Naturally focal infections classification. The main natural focal diseases of Russia

Among natural focal infections, two large groups are distinguished: with a transmissible and non-transmissible mechanism of pathogen transmission.

A distinctive feature of a large group of vector-borne infections is the transmission of the pathogen through blood-sucking arthropods: lice, fleas, mosquitoes, mosquitoes, ticks, etc. The causative agents of infections belonging to this group can be various microorganisms: viruses, bacteria and protozoa. Some vector-borne diseases are characterized by natural focality, that is, the ability to spread only in certain geographical areas, which is associated with the biological characteristics of the carriers, whose life activity can only occur in certain natural conditions.

Despite the fact that the main specific component of a natural focus is the pathogen population, in the case of vector-borne infections it is also characterized by a specific vector. This is how a group of ixodid tick-borne infections has emerged, the causative agents of which are transmitted by ticks of the genus Ixodes: tick-borne encephalitis (tick-borne encephalitis virus), Powassan encephalitis (Powassan virus), ixodid tick-borne borreliosis (Borrelia burgdorferi sensu lato), human granulocytic anaplasmosis (Anaplasma phagocytophilum), human ehrlichiosis (Ehrlihia chaffeensis, Ehrlihia muris), Q fever (Coxiella burnetii), bartonellosis (Bartonella henselae), some rickettsioses of the tick-borne spotted fever group (caused by R.sibirica, R.helvetica), babesiosis (Babesia divergens, Babesia microti, etc.) . In fact, the foci of these infections coincide with the geography of the distribution of ticks: forest I.ricinus and taiga I.persulcatus. I.persulcatus ticks have the largest distribution area: from Western Europe to Japan.

There are pathogens of tick-borne infections, mainly associated with other groups of ixodids - ticks of the genus Dermacentor: tularemia (Francisella tularensis), rickestia of the tick-borne spotted fever group, Omsk hemorrhagic fever virus. Since pasture ticks of the genus Dermacentor are more associated with plain-steppe and mountain-forest biotopes, rickettsiosis is mainly recorded in steppe landscapes in the south of Russia and in the Asian part of the country. The combination of pathogens by vector groups is given to understand the need for differential diagnosis of various infectious diseases that can occur when the same type of ixodid tick is sucked on. Moreover, ticks can transmit several pathogens at the same time, as a result of which a mixed infection will develop and the clinical picture of the disease will change. Among tick-borne infections over the past ten years, the highest incidence rate has been recorded for ixodid tick-borne borreliosis - on average 5-6 per 100 thousand population, for tick-borne encephalitis this figure is about 3.0 and for rickettsial infections - about 1.4.

Some of the listed pathogens carry out not only a transmissible route of transmission of infection to humans, but also contact (when rickettsia enters with tick feces on the affected areas of the skin and mucous membranes, crushing insects during tularemia), alimentary (infection with the tick-borne encephalitis virus and the causative agent of Q fever - when consumed raw milk, when consuming food and water contaminated with bacteria Francisella tularensis - for tularemia), aerogenic (rickettsiosis, Q fever, tularemia).

One of the significant and dangerous infections transmitted by Hyalomma marginatum ticks and endemic to the south of Russia is Crimean hemorrhagic fever. After a long period of epidemic prosperity (1973–1998), the 21st century saw a significant activation of old foci in the Stavropol Territory, Astrakhan and Rostov regions and the emergence of new foci in the Volgograd region, Kalmykia and Dagestan. This disease is characterized not only by a transmissible route of transmission of the virus, but due to the high level of viremia in the first days of the disease, a contact route of transmission is also realized, which must be taken into account by medical personnel providing care to the patient. In addition, possible cases of the disease should be identified among persons who were in contact with the patient before hospitalization.

Mosquitoes are a vector for a large number of pathogens of human infectious diseases. The most widespread and medically important are the viruses of Dengue, O, Nyong-Nyong, Japanese encephalitis, yellow fever, Venezuelan, eastern, western equine encephalitis, St. Louis encephalitis, West Nile, causing millions of epidemics, affecting tens and hundreds of thousands of patients. With the exception of the last disease, all of the listed viral infections do not have natural foci in Russia and can pose a significant threat only when traveling to endemic regions. West Nile virus, which caused an outbreak of diseases primarily affecting the central nervous system in the Volgograd, Astrakhan regions and Krasnodar Territory in 1999, continues to cause sporadic cases of the disease or outbreaks with the number of patients reaching several hundred people. In recent years, the area of ​​circulation of the virus has also spread to the Rostov and Voronezh regions; cases of West Nile fever have been registered in the Tambov region and Kazan. Another serious threat to public health is associated with the annual cases of importation of malaria into the Russian Federation from near (Azerbaijan, Tajikistan) and far (Africa, Southeast Asia, Central and South America) countries.

