Larva migrans (migration of larvae) is a helminthiasis caused by the migration under the skin or into the internal organs of a person of larvae of parasites that are unusual for him. The natural final hosts of such helminths are animals (dogs, cats and others), and in the human body they do not grow to sexually mature individuals. Larva migrans syndrome comes in visceral and cutaneous forms.

Skin syndrome Larva migrans called a complex of symptoms that manifests itself during such migration of larvae under the skin. Most often these are serpiose (winding linear) lesions of the skin, resulting from their movement. Blisters, erythematous rashes (redness as a result of dilated capillaries), and swelling may also occur.

The article is about the cutaneous form, not the visceral one. In the first case, the larvae of roundworms penetrate the skin and move under it, and in the second, the larvae of some tapeworms or roundworms from the intestines migrate through the bloodstream to various organs and tissues, including muscles, eyes, brain, heart, causing certain diseases, such as, .

The infection is transmitted primarily through the feces of dogs and cats on beaches in warm climates.

Reasons

The causative agents of larva migrans cutanea syndrome (Larva migrans cutanea) are:

1. from the family Ancylostomatidae:
   • Ancylostoma braziliense (Brazilian hookworm) - most common in America, hosts - cats and dogs;
   • Ancylostoma tubaeforme – found all over the world, hosts – cats;
   • Ancylostoma caninum – all over the world, especially where there is enough moisture, the owners are dogs;
   • Bunostomum phlebotomum – cattle.

1. Nematodes from the genus Strongyloides:
   • Strongyloides myopotami - their hosts are large and small cattle, pigs, rabbits, rats;
   • Strongyloides westeri – horses, donkeys, possibly pigs;
   • Strongyloides papillosus – sheep and goats.

1. Sometimes (rarely) larva migrans syndrome is also called dermatosis caused by birds from the family Schistosomatidae. This infection is also called “avian schistosomiasis.”

In the vast majority of cases, the cutaneous form of larval migration syndrome is caused by two species of helminths from the genus: Ancylostoma braziliense (Brazilian hookworm) and Ancylostoma tubaeforme.

As a result of the infection, red, very itchy raised areas appear on the skin. Such formations can be very painful and, if you scratch them, it is possible that a secondary bacterial infection may develop.

Symptoms of Larva migrans appear in 40% of cases on the legs, 20% on the buttocks and genitals, and 15% on the abdomen. This is due to the most likely places of penetration of pathogen larvae.

Photo

On the hand and palm
On the finger and hand
On the leg
On the buttocks
A less pronounced manifestation of larva migrans syndrome on the foot of a teenager in the form of a very itchy rash.
A rash on the buttocks of an 18-month-old child caused by migrating larvae. The infection occurred on a beach in Australia.

Diagnostics

The diagnosis is not always easy to establish, since some symptoms are similar to those of scabies or other skin diseases. Scraping from the surface of crusts or papules sometimes makes it possible to identify larvae.

Treatment

Larva migrans syndrome usually goes away on its own within a few weeks or months, but a case has been reported that lasted up to one year.

Both general and local therapy are carried out. Treatment includes the use of anthelmintic drugs (,), which are recommended for oral administration. The doctor may also recommend lubricating the affected areas with 10% solutions of iodine in alcohol (5%), phenol or ether.

To relieve itching, it is recommended to use special tablets or creams. Another treatment method is mechanical action. The affected areas are lubricated with petroleum jelly, and then the larvae are removed through the wound using a needle or by cutting the skin. This operation must be performed by a doctor.

If you choose the right treatment, the symptoms of larva migrans can disappear after 48 hours.

Prevention

For prevention purposes, it is recommended to wear shoes in places where there is a high risk of infection. It is advisable to avoid contact with contaminated soil. In some endemic areas, walking dogs on beaches is prohibited. You should avoid swimming in freshwater bodies of endemic areas and contact with untreated thermal water.

