often move towards the feed on their knees, driven by hunger. Inability to feed and muscle damage lead to progressive wasting, accompanied by intestinal dysfunction. Animals can remain in this state for up to 10 days and then until death - in prostration and exhaustion. 3-4 weeks after the fever stops, the hair begins to fall out, hanging in clumps. The duration of the illness varies. Lesions in the oral cavity can heal slowly (depending on the secondary microflora). With a mild course of the disease, short-term fever and transient hyperemia of the oral mucosa are noted. In acute cases, swelling of the pharynx and paresis of the esophagus can cause severe aspiration pneumonia; in the blood - leukopenia, poikilocytosis, and later anemia. In especially severe cases, hemoglobin and total nitrogen decrease. After the 8th day from the moment of infection, a pronounced increase in γ-globulins and a less pronounced increase in globulins are noted, the level of α1 and α2 tlobulins and albumin is reduced.
In the subacute course, the described signs are less pronounced, changes in the mucous membranes of the head, inflammation of the skin, hooves, exhaustion, hair loss are noted, death can occur only after a year.
In case of abortive course (sometimes), which is possible after vaccination, mild fever occurs, mild hyperemia of the mucous membranes without ulceration, appetite is preserved.
In most cases, BTV in cattle occurs as a latent infection, especially in enzootic zones. At the initial onset of the disease, symptoms resembling foot and mouth disease and TB in sheep have been described. Recently, there have been reports of abortions and the birth of deformed, dwarfed and underdeveloped calves.
Pathological changes
At autopsy, the following changes are found: the subcutaneous tissue and muscle connective tissue are swollen, saturated with a yellowish liquid. The tissues of the lips, tongue, ears, pharynx and larynx, intermaxillary region, and chest are also swollen. The edematous fluid sometimes acquires a reddish color from the admixture of blood or a gelatinous consistency. There may be an accumulation of edematous fluid in the chest and abdominal cavities and in the pericardium.
If the animal died in the acute period of the disease, then the most pronounced changes are observed in the digestive system: the oral mucosa is hyperemic, swollen, cyanotic, and covered with hemorrhages of varying sizes and shapes. On the lips, tongue, and inner surface of the cheeks there are ulcerations, sometimes extensive, covered with dirty grayish necrotic masses through which blood seeps. In the rumen and mesh, in the abomasum, hyperemia and hemorrhages are observed, most pronounced on the papillae and leaflets. The gullet of the esophagus can be hyperemic, covered with ulcerations and even foci of necrosis. The mucous membrane of the abomasum is diffusely hyperemic, sometimes cyanotic and covered with hemorrhages of various shapes and sizes. In the swollen intestine, inflammatory changes vary from focal hyperemia to a catarrhal process throughout (up to the thick section). The nasal cavity is filled with dirty yellow catarrhal contents flowing from the nose. The nasal septum is swollen, blood-filled and covered with ulcerations. The trachea contains foamy fluid that appears when the lungs are swollen or congested.
Changes in the vascular system are characterized by hyperemia of all tissues, edema and hemorrhages. There is a small amount of fluid in the cardiac sac, as well as hemorrhages under the epicardium and endocardium. In the medial layer at the base of the pulmonary artery in acute cases, as a rule, there is hemorrhage. Sometimes foci of necrosis are found in the papillary muscle of the left ventricle, which can spread throughout the entire heart muscle.
The spleen and lymph nodes are usually only slightly enlarged. The most often affected are the retropharyngeal, cervical, mediastinal, maxillary, bronchial, mesenteric, prescapular, sublingual lymph nodes, which in this case are enlarged, reddened and swollen. In the liver - venous stagnation and degenerative changes. In the kidneys - hyperemia, edema.
The main changes occur most consistently in the skin and muscles. Sometimes lesions on the skin of the muzzle and crown of the hooves are limited only to redness. More often, the redness on the corolla is replaced by the appearance of point foci, which merge and form vertical reddish stripes in the substance of the horn. These changes are most often observed in the hind limbs.
Changes in the muscles are expressed by swelling of the intermuscular connective tissue and fascia with a reddish gelatinous fluid. The muscles of the thighs, shoulder blades, back, and sternum are often affected (Moulten, 1961). They reveal small (1-2 mm) hemorrhages, as well as foci of necrosis. Degenerative changes in muscles are sometimes so profound that the muscles acquire a grayish tint and look like boiled.