Thus, collecting an epidemiological history in the case of vector-borne infections, many of which are naturally occurring, is the first step towards deciphering the etiological agent of the disease.

On the territory of Russia, one of the most common non-transmissible natural focal diseases is hemorrhagic fever with renal syndrome, caused by hantaviruses of the Old World. The causative agents of HFRS are the Puumala, Dobrava, Hantaan, Seoul and Amur viruses. The last three circulate in the Far East, and until the end of the 20th century, it was believed that in the European part of Russia the disease was associated only with the Puumala virus. In 1997, for the first time in the Ryazan and Tula regions, in the first decade of the 21st century, large outbreaks of HFRS were registered in the central black earth region, etiologically caused in the overwhelming majority by the Dobrava virus.

Every year 5-7 thousand cases of HFRS are registered in Russia. The highest incidence is consistently observed in the Volga Federal District (Udmurtia and Bashkortostan), reaching 28 per 100 thousand population. The average mortality rate for HFRS is 0.5%, but in the Far East and, possibly, in the Krasnodar Territory, it is higher.

Another significant non-transmissible zoonosis in human infectious pathology is leptospirosis, which, according to WHO definition, is a zoonotic disease with a worldwide distribution. Every year this infection affects several hundred people in the Russian Federation, and the mortality rate can reach 20%.

Since most of the above infectious diseases do not have pathognomonic signs and require differential diagnosis with a number of clinically similar forms, the primary diagnosis must be confirmed using laboratory diagnostic methods.

Methods for laboratory diagnosis of natural focal infections include direct (detection of DNA/RNA of the pathogen, its antigens, visual detection of the microorganism by microscopy) and indirect (detection of specific antibodies IgM, IgG, IgA in blood serum, CSF, in the case of IgA - in tissue secretions) .

NATURAL FOCALITY OF DISEASES- a feature of some infectious human diseases, which consists in the fact that they have evolutionary foci in nature, the existence of which is ensured by the sequential transition of the causative agent of such a disease from one animal to another; In transmissible natural focal diseases, pathogens are transmitted by blood-sucking arthropods (ticks, insects).

Naturally focal are many viral, bacterial, protozoal diseases, helminthiases and some mycoses related to zoonoses (see). The most common and studied are tick-borne and Japanese encephalitis (see Tick-borne encephalitis, Mosquito encephalitis), hemorrhagic fevers (see), lymphocytic choriomeningitis (see), psittacosis (see), rabies (see), yellow fever (see) , some rickettsioses (see), tularemia (see), plague (see), brucellosis (see), erysipeloid (see), listeriosis (see), leptospirosis (see), tick-borne spirochetosis (see) , leishmaniasis (see), toxoplasmosis (see), opisthorchiasis (see), diphyllobothriasis (see), schistosomiasis (see), etc. Natural focal diseases are divided into vector-borne (in the presence of a carrier of the pathogen), subdivided into obligately transmissible and facultatively transmissible, and non-transmissible (transmitted without the participation of a carrier). Carriers (see), as a rule, are arthropods, carriers of the pathogen are vertebrates. Natural focal diseases are characterized by pronounced seasonality: diseases are associated with a person’s stay in certain places of a particular geographical landscape during the corresponding seasons of the year.

The presence of the pathogen in the body of vertebrate animals in some cases leads to disease, in others the animals remain asymptomatic carriers. The causative agent of the disease in the body of a specific vector goes through a certain part of its life cycle: it multiplies, reaches an infecting (invading) state and takes the position of exiting the vector. This process takes place in the body of an invertebrate animal (vector), which does not have a constant body temperature, and depends on temperature and its fluctuations in the environment. The microorganism and its carrier can be in a symbiotic relationship (see Symbiosis). In such cases, the pathogen finds a favorable habitat in the carrier’s body and at the same time does not have a noticeable adverse effect on its development, life and reproduction. Moreover, the pathogen adapts to the reproduction process of its carrier and, circulating in its body, sometimes penetrates the egg cells. From the infected eggs laid by the female carrier, daughters infected with the pathogen emerge, which, at the first sucking of the blood of susceptible animals, transmit the pathogen to them. The same may happen with the subsequent population. This is how transovarial transmission (see) of the pathogen occurs from an infected carrier to its descending generations. For the causative agent of tick-borne encephalitis, this was traced over two generations of the carrier, which may not be the limit. In other species ratios of the carrier and the microorganism, the latter has a certain patol. effect on the carrier’s body, which can shorten its life.