In April 2017, Minsk resident Lyudmila was on vacation with her son and friends in Malaysia on the island of Langkawi. She returned home rested, but with an incomprehensible itchy rash on her back. Only almost a month later we managed to find out what it was. At the same time, the rash on the back grew in the form of a thin curved path, it seemed as if someone was crawling in the skin.

The photograph is for illustrative purposes only. Photo: Reuters

A larva entered a body on a beach in Malaysia

Before traveling to Malaysia, Lyudmila studied information about the country and knew that there were a lot of mosquitoes there.

“There really are a lot of them, but they are small and absolutely invisible, you can’t hear them.” You need to use special sprays throughout the day; if you forget, you can wake up in the morning with small pimples after mosquito bites. We were prepared for mosquitoes, but not for what started towards the end of the trip. On the side, along the line where the top of the swimsuit goes, I had a small pimple, like a mosquito bite, it itched all the time, and right away I didn’t attach any importance to it, since there was no particular discomfort. Already on the plane on the way home, my side began to itch unbearably,” says Lyudmila.

Upon arrival, she began to lubricate her body with ointment against skin irritation, but it got worse.

“It seemed to me that I scratched this pimple so much that there was a reaction.” There was nothing left to do but go to the doctor. They prescribed me an ointment, suggesting that by scratching I had introduced some kind of infection into the skin. But the ointment didn't help.

Lyudmila contacted many specialists from public and private clinics. Doctors assumed that she had herpes zoster, and the symptoms really resembled it. When the treatment didn't help, they thought it might be an allergy. But the disease did not go away, and Lyudmila only got worse.

- The further it went, the worse it was. Moreover, the itching grew all the time, my body itched, all I did was smear the redness with brilliant green and apply ice to the itchy places. The cold relieved this itch. The medications prescribed by the doctors did not help, and due to the rash and itching, I could not think about anything else.

Such a curved path appeared on Lyudmila’s back. The disease was accompanied by severe itching and rash.

A month later, Lyudmila was lucky enough to find an infectious disease doctor who made the correct diagnosis. It turned out that she had cutaneous larva migrans, which Lyudmila contracted on the beach in Malaysia. On April 26, she flew back from vacation, and on May 24, she found out what had happened to her.

“It turned out that all this time I had a larva crawling in my skin, and after the doctor’s report, I took an anti-worm pill, and literally after a few hours I felt better.

According to Lyudmila, she could have picked up the larva on the beach in the sand. And although she did not lie on the sand, it suggests that the sand ended up under the swimsuit, and thus the sand larva penetrated the skin.

— In Malaysia, I noticed that tourists mostly do not lie on the sand; for this they use special wooden floorings. Vacationers who came from the post-Soviet space are lying on the sand.

“The larvae of animal worms do not penetrate into the blood and internal organs of humans”

Migratory cutaneous larva is the most common disease that Belarusians bring from tropical countries. Marina Ivanova, Associate Professor of the Department of Infectious Diseases of the Belarusian State Medical University, Candidate of Medical Sciences, says that every year several people complain about skin lesions, and the reason is the larva.

— Where can you most often become infected with migrating larvae?

— In the countries of Southeast Asia, Thailand, Indonesia, migrating larvae were brought from Vietnam, India and Sri Lanka.

— What are the symptoms of a migrating larva?

— Redness on the skin, itching, a feeling of movement in the skin, as the larva moves in the skin at a distance of 1 to 3 cm per day. A curved irregular path appears on the skin, and sometimes bubbles appear. It's unpleasant and scary.

-Who is the carrier of this larva?

— The cause of this disease is the penetration of the larvae of certain helminths (worms) into the human body. These helminths are related only to animals, namely dogs. When dogs run along the beach, they excrete helminth eggs in their feces. Larvae emerge from eggs in the sand. They are invisible to the eye, so there is no need to look at the sand and look for them. They wait for contact with unprotected human skin, for example, when a person walks barefoot along the beach, and they themselves actively penetrate the body. Therefore, the most important advice to tourists: always, no matter what, use beach shoes and do not lie down on the sand. The larvae penetrate through the part of the skin that comes into contact with the sand.