Histological changes in K. LO are limited mainly to three systems:
1) mucous membranes of the gastrointestinal tract;
2) skeletal muscles;
3) vascular system.
It should be noted that with a protracted course of the disease, all acute phenomena, such as hemorrhages and ulcerations in the oral cavity, are no longer detected at autopsy. All sorts of secondary complicating processes, such as bronchopneumonia (even purulent and gangrenous), can come to the fore here. In pregnant sheep, changes in the placenta indicate a direct effect of the virus on the vascular system of the maternal body and fetus, as well as transplacental penetration of the virus (in 3% of cases).
In enzootic foci of infection, where many animals become ill due to unclear symptoms, most often the listed changes may not be found at autopsy. Changes are limited to exhaustion, anemia, slight accumulation of fluid in the cavities and mild catarrhal inflammation of the mucous membranes of the gastrointestinal tract.
It must be borne in mind that the described changes can vary greatly in intensity, they may or may not be present - it all depends on the conditions under which the infectious process occurs.
Diagnostics
The diagnosis of BLO is made on the basis of epidemiological, clinical, pathological and morphological data and laboratory test results.
From epidemiological data, the appearance of the disease in a hot rainy period, the simultaneous increase in the number of blood-sucking insects, the nature of the terrain (lowlands, wetlands, river valleys, etc.), and the presence of imported animals (from safe zones) are important.
Clinical symptoms include fever, depression, cyanosis of the tongue, lips, gums, swelling of the muzzle, curvature of the neck, and lameness. The degree of their severity can vary within very wide limits.
Of the pathological changes worthy of attention. exhaustion, swelling of the subcutaneous and intermuscular connective tissue, degenerative changes in skeletal muscles, necrosis of the mucous membranes of the mouth, tongue, lips, etc.
The presence of these signs and the detection of antibodies to the BTV virus in the blood of animals using RSC allows a preliminary diagnosis of bluetongue in sheep to be made.
The final diagnosis is based on the results of experimental infection of sheep, isolation and identification of the virus. The virus can be isolated:
1) from whole blood obtained during fever;
2) from the spleen;
3) from lymph nodes (especially mesenteric ones taken in the acute stage of the disease). The material for virus isolation is taken into Edington's preservative liquid. To isolate the virus, either 6-8-day-old chicken embryos or cell cultures (PY, BHK-21, L, BEP, etc.) > or suckling mice (intracerebrally) or sheep (the most sensitive object) are infected with pathological material. As a rule, the virus is isolated after several blind passages. Even on sheep, sometimes it is necessary to carry out 2-3 passages.
To differentiate the isolated virus from other viruses, RSC is used, and for typing, a neutralization reaction is used. RSC for TB is group-specific and can be used to detect antibodies to any strain of the TB virus. RSK is used for serological reconnaissance of the area for the circulation of the BTV virus in it. The neutralization reaction is used to study the immune status of the animal and to type the isolated virus. The best results are obtained with long-term (24 hours) contact of the virus with serum at a temperature of +37°.
A quick result is obtained by using the method of fluorescent antibodies with a culture of infected cells. Specific luminescence is detected already in the 1st passage of the virus in cell culture, when there is no CPE yet. In addition, in an infected cell culture, specific inclusion bodies can be detected already in the 1st passage.
In the USA, RDP is quite widely used to detect precipitating antibodies in the blood of recovered animals. The antigen is a purified and concentrated culture virus. The advantages of RDP are simplicity and speed. The disadvantage is insufficient specificity (therefore the method is suitable only for indicative diagnosis).
Differential diagnosis
Infectious bluetongue must be distinguished from foot-and-mouth disease (high contagiousness, characteristic foot-and-mouth lesions of the oral cavity, udder, limbs, results of virological studies), contagious ecthyma of sheep (contagiousness, pustular lesions of the mucous membranes and skin, microscopy of smears from pathological material, bioassay on lambs and rabbits), malignant bluetongue (sheep rarely get sick, the disease is mostly sporadic, characterized by damage to the eyes and upper respiratory tract), necrobacteriosis (in addition to sheep, horses, pigs and other animals get sick, chronic course, excretion of the pathogen), Ibaraki disease (sick cattle, results of virological and serological studies), epizootic hemorrhagic disease of deer (virological and serological studies).
BLO must be differentiated from the following diseases:
Hydropericarditis.(An extremely dangerous non-contagious disease of sheep, caused by Ricketsia ruminantum and transmitted by Amblioma ticks. Characterized by fever and nervous symptoms. Distributed in the same areas of Africa as BLO. With BLO there are no nervous symptoms, the fever is longer lasting, the course is slower, and cannot be treated with antibiotics .