Interspecific relationships between the components of biocenoses of natural foci of diseases developed in the process of the evolution of microorganisms, animals - donors and recipients, as well as carriers in certain conditions of the emerging environment, regardless of the existence of humans, and for some diseases, possibly even before the appearance of the species Homo primigenius and Homo sapiens on Earth.

Thus, the natural focus of a human infectious disease is a section of the territory of a certain geographical landscape, in which certain interspecific relationships have evolved evolutionarily between the causative agent of the disease, animals - donors and recipients of the pathogen, and in case of vector-borne diseases - and its carriers in the presence of environmental factors , conducive to the circulation of the pathogen.

Natural foci of diseases are territorially associated with certain areas of the geographic landscape, that is, with its biotopes (see Biotope). In turn, each biotope is characterized by a certain biocenosis (see). The combination of a biotope and a biocenosis is a biogeocenosis (see). The nature of the biotopes is very diverse. In some cases it is clearly limited, for example. a rodent burrow with its various inhabitants in a hot desert zone. Such a biotope can be a natural focus of not one, but two or three different diseases: for example. The burrow of gerbils Rhombomys opimus is a natural site of tick-borne spirochetosis, zoonotic cutaneous leishmaniasis and some bacterial diseases. In other cases, the boundaries of the territory of natural foci of the disease are diffuse and therefore less defined in outline. Thus, the litter of broad-leaved taiga is a very favorable place for the tick Ixodes persulcatus, a specific carrier of the causative agent of tick-borne encephalitis, to stay outside the host. However, even over its vast area, these ticks are scattered unevenly, some places are free from them, while in others they accumulate in significant quantities, which happens on the paths of animals moving towards a watering hole.

Infected vectors in natural foci of the disease behave differently towards recipients, including humans; These differences are related to the method of movement and the search for “prey” for feeding. Flying carriers (mosquitoes, mosquitoes, etc.) can cover considerable distances, looking for suitable food items. For example, in the Karakum desert, phlebotomuses that hatch in the burrows of gerbils and other rodents fly out at night and, in search of food, can move away from their burrow to a distance of up to 1.5 km and attack people in the process. Crawling arthropods, e.g. ticks are not prone to distant migrations; they crawl not far from the place where they hatch from the eggs or from the place of molting. Climbing onto grass, low bushes or dead wood exposed after the snow melts, they take a lurking pose and remain in place until they cling to a passing animal or person, after which they begin the act of blood sucking.

Natural foci of diseases exist due to the continuously occurring transmission of the pathogen from the body of one animal to the body of another. Such foci can remain unknown to a person for centuries until he enters their territory, but even then, human disease occurs only under a combination of the following conditions: the natural focus of a vector-borne disease must be in a valence state, i.e., there must be hungry, infected people on the territory of the outbreak the causative agent of the disease is carriers, ready to attack emerging people as a tempting source of abundant food; people entering the territory of a natural outbreak must be non-immune to this disease; carriers must introduce into the human body a dose of the causative agent of the disease sufficient for its development; the pathogen itself must be in a virulent state.

Apparently, cases of introducing small doses of the pathogen into the body, which are insufficient for the development of the disease in an infected person, are practically more frequent. However, this process does not go unnoticed for the recipient; His body produces antibodies to the introduced pathogen, and the person becomes immune to the action of new doses of the pathogen, sufficient under normal conditions for the full development of the disease. In this case, the carrier of the pathogen can have a positive effect on the human body, leading it to a state of immunity to the pathogen of the corresponding type. The presence of antibodies to pathogens of some natural focal diseases, for example. tick-borne and mosquito encephalitis has also been found in animals that do not suffer from these diseases, which is associated with their prolonged stay in the territory of the natural focus. Detection of antibodies in people and animals in certain areas is an important diagnostic method for detecting hidden natural foci of corresponding diseases.