— Can cats be carriers of such helminth larvae?

- No. Cats and dogs are completely different animals both in pathogens and in lifestyle.

— Among the countries where you can most often become infected with migratory larvae, there is no country as popular among tourists as Egypt. Why?

— In order for a larva to emerge from an egg, certain conditions must exist. It should be dark, warm and humid. If such conditions do not exist, there will be no larvae on the beach. It requires a warm, humid climate, wet sand, and unprotected human skin. Recent cases of very severe larva migrans have occurred when people used old hotel bedding woven from natural fibers on the beach. They did not dry out, they were saturated with moisture and sand. This is how an infection occurred, and a very serious one at that.

— When a larva enters the human body, does it awaken immediately or does this take some time?

“Unfortunately, symptoms can appear even a month after contact with sand and larvae. Therefore, we always ask travelers to contact infectious disease specialists even after a month if they notice any changes in the skin.

— Can the larvae penetrate the internal organs of the human body or do they move only in the skin?

— These are non-human helminths, so they can only migrate in human skin. They do not penetrate into the blood or internal organs of a person.

— After using drugs, the larvae die in the human body. But do their corpses dissolve or remain in the body forever?

— With special drugs, anthelmintics, we simply shorten the life of the larva. It dies earlier than it could and stops moving in the skin. And the speed of its movement sometimes reaches 3 cm per day. This is scary for an uninitiated person. And after taking the medicine, the larva dies, and the person’s immunity, his internal forces dissolve it, then the inflammation goes away and everything goes to healing. But a person can, for a year, or maybe more, observe changes in the color of the skin in those places where there were traces of the migration of the larvae.

The larvae moved in the skin along the back.

— If a person is not treated, will the larva die on its own in the body?

- Certainly.

- How long does it take for her to die without treatment?

- For some, everything goes away completely in two weeks, for others it lasts a month or even a month and a half. Everything is individual.

— Why does this larva begin to move in the human body?

- She's alive. All living things have a genetically programmed life, so there is a desire to move. She moves in order to get inside a person, but this is a foreign organism to her, so she cannot pass.

— Besides migrating larvae, what else is often brought from tropical countries?

— Recently, dengue fever has begun to be brought in; it is widespread in the world. This is a viral disease, it does not threaten human life and occurs like the flu, only without affecting the upper respiratory tract, there is a rash, and spots are visible on the skin. This disease is treated with symptomatic medications.

Another imported disease is malaria, but it is rarely imported. Moreover, they are brought not from resort areas, which in this sense are less dangerous, but from trips for work. Malaria and Dengue fever are transmitted through the saliva of blood-sucking mosquitoes.

— Is there a vaccine against these diseases?

— There is no widespread vaccination against Dengue fever; we do not have a vaccine, although it has been developed and used with WHO permission in Mexico. We are waiting for vaccine material to appear here too.

Unfortunately, attempts to create an effective malaria vaccine have been ineffective for almost 70 years. WHO is waiting for the results of the latest trial of one of the vaccines. But now the only way to prevent malaria is to take special anti-malarial drugs before departure, throughout the trip and for another four weeks upon return.

A common disease among travelers returning from tropical countries.
Accurate morbidity unknown in the United States because the disease is not recorded. A CDC survey found that 35-52% of dogs in animal shelters are infected with worms that can cause disease in humans. Cutaneous larva migrans is the second most common helminthic infection.
In our country, the infection occurs primarily in Florida and the Gulf Coast.
Children get sick more often than adults.

Caused by blood-sucking nematodes (crooked heads) present in dogs and cats, for example, Ancylostorna braziliense, Ancylostoma caniurri.
Eggs worms transmitted through the excrement of dogs and cats.
The larvae hatch in moist, warm sand/soil.
During the infection stage, the larvae penetrate the skin.