Rift Valley Fever. Mortality in sheep is up to 100%, in calves - 70-100%, abortions. At autopsy, necrosis and degeneration in the liver, acidophilic inclusions in liver cells.
Differentiation from KLO by RA, MFA, RSK, RZGA.
Sheep pox. Lesions of the skin and mucous membranes of the mouth,
respiratory tract, gastrointestinal tract. With K. LO - lesions only in the oral and nasal cavities, lack of contagiousness.
Contagious ecthyma of sheep. Formation of papules and vesicles on the lips and nostrils, sometimes around the eyes. They are replaced by pustules and a thick crust, and are not accompanied by swelling and hyperemia of the mucous membranes, which is characteristic of clot. Difference from BLO and in epizootology.
Foot and mouth disease. Lesions develop quickly, affect a large percentage of animals, the disease is highly contagious, and aphthae is present. There is none of this with KLO.
"Weeping disease." This disease occurs in calves aged 1 week to 6 months, is transmitted by ticks, and is characterized by stomatitis, hyperemia of the mucous membranes and skin with the development of wet eczema. Diphtheretic inflammation often develops in the mouth and pharynx. The disease is not transmitted through blood to sheep and is characterized by severe disease and mortality.
Vesicular stomatitis. Can be differentiated from BLO based on epizootology. Horses also get sick.
Three-day disease of cattle. ( Stiffsickness - stiffness of movements). It manifests itself as lameness, stiffness of movement, paresis (passes quickly), high fever (passes quickly). There is no hyperemia and it is not transmitted to sheep (like BLO).
Immunity and prevention
Sheep that have recovered from the disease acquire lifelong immunity to the type of virus that caused the disease. Recurrent disease is possible during the same season or the following year, but only if infected with a different type of virus (Howell, 1966).
In naturally ill animals, virus-neutralizing antibodies appear 6-9 days after infection and reach their maximum titer by the 30th day. Complement-fixing antibodies appear only 10-14 days after infection and reach a maximum titer also by the 30th day, remaining at a high level for 3-4 months, after which their titer gradually decreases to barely perceptible by the end of the year. In sick animals, precipitating antibodies are formed (Klontz, Svekhach, Gorham, 1962).
All types of the virus have a common complement-fixing antigen, which makes it possible to detect any type of virus using RSC. Typical differences are found in the neutralization reaction.
Attempts to reduce the number of vectors through the use of insecticides are usually unsuccessful. The appearance of BW in an epizootic zone can be predicted and preventive measures can be taken in advance. Thus, before the start of the insect summer period, it is useful to transfer all sensitive animals (young stock of the current year of birth, newly imported purebred sheep) to a higher pasture. It is advisable to have premises for sheltering animals at night. Animal parking areas can be treated with insecticides (some animals can also be treated individually).
In 1902-1905 Spreul proposed simultaneous vaccinations, in which sheep were simultaneously injected with virus-containing sheep blood and convalescent serum. The method turned out to be dangerous and unreliable.
In 1907, Theiler's vaccine came into practice. Theiler believed that the virulent properties of the virus are weakened by serial passages in sheep. As a vaccine, he proposed a virus that had undergone 18 passages on sheep. Theiler's vaccine, which is a mixture of virus-containing blood and preservative liquid, was administered subcutaneously in a dose of 1 ml. Each batch of vaccine was tested on 2 or more sheep and released only if... it caused a feverish reaction. Mortality among vaccinated sheep decreased to 0.5%, versus 11% among unvaccinated sheep.
In 1927, a new strain of the Blob virus was used to prepare a vaccine, as Du Toit feared that after 20 years of use, Theiler's strain had become too weakened to provide good immunity. Despite the replacement of the strain, complaints continued to be received about severe post-vaccination reactions (especially in the hot summer months), as well as the lack of strong and long-lasting immunity in vaccinated sheep.
In 1937, attempts were again made to find a satisfactory vaccine. The Theiler strain was taken again and stored at room temperature for 25 years. In 1938-1940 Neutua showed that Theiler was mistaken, that he had come across a natural, weakly virulent strain, and that the BTV virus did not change its properties during passages on sheep. This conclusion of Neutois was supported by all other researchers, with the exception of Du Toit, who reported the successful attenuation of a strain of BTV virus by passages in sheep.