To characterize natural foci of diseases, it is important to know the conditions for the persistence of their existence and to have a clear understanding of the possibility of their movement. Both of these issues are closely related to each other. It is known, for example, that natural foci of tick-borne encephalitis and some tick-borne rickettsioses can only exist in certain natural conditions, since ixodid ticks, carriers of the pathogens of these diseases, cannot, as a rule, live and reproduce close to humans, much less stay in his home. It is, of course, possible that single infected ticks may be brought into a person's home, which can lead to sporadic diseases, but this is an exception. At the same time, carriers and carriers of pathogens of natural focal diseases can, under suitable conditions, move to new habitats, which significantly modifies the epidemiology of the corresponding disease. As a result of such movements, carriers of pathogens of natural focal diseases can move into housing or end up in the immediate environment of a person. In this case, intra-household diseases of people arise (for example, tick-borne relapsing fever, cutaneous leishmaniasis, plague and certain other diseases). Thus, Ornitllodoros papillipes ticks - carriers of spirochetes - the causative agents of tick-borne relapsing fever - can settle in the burrows of Turkestan rats located in housing, forming a kind of burrow biocenosis with house rodents. Such foci of infectious diseases, associated in their origin and maintenance of existence with some form of human activity, are called anthropourgic.

No matter how the natural foci of diseases undergo modifications, their primary connection with geographic landscapes does not lose its fundamental significance even when the causative agent of the disease is transmitted by many types of vectors and, in addition, by various non-transmissible methods (for example, tularemia). And in this case, biotic factors are still identified that determine the durable existence of foci of such diseases in natural areas, even those used by humans.

The connection of natural foci of diseases with certain geographical landscapes makes it possible to provide a provisional assessment of possible epidemics. dangers of the territory and carry out preventive measures in advance to protect people's health when it is not possible to examine the area for the presence of natural foci of diseases or, at least, carriers of pathogens. Landscape epidemiology of such diseases is closely related to regional pathology, but regional pathology extends only to certain large administrative parts of the state, while landscape epidemiology focuses on areas of various landscapes, which often extend over several large administrative parts of the country. Determining the territorial distribution of natural foci of diseases becomes especially important, because it is the basis of nosogeography (see) of the corresponding diseases. The doctrine of P. o. human diseases is the key to studying new diseases.

E. N. Pavlovsky.

Natural focal infectious diseases (ID) are diseases in which the source of infection is found in nature. Most often these are warm-blooded wild animals, for some diseases - blood-sucking insects, mainly ticks.

The range of each infection is limited to a certain ecological and geographical area.

Transmission of the pathogen to humans occurs through the bites of infected insects (ticks, fleas, mosquitoes, mosquitoes, etc.); when consuming water or food contaminated by sick animals; through household items; in direct contact - contact with the pathogen. 1

Domestic scientists: I. A. Deminsky (1864–1912); the first President of the Ukrainian Academy of Sciences D.K. Zabolotny (1866–1929), N.N. Klodnitsky (1868–1939) and others - made a major contribution to the study of the epidemiology and clinical manifestations of these diseases. In the middle of the 20th century. Soviet scientists carried out enormous expeditionary work to study tick-borne taiga encephalitis, as well as Far Eastern hemorrhagic nephrosonephritis, now called hemorrhagic fever with renal syndrome (HFRS). Young, passionate researchers, passionate about science, took part in these expeditions. Many of them were the pride of Soviet medical science and became academicians of the USSR Academy of Medical Sciences. 2 Among them were L. A. Zilber (1894–1966), A. A. Smorodintsev (1901–1986), M. P. Chumakov (1909–1993). 3

Plague- a natural focal infection that belongs to the group of especially dangerous (quarantine) infectious diseases. The mortality rate in Asia and Africa ranges from 2.5 to 25.7%; during plague epidemics in the past it reached almost 100%.

In natural foci, the source of infection is rodents and lagomorphs of various species. Natural infection with plague has been registered in almost 250 species of wild animals, from which urban rodents - rats and mice - receive the pathogen. Plague is transmitted to humans by flea bites.

The epidemiological situation regarding plague in Russia can be considered unstable due to the isolation of the causative agent of the disease from natural foci of infection and the real danger of importing plague from abroad.

On the territory of Russia, 11 permanent foci of plague have been registered, differing in the types of main carriers of the pathogen: gopher type - Caspian northwestern steppe, Dagestan plain-foothill, Volga-Ural steppe, Central Caucasian high-mountain, Transbaikal steppe, Tuva mountain-steppe, Terek-Sunzha steppe; sand-type - Caspian, Volga-Ural; the field-type - Dagestan high-mountain, and the pika-type - Gorno-Altai high-mountain. The total area of ​​natural plague foci in Russia is over 31 million hectares. The most extensive focal areas are located in the European part of Russia, 10% are in the natural centers of Siberia (Tuva, Transbaikal and Gorno-Altai). To maintain epidemiological well-being during deratization work, one must strive to ensure that the number of rodents in natural plague foci does not exceed 10 individuals per 1 hectare (Kalabukhov N.I., 1947).