Diagnosis of cutaneous larvae migrans

Diagnosis of cutaneous larva migrans is established on the basis of anamnesis and clinical picture.
Serpiginous or linear reddish-brown burrows raised above the surface, 1-5 cm long.
Strong .
Symptoms continue for several weeks or months.
Lower extremities, particularly feet (73%), buttocks (13-18%) and abdomen (16%)
Not shown. In rare cases, blood tests may reveal eosinophilia or increased levels of immunoglobulin E.

Differential diagnosis of cutaneous migratory larvae

In cases of infection cutaneous larva migrans The following diseases are often mistakenly assumed:
Skin fungal infections. The lesions present as characteristically scaly plaques and ring-shaped patches with central resolution. If the serpiginous tract of the cutaneous larva migrans is ring-shaped, dermatophytosis is often incorrectly assumed.
Contact dermatitis. The difference lies in the location of the lesions, the presence of vesicles and the absence of classic serpiginous tracts.

Erythema migrans in Lyme disease. The lesions are usually ring-shaped spots or plaques, but are not serpiginous in shape and are not raised above the skin surface.
Phytophotodermatitis. In the acute phase, phytophotodermatitis is manifested by swelling and vesicles, later foci of post-inflammatory hyperpigmentation appear. Such outbreaks can occur after visiting the beach, but they are not caused by sand infested with larvae, but by preparing drinks with lime juice.

Treatment of cutaneous larva migrans infestations

Thiabendazole oral is the only drug approved by the Federal Drug Administration for the treatment of patients with cutaneous larva migrans.
From 500 mg tablets you can prepare a topical cream (15%) on a water-soluble base. There have been few trials of the effectiveness of systemic and topical dosage forms, dating back to the 1960s.
The cream is a good choice for children who cannot swallow tablets. - The recommended oral dose is 25 mg/kg every 12 hours for 2-5 days (the dose should not exceed 3 g per day). The cream is applied topically 2-3 times a day for five days to the larval passages, covering 2-3 cm of skin above the lesions.
- Efficiency is 75-89% with systemic therapy and 96-98% with local treatment.
- Systemic therapy is slightly less well tolerated; adverse reactions include nausea (49%), vomiting (16%) and headache (7%). No side effects were noted for topical medications.

Ivermectin(stromectol) (not approved by the Federal Drug Administration for this use).
- A single dose of 0.2 mg/kg (12-24 mg) is recommended.
- Efficiency with a single dose is 100%.
- In a series of six trials, no side effects were noted.
- Many experts consider this drug to be the drug of choice.

Albendazole has been successfully prescribed for over 25 years, but is also not approved by the Federal Drug Administration for this use.
- The recommended dose is 400-800 mg per day for 3-5 days.
- Efficiency exceeds 92%.
- A dose of 800 mg is used daily for three days or more; gastrointestinal side effects may occur in 27% of patients.

Cryotherapy ineffective and even harmful and should be avoided.
Antihistamines can relieve itching.
If a secondary infection occurs, antibiotics must be prescribed.

Children's sandboxes must be protected from animals.
For pet owners: Keep pets away from beaches, treat them for deworming if necessary, and properly clean up excrement.
Observation is necessary for persistent lesions.

Clinical example of cutaneous larvae migrans. The mother of an 18-month-old boy consulted a doctor about an itchy rash on the child's feet and buttocks. The doctor who examined the boy for the first time made an erroneous diagnosis of dermatophytosis of smooth skin. Treatment with clotrimazole cream was unsuccessful. The child could not sleep due to constant itching and lost weight due to deterioration of appetite. He was admitted to the intensive care unit, where the attending physician discovered that before his first visit to the doctor, the family had returned from a trip to the Caribbean. The child played on the beaches, where local dogs often ran. The physician recognized the serpiginous pattern of cutaneous larva migrans eruptions and successfully treated the child with topical thiabendazole.