Complaints about Theiler's vaccine can be explained by the fact that it contained only one type of virus, whereas many antigenically different types are circulating in Africa. For case immunity, a polyvalent vaccine is required.
Alexander and his colleagues found that sequential passage of the BTV virus on chicken embryos leads to a weakening of its virulence in sheep. Optimal results were obtained when 8-9-day-old embryos were infected into the yolk sac and incubated for 3-4 days at 33.5°. The virus titer reached 105 -106 ELD50 /g tissue. In this way, it was possible to modify virulent strains so that they practically did not cause a clinical reaction in sheep. Subsequent 11-fold passages of the resulting attenuated strains in sheep did not change the virulence. This is how vaccine strains of different types of virus were obtained, and in 1951 they began to use a 4-valent live virus vaccine. Every strain. were cultivated separately in chicken embryos (passage level from 30 to 101), and then the resulting material was mixed so that the finished vaccine contained 250 ELD50 of each strain in 1 ml. The vaccine is administered subcutaneously in 1-2 ml doses. Annual vaccination is recommended, since post-vaccination immunity is established through the reptile, but how long it lasts is not known. To avoid post-vaccination complications, mass vaccination is recommended after sheep shearing.
Vaccination of pregnant ewes is avoided, as attenuated strains cause abortions and the birth of malformed lambs. Vaccination of breeding rams can cause their temporary sterility, so rams are vaccinated after the breeding season. Lambs born from immune ewes remain immune until 3-6 months of age and during this period do not respond to vaccine immunization.
Since 1961, a vaccine made from viruses grown in calf kidney cell cultures began to be introduced into practice. According to Lyudke and Dnokhim, a cultured vaccine is less likely than an embryonic vaccine to cause post-vaccination complications and almost does not cause a clinical reaction. However, the widespread use of live vaccines faces a number of objections. Thus, according to researchers from South Africa and the USA, live vaccines often cause diseases in sheep that are almost indistinguishable from those that occur naturally.
In 1968, Foster, Jones and Lüdke reported that vaccinated sheep were viremic, and biting midges feeding on them could transmit the virus to other sheep that became seriously ill (one bite of a biting midge was enough to cause disease in the sheep). Therefore, TB specialists believe that live vaccine should not be used in prosperous areas, since in this way new foci of the disease can be created.
Based on the above, we can conclude that, apparently, vaccination does not lead to the eradication of the disease, it only prevents further spread and reduces economic losses. From this follow:
1. The need to prepare a vaccine from local strains;
3. More strict control of vaccine strains for reversion.
Treatment
Currently, there are no drugs that specifically act on the BTV virus in vivo. The success of the use of antibiotics and sulfonamides is explained by their effect on secondary infections, especially with the development of bronchopneumonia.
Careful care of sick animals is the most important measure. Sick animals must be placed in areas protected from direct sunlight. A small amount of tender green food at a time when lesions on the oral mucosa cause pain when eating food helps to improve the condition of the animals. Surface lesions are moistened with disinfectants and alcohol lotions are made. During the recovery period, it is most important to maintain and, if necessary, stimulate rumen activity. Careful and good feeding and care will help shorten the recovery period and restore normal conditions.
Control measures
In areas that are permanently unaffected by infectious bluetongue in sheep, it is necessary to vaccinate susceptible livestock at least a month before the onset of the disease season.
When a disease appears, vaccination should also be carried out using vaccines against the type of pathogen that caused the disease in a given outbreak. At the same time, measures are taken to protect animals from insect attacks. Restrictive measures are also being introduced.
Currently, there are no internationally accepted instructions for combating BWB. The International Bureau of Epizootics has developed only the following basic principles for preventing the introduction of BW into free countries.
1. Prohibition of the import into TB-free zones of sheep, goats, cattle and wild ruminants, as well as their sperm, blood and serum from countries (or outbreaks) unaffected by TB.
2. Destruction of BW carriers on all vehicles (ships, planes, cars, trains, etc.) arriving from countries (foci) affected by BW.
3. When importing susceptible animals from countries considered TB free, it is necessary to require the presentation of an international veterinary sanitary certificate certifying that the imported animals are from a TB free zone (country), that they have undergone a 40-day quarantine and have been subjected to diagnostic tests.
4. Animals imported from other countries must be quarantined for 30 days. During the quarantine period the following is carried out:
a) daily clinical examination and thermometry;
b) examination of blood serum at the RSC for the presence of antibodies to the BLO virus;
c) pathological material (blood, affected muscles) is taken from animals suspected of having the disease for virological and pathomorphological studies.