In natural foci of the gopher type (Central Caucasus, Caspian steppe, Tuva), plague epizootics among rodents are observed annually, accompanied by the isolation of cultures of the plague microbe. The largest number of the plague pathogen over 16 years of field expeditionary work (from 1979 to 1994) was isolated in the Caspian steppe focus - 4474, in the Central Caucasus and Tuva, respectively, 2765 and 399 cultures of the plague microbe. Foci that had not manifested themselves for a long time became active. Thus, after a 58-year hiatus, plague was detected in the Kursk region of the Stavropol Territory (the territory of the Caspian sandstone focus). In the Dagestan plain-foothill autonomous focus, an epizootic plague among small ground squirrels was discovered in 1994 after a 10-year inter-epizootic period.

In the plague prevention system, epidemiological surveillance is of decisive importance, part of which is monitoring the epizootic state in natural foci of infection. Currently, the arsenal of therapeutic agents used for plague has been significantly expanded. There is no mortality in the bubonic form of plague during antibacterial therapy in modern conditions.

Tularemia. In the recent past, especially during the Great Patriotic War (1941–1945), outbreaks of tularemia were observed in some areas. Due to the widespread prevalence of tularemia, despite the absence of deaths, it posed a danger to the population and military personnel. During the defense of Moscow, tularemia was noted in the Moscow region (G.P. Rudnev). Due to the similarity of the clinical picture with the symptoms of the plague, it was called the “minor plague”. 5

Epizootic and epidemiological features of tularemia are associated with the natural infection of about 125 species of vertebrate animals, mainly representatives of the order of rodents. Among these animals, the most susceptible to the causative agent of tularemia are water rats, hares, muskrats, etc.

The causative agent of tularemia, as well as the causative agent of plague, is transmitted to humans through transmissible, contact, oral and aspiration routes. The vector-borne mechanism of transmission of infection is through ticks (mainly ixodids) and flying blood-sucking dipterans (mosquitoes, horseflies). The preservation of the pathogen and its transmission to humans is carried out with the participation of blood-sucking arthropods, through air and food contaminated with rodent excrement.

Epidemic outbreaks of tularemia can be commercial, with a contact transmission mechanism (harvesting muskrat and water vole skins), through the bite of infected rodents, etc.; agricultural, with an aspiration transmission mechanism (when threshing grain) - through dust contaminated with rodent secretions; production, with contact transmission (processing of agricultural products, slaughtering and cutting of carcasses); household, usually with an oral transmission mechanism - through water and food contaminated with rodent secretions.

The clinical course of tularemia can be acute, protracted and recurrent. According to the classification of G.P. Rudnev, there are: bubonic, ulcerative-bubonic, ocular-bubonic, anginal-bubonic, pulmonary - with predominant damage to the respiratory tract (bronchitis and pneumonic variants), abdominal forms. The generalized form of tularemia develops in weakened patients.

Among those sick with tularemia in Russia, rural residents make up about 1/3, and urban residents make up 2/3. This can be explained by the massive development of suburban areas by city residents (dacha construction, work in gardens and vegetable plots), weak sanitary education work and weakening attention to vaccination against tularemia for people in professions associated with a high risk of contracting this infection.

Leptospirosis are a group of acute infectious diseases caused by leptospira spirochetes with unique biological properties (more than 160 serovars). There are icteric and anicteric forms of the disease.

The main reservoir of Leptospira in nature are various types of small moisture-loving mouse-like rodents: voles, field mice, gray rats. Leptospires are released into the external environment in the urine of animals. People become infected by swimming in open swampy bodies of water, by drinking raw water contaminated with Leptospira, by making hay in swampy meadows, by caring for animals with leptospirosis or who are carriers of Leptospira.

In the spread of leptospirosis, along with mouse-like rodents, farm animals (cattle and small cattle, pigs, horses), game animals (foxes, arctic foxes), domestic and domesticated animals (dogs, cats, deer) play an important role.

A feature of the spread of leptospirosis in recent years is the increased incidence of urban residents compared to rural residents. The epidemiological situation is aggravated by the increase in the number of stray animals, the deterioration of social, economic, and living conditions of the urban population, as well as the free uncontrolled trade in meat and other agricultural food products in cities. In terms of early diagnosis of leptospirosis, attention should be paid to patients hospitalized with a diagnosis of “fever of unknown origin” and with unreasonably suspected “summer flu”.

Leading clinical manifestations: high fever, rash, hepatolienal syndrome; in some of them there is a primary affect (ulcer at the site of pathogen penetration) and regional lymphadenitis.