Cutaneous larva migrans (creeping rash)

Etiology. Ancylostoma brasiliense usually reaches sexual maturity only in dogs and cats. The larvae, emerging from eggs released in feces, reach the filariform stage and have the ability to penetrate the skin. In humans, the larvae reside in the skin and migrate, resulting in the formation of erythematous tracts visible on the surface of the skin.

Epidemiology and distribution. The spread of helminthiasis among people requires appropriate conditions: ambient temperature and humidity for the development of eggs to the stage of infective filariform larvae. Beaches and other wet, sandy areas are high-risk areas because animals choose these areas to defecate, and A. brasiliense eggs develop well in such soil. In the United States, the disease has been reported in the southern states along the Atlantic coast and the Gulf of Mexico.

Places of skin penetration by larvae become noticeable a few hours after their penetration. The migration of larvae in the skin is accompanied by severe itching. Scratching can lead to bacterial infection. Within 1 week, random erythematous, linear elements develop from the primary red papule, the length of which can reach 15-20 cm. If untreated, the larvae can remain viable for several weeks and months.

Loeffler's syndrome was observed in 26 of 52 cases of creeping rash. Transient volatile pulmonary infiltrates accompanied by increased numbers of eosinophils in the blood and sputum were interpreted as an allergic reaction to helminth infestation, but it may have been a reflection of pulmonary migration of larvae.

Laboratory data. Eosinophils are found in the skin elements, but eosinophilic leukocytosis is moderate, except in cases of Loeffler's syndrome. The percentage of eosinophils in the blood can increase up to 50%, in sputum up to 90%. Larvae are found on skin biopsy only in rare cases.

Treatment. The best drug is thiabendazole; it should be given orally at the dose suggested for the treatment of strongyloidiasis (see below). If necessary, treatment can be repeated. The drug can be used topically as a 10% aqueous suspension. Local application avoids the general toxicity of the drug. Superficial bacterial infections are suppressed by using moist dressings and elevating the limb. For intense itching, oral antihistamines are recommended.

Forecast. If left untreated, the disease lasts several months. Treatment is usually successful.

Prevention. It is necessary to prevent dogs and cats from contaminating recreational areas and children's play areas.

Trichostrongylosis

Definition. Trichonstrongylidosis is a worldwide intestinal helminthiasis of herbivores. A person can be considered as an accidental host.

Etiology. Almost a dozen species of trichostrongylids are known to infect humans. The disease is typically widespread in Asia, the Middle East and South America, but rare cases of human infection have been reported in the United States. Due to the high incidence of infection in animals in the United States, the low incidence of infection in humans there is not entirely clear. It is possible that some of these infestations are mistaken for hookworm infections.

The eggs are similar to hookworm eggs, but are longer, have sharper ends, and are at later stages of development (16-32 blastomeres) when found in fresh fecal samples.

Pathogenesis. Infection occurs by consuming green leaves of plants contaminated with stage III larvae. Upon reaching the small intestine, they attach to the mucous membrane and develop into adults within 4 weeks. Adult helminths feed on blood and remain in the intestines for a long period of time. According to Sandground, in the experience of self-infection, the disease lasted more than 8 years.

Clinical manifestations. In most cases, helminthiasis is asymptomatic, but intense infestations can cause discomfort in the epigastric area and anemia. The significance of trichostrongylids lies mainly in the fact that their eggs are similar to those of hookworms. Moreover, since trichostrongylides are resistant to some anthelmintics effective against hookworms, it may be erroneously assumed that drug-resistant cases of hookworm disease exist.

Laboratory diagnostics. Diagnosis depends on detection of eggs in feces. Due to their scarcity, they are usually only detected using an enrichment method. In the case of manifest invasions, leukocytosis with significant eosinophilia (up to 80%) may occur.

Treatment. Treatment with tetrachlorethylene is ineffective. For manifest infections, thiabendazole is indicated at a dose of 25 mg/kg 2 times a day for 2-3 days or pyrantel pamoate according to the regimen used for hookworm infections. Both of these drugs are classified by the US Food and Drug Administration as undergoing clinical trials for this infection.