If sick animals or virus carriers are detected, the entire group of imported animals is killed using meat for sausages and canned goods.
5. When a BWB is established on a farm, a populated area with designated grazing areas is declared unfavorable, quarantine is imposed on it and the following measures are carried out:
a) The export of domestic and wild ruminants to other farms is prohibited;
b) The export of semen, blood and serum from domestic and wild ruminants is prohibited;
i) All transport leaving the unfavorable area must be treated with insecticides;
d) Constant veterinary supervision is established for unfavorable flocks of sheep. Sick sheep are isolated, treated symptomatically and treated with insecticides.
e) Premises, pens where unhealthy flocks were kept, as well as slaughter areas must be disinfected: with a 2-3% solution of sodium hydroxide, a solution of sodium hypochlorite, bleach or a 2% solution of formaldehyde.
f) During the period of insect activity, it is necessary to keep sheep on elevated areas of pastures, and at night drive them indoors and free them from “insects”.
6. The slaughter and use for meat of sheep infected with BWB is permitted within disadvantaged areas with the permission of veterinary authorities.
If there are degenerative changes in the muscles, gelatinous infiltrated connective tissue in the intermuscular spaces, redness of internal and subrenal fat, hemorrhages in the subcutaneous tissue, the entire carcass is sent for technical disposal.
7. Skins obtained from the slaughter of sick animals or removed from corpses are rendered harmless by rubbing with a curing mixture containing 83% table salt, 7.5% ammonium chloride and 2% soda ash, followed by storage and storage for at least 10 days.
8. In disadvantaged areas (outbreaks), all sheep are subjected to preventive vaccination:
adult sheep - 3-4 weeks before mating;
stud rams - after mating;
lambs - upon reaching 5 - 6 months of age.
Vaccinated animals are kept in cool places protected from the sun, insects and ticks for 10 to 14 days after vaccination.
9. Sale, exchange, transfer to other farms of domestic and wild ruminants from disadvantaged areas is prohibited.
Conclusion
So, over the years, BWB was registered in 40 countries around the world. In recent years, the disease has been constantly recorded in 18-20 countries in Africa, the Near (Syria, Israel, Turkey), Middle (Pakistan, India) and Far (Japan, inaccurate) East.
Economic losses from BWB are enormous and arise due to the death of animals, loss of their productivity (wool, meat) due to long recovery, costs of vaccination and diagnostics.
Sheep mortality is 5-10% (USA, Japan), but particularly virulent strains cause up to 85% mortality (Cyprus, Portugal, Israel).
Currently, there are no drugs that specifically act on the BTV virus in vivo. The success of the use of antibiotics and sulfonamides is explained by their effect on secondary infection.
Infectious catarrhal fever is not registered with us. The main attention is paid to preventing its introduction into our country with imported domestic (sheep, goats, cattle) and wild ruminants. Preventive quarantine is mandatory, with virological and serological studies carried out if necessary.
List of used literature
1. Laktionov A.M. Sheep bluetongue virus. In the book: Guide to veterinary virology. - M., 1966, pp. 482 - 486.
2. Syurin V.N., Fomina N.V. Infectious bluetongue virus of sheep In the book: Private virology (reference book). - M., 1970, pp. 174-181.
3. Syurin V.N. Bluetongue of sheep In the book: Laboratory diagnosis of viral diseases of animals. - M., 1972, pp. 266 - 277.
4. Syurin V.N., Samuylenko A.Ya., Solovyov B.V., Fomina N.V. “Viral diseases of animals”, M.: VNITIBP, 1998, pp. 85-96.
5. Syurin V.N. Private veterinary virology. M., Kolos, 1979, pp. 11-178.
6. Arkhipov N.I. and others Pat. anat. vir. bol. zhiv., M., Kolos 1984, pp. 24-57.
7. Varovich M.F. Questions of Virology, 1991, pp. 1-21.
8. Zharov A.V., Shishkov V.P., Zhakov M.S. et al., Pathological anatomy of farm animals. - 4th ed., revised. and additional - M.: KolosS, 2003. -568 p.
9. Razumov I.A. and others. Molecular genetics, microbiology, virology. M., Kolos, 1991, pp. 6-21.
10. Avylov Ch.K., Altukhov N.M., Boyko V.D. and others, Directory of a veterinarian / Comp. A.A. Kunakov. - M.: KolosS, 2006-736s.