In recent years, ideas about the distribution, taxonomy and ecology of rickettsia of the tick-borne spotted fever (TSF) group have changed significantly. A number of new rickettsiae have been identified in various regions of the world, many of which claim the status of an independent species, for example, the causative agent of Astrakhan rickettsial fever.

Tick-borne rickettsioses (tick-borne typhus, Siberian typhus, North Asian rickettsiosis) are three of the most important representatives of the LPT group. Active outbreaks that are dangerous to the population are located mainly in the Asian part of Russia (in the forest-steppe regions of Siberia and the Far East). Rickettsial diseases are transmitted to humans through tick bites, mainly Dermacentor, Haemaphysalis. The natural reservoir of the pathogen is small rodents: voles, chipmunks, gophers.

To date, there is no evidence to explain the increase in the incidence of Astrakhan rickettsial fever in the Lower Volga region, but its connection can be traced with an increase in the number of ticks (in particular, dog ticks) in areas with increased concentrations of sulfur-containing compounds in the atmospheric air. There have been quantitative and qualitative changes in the population of the pathogen, its guardians and vectors.

In a short time, the landscape changes and the ecological situation in vast areas deteriorates. Unfavorable environmental changes are occurring on an unprecedented scale.

In modern conditions, it is especially necessary to closely monitor the state of natural foci of infectious diseases both in Russia and abroad.

— an acute viral natural focal infectious disease characterized by damage to the vascular system () and the development of acute renal failure, which can lead to death.
Pathogen: The virus enters the human body through the respiratory tract, gastrointestinal tract and damaged skin.
Sources: mouse-like rodents (bank vole) that excrete the virus in urine and feces, which can infect the environment, food and household items.
: aerogenic (airborne dust), inhalation of dust infected with rodent secretions and nutritional (infected food). (The virus enters the human body through the respiratory tract, gastrointestinal tract and damaged skin).

Leptospirosis

— an acute infectious natural-anthropurgic bacterial disease, the main clinical manifestations of which are symptoms of damage to the vascular system, liver and kidneys, with the development of acute liver or kidney failure.
Pathogens: bacteria of various types that are inherent in certain types of animals - pigs, dogs, rats, etc. Leptospira enters the human body through damaged skin, intact mucous membranes and the gastrointestinal tract.
Sources of infection: in natural conditions - many species of rodents, as well as domestic animals (pigs, cattle, dogs, etc.). Sick animals and carriers release leptospira into the external environment with urine and infect water bodies, food and household items (rodents).
– contact, water, food.

Listeriosis

— acute infectious natural focal bacterial disease, which is characterized by various clinical manifestations: conjunctivitis, lymphadenitis, meningoencephalitis, gastroenteritis, septic condition.
Pathogen- bacterium listeria, an intracellular microorganism. It has the ability to survive and multiply for a long time in soil, water, food products (meat, milk, vegetables) even in cold conditions.
Sources of infection: animals (agricultural, domestic, wild), as well as birds (ornamental and domestic).
infections:

• Food, when consuming infected products;
• Aerogenic, due to inhalation of dust infected by rodents;
• Contact, when communicating with sick animals and infected environmental objects;
• Transplacental, from mother to fetus or newborn (development of septic conditions, death of fetuses and children in the first days of life).

Clinical manifestations of listeriosis are varied - conjunctivitis, lymphadenitis, meningoencephalitis, gastroenteritis, septic conditions.

Pseudotuberculosis

— an acute infectious bacterial disease with a polymorphic clinical picture from scarlet fever, joint damage to foodborne toxic infection and septic conditions.
Sources of infection– various types of rodents.
Pathogen: a bacterium that persists for a long time and multiplies in the external environment and food products (vegetables, fruits, milk, etc.), even in cold conditions.
Transmission routes– food (through infected products) and contact.
The most significant factors in the transmission of infection are food products consumed without heat treatment, which often leads to outbreaks in organized children's groups when the rules for preparing and storing dishes from raw vegetables are violated.

Tularemia

— acute bacterial, natural focal infection. The clinical picture is characterized by the occurrence of unilateral lymphadenitis, conjunctivitis,. The form of the disease depends on the place of penetration of the pathogen into the human body.
Pathogen: bacterium.
Sources of infection: small mammals (rodents and hares, which infect the environment, food products, and household items with their secretions).
Carriers: blood-sucking arthropod insects (horseflies).
Transmission routes: transmissible (bites of blood-sucking insects), contact (infection of intact skin, mucous membranes of the respiratory tract, conjunctiva of the eyes, mucous membranes of the gastrointestinal tract).