Prevention. In endemic areas, plant leaves must be cooked before being eaten.

Strongyloidiasis

Epidemiology. Most often, infection occurs when larvae penetrate the skin. Some cases of infestation may result from ingestion of contaminated food and water, and sometimes the pathogen appears to be transmitted by contact. However, sexual transmission is very rare. Transmission through breastfeeding in humans has been described in cases of S. fuelleborni infection. The disease is endemic in the tropics, where heat, humidity and lack of sanitation contribute to its spread. Sporadic cases have occurred among Puerto Ricans and in rural areas of the southern continental United States. Former British and American soldiers held captive in Southeast Asia during the Second World War were tested for helminths. After 40 years, more than 25% of those examined were found to have this invasion; in most cases the disease manifested itself clinically. Cases of chronic strongyloidiasis have been reported in Vietnam War veterans in the United States.

Laboratory research. Although strongyloidiasis may be suspected based on clinical findings, a definitive diagnosis can only be made through laboratory testing. To avoid confusion with hookworm disease, fresh fecal samples should be examined; Typically, fresh feces contain larvae in strongyloidiasis, while in ancistomiasis they contain eggs. Since the number of larvae in feces is small and fluctuates from day to day, it is necessary to examine several samples using enrichment and culture methods. If the lungs are affected, sputum should be examined for the presence of larvae. The diagnosis can be facilitated by microscopic examination of duodenal contents and jejunal biopsy. Sometimes a thread with a weight at the end is inserted into the patient's duodenum, left there for a while, then removed. Liquid is squeezed out of a piece of thread stained with bile and then examined for the presence of larvae. There is evidence that the reaction of enzyme-labeled antibodies using antigen from intestinal eel larvae gives positive results in approximately 80% of patients and can be used for diagnosis.

Eosinophilic leukocytosis is characteristic, except in very severe cases. When eosinophilia is combined with symptoms of peptic ulcers, strongyloidiasis should be suspected.

Treatment. All infected people must be treated to prevent the development of severe disease. The most effective is thiabendazole, administered orally at a dose of 25 mg/kg 2 times a day for 2-3 days. For disseminated strongyloidiasis, treatment should be continued for 7 days or more. When treated with this drug, patients often complain of dizziness, nausea and vomiting. Delayed release of aminophylline can lead to toxic effects. Hypersensitivity reactions may develop, which can be controlled by the use of antihistamines. Feces should be subjected to control tests at intervals of 3 months, since helminthiasis is not always easily destroyed and repeated treatment may be required.

Forecast. In normal cases, the prognosis is favorable. Since the possibility of hyperinvasion is unpredictable, all measures should be taken to cure each patient with strongyloidiasis. In severe cases with hyperinvasion, the prognosis is poor.

Prevention. In general, the measures are the same as for the fight against hookworm disease. In addition, it is important to remember that infection can be caused by eating contaminated food (especially raw vegetables) or contaminated water, as well as through contact. Persons with a history of residence in an endemic area should be carefully screened for the presence of helminths before treatment with steroids or immunosuppressive drugs is initiated. Because larvae may not be shed in feces, repeat fecal and upper bowel examinations are indicated for a number of weeks after initiation of such therapy. Because the sputum, vomit, feces, and tissue fluids of patients with disseminated disease may contain infective filariae larvae, hospital staff should use gloves and gowns.

Intestinal capillariasis

Definition. Intestinal capillariasis is a human helminthiasis caused by the nematode Capillaria philippiensis. Capillaries were first discovered in 1963 in a seriously ill patient in the Philippines. Infestation manifests itself as intractable diarrhea with a high mortality rate. Clinical study showed the presence of severe enteropathy with protein loss and impaired absorption of fats and carbohydrates.

Epidemiology. The disease has been found almost exclusively in individuals living along the northern and western coasts of Luzon, Philippines. Several cases have also been reported in Thailand. Since 1966, the disease has become an epidemic, with more than 2,000 cases and 100 deaths reported. Men