Having developed the doctrine of the natural focality of vector-borne diseases of humans and farm animals, he laid the foundations of medical and veterinary biogeography. According to the doctrine of the natural focality of vector-borne diseases, the peculiarity of some diseases is that their pathogens, specific carriers and animals (reservoirs of the pathogen) exist indefinitely in natural conditions (foci) regardless of human habitation. A person becomes infected with pathogens of wild animals by entering temporarily or living permanently in the territory of a natural outbreak. A characteristic feature of such diseases is the presence of natural reservoirs (foci) of pathogens among wild mammals (mainly rodents) and birds. The most pronounced natural focality of vector-borne diseases is in which the spread of infection occurs through blood-sucking arthropods, when the causative agent of the disease circulates along the chain: animal - carrier - animal. Natural foci of vector-borne diseases are confined mainly to the junctions of different types of landscapes, where the largest number of rodents, birds and arthropod vectors are observed; Certain diseases are characterized by certain landscapes: meadows (leptospirosis), steppes (Q fever), savannas (trypanosomiasis), etc. This location makes it possible to predict the possibility of the emergence of vector-borne diseases and organize preventive measures accordingly.

The founder of the doctrine of P. o. human diseases is E.N. Pavlovsky. It gained worldwide fame and recognition. In the Soviet Union, numerous students and followers of E.N. Pavlovsky studied the natural focality of many infectious human diseases.

The existence of natural foci of diseases is due to the continuous circulation of their pathogens among vertebrate animals - most often rodents, birds, as well as ungulates, predators, etc. (sources of infectious agents). The transmission of pathogens from animal to animal, as well as from animal to person, occurs mainly through insects and ticks (carriers of pathogens), however, other routes and factors for the transfer of pathogens are also possible, for example through water, food, contact, etc.

People or domestic animals can become infected with natural focal diseases when entering the territory of a natural outbreak. Infection of people is also possible from domestic animals infected with a natural focal disease.

Natural focal diseases of humans include the following transmissible infectious diseases: dengue, yellow fever, mosquito encephalitis (see Mosquito encephalitis), Saint Louis encephalitis (see Encephalitis), equine encephalomyelitis, plague, visceral and cutaneous leishmaniasis, phlebotomy fever, sleeping disease, Chagas disease, tick-borne encephalitis (see Tick-borne encephalitis), many tick-borne rickettsioses, hemorrhagic fevers, tularemia, tick-borne relapsing fever, Lyme disease.

There are natural foci of rabies, leptospirosis, lobothriasis, paragonimiasis, trichoinosis, schistosomiasis, echinococcosis, etc.

People who enter the territory of a natural outbreak can only get sick if the conditions are present. In the outbreak there must be carriers of pathogens in an active state. Transmission of the pathogen can only occur under certain environmental conditions, which mainly depends on the time of day, climate, landscape features, etc. Thus, most arthropod vectors are active in the warm season, ixodid ticks (carriers of the tick-borne encephalitis virus) are active mainly in the evening , mosquitoes (carriers of the mosquito encephalitis virus) - in the summer-autumn period; reproduction of the mosquito encephalitis virus occurs at temperatures not lower than 21°, infection with it is observed in Southern Primorye in most cases after a hot summer; It is possible to become infected with the plague from marmots only in the warm season, because... In winter, marmots hibernate and stay in a deep hole.

The most susceptible to many natural focal diseases are people who arrived to the focal point from outside, which is taken into account when determining who is subject to immunization.

The most effective measures to prevent natural focal diseases in people are immunization, as well as the use of repellents, wearing protective clothing, using protective nets, disinfestation and deratization in natural outbreaks. Sanitary educational work is of great importance - explaining the need for personal preventive measures to protect against pathogens of certain natural focal diseases during the season of possible infection, especially among people arriving at the outbreak from outside.

Bibliography: Kucheruk V.K. Mammals are carriers of diseases dangerous to humans, in the book: Usp. modern Theriology, ed. V.E. Sokolova, s. 75, M., 1977; Pavlovsky E.N. Natural focality of vector-borne diseases in connection with landscape epidemiology of zooanthroponoses, M. - L., 1964.

Theory of natural focality of infectious diseases

In 1889 D.K. Zabolotny suggested that various types of rodents represent in nature the environment in which plague bacteria persist. Later D.K. Zabolotny (1911) and his students (I.A. Deminsky, 1912, etc.) proved that the keepers of plague pathogens in nature are rodents - marmots, gophers, tarabagans, gerbils, rats, etc.

Since 1938, as a result of numerous studies by academician. E.N. Pavlovsky and collaborators on the etiology and epidemiology of tick-borne encephalitis, endemic rickettsiosis, leishmaniasis, tularemia and other infections developed a coherent doctrine of the natural focality of some vector-borne diseases.

A characteristic feature of this group of diseases is the existence of a natural reservoir of pathogens among wild animals and birds, among which epizootics occur.

The spread of these diseases among the animal world and from animals to humans occurs with the participation of blood-sucking insects and ticks. Thus, the causative agents of these infections continuously circulate in nature along the chain: animal-carrier-animal, and under certain conditions a person is included in the epidemic chain.

So, natural foci of infectious diseases arise and exist for a long time independently of humans as a result of evolutionarily established interspecific relationships between the pathogenic pathogen, the animal body and specific carriers living in certain natural biotopes, i.e. in certain climatic and geographical conditions, with certain flora and fauna.

Infection of a person susceptible to this infection occurs accidentally and this is due to his presence in the territory of a natural outbreak during the period of carrier activity against the background of an emerging epizootic among animals.

So, the existence of a focus is ensured by the presence in it of a pathogen of a susceptible animal and the conditions for their infection (carrier, etc.).

Bloodsucking vectors include ticks, mosquitoes, fleas, lice, etc. Those diseases that are transmitted through vectors are called vector-borne. Thus, for the existence of a focus of a vector-borne infection, three components or a “focal triad” are required: the pathogen, the vector and the warm-blooded host. Transmissible diseases are tick-borne and mosquito-borne (Japanese, etc.) encephalitis, hemorrhagic fevers, tick-borne typhus of North Asia and tsutsugamushi fever and many others. Currently, another group of natural focal diseases is known, the transmission of the infectious principle in which occurs without the participation of a carrier (by contact) during cutting of carcasses, skinning and (or) during an attack and bite of the host animal (rabies, sodoku, etc.) , alimentary through water - anicteric leptospirosis or by airborne droplets, etc. Some cases of infection with tick-borne encephalitis occur when drinking milk from sick (infected) goats, cows; plague, psittacosis, hemorrhagic fevers with renal syndrome, etc. are transmitted by airborne droplets.

In recent years, so-called anthropurgic (man-made) foci have appeared as members of natural foci in territories developed by man within cities, villages and other human settlements (Q fever, yellow fever, Japanese mosquito encephalitis, etc.). This is due to the fact that many mosquitoes feed on humans and domestic animals, then find places where larvae breed in populated areas in various natural and artificial reservoirs, in the basements of houses, in various household utensils, in barrels of water and other places, thus becoming Thus, in synanthropes. Then they suck the blood of domestic animals and rodents infected with pathogens and, attacking a person, infect him.

Outbreaks with hungry infected vectors (ticks - tick-borne encephalitis, tularemia, endemic Lyme borreliosis, etc.) capable of infecting humans and animals are called valence.

Those natural foci in which pathogens of various infectious diseases circulate (tick-borne encephalitis and Lyme disease, plague, tick-borne rickettsiosis and tularemia, etc.) are called conjugate, etiological.

Natural foci are called multivector, in which there are several types of vectors, as in tularemia, endemic rickettsioses (mosquitoes, ticks, horseflies, fly flies, etc.), and if there is only one vector - monovector (mosquito fever).

If in natural foci there is only one type of donor animal, then they are called monohostal, and if there are several donor animals, then such foci are polyhostal, multi-host.

A characteristic epidemiological feature of diseases with natural focality is seasonality, which is determined by the biology of animals - guardians of the infectious principle in natural biotopes (hibernation - in the case of plague) or the activity of carriers. The second epidemiological feature of these diseases is their connection with a certain territory, with certain climatic and geographical conditions (enzootic, endemic). Natural focal infections are characterized by a fan-shaped type of transmission of pathogens. This means that many people become infected at the same time from one donor animal, which most often represents a biological dead end for the pathogen.

The influence of natural conditions is also expressed on the second link of the epidemic process - on the factors of infection transmission.

The natural factor is of particular importance in cases where the carriers are ticks and other arthropods; in addition, the role of the factor in the number of vectors in the development of natural focal infections has long been known; the fewer carriers, the lower the incidence, up to elimination. The role of climatic factor on the development of pathogens in the carrier’s body (temperature) is also known. The great importance of natural processes is also noted in some other infections, the factors of transmission of the infectious principle in which are objects of inanimate nature (water from open reservoirs, contaminated with wastewater, self-purification processes occurring in water, soil, their intensity, etc.). By promoting the rapid development and acceleration of these processes, we help reduce and eliminate gastrointestinal and other infections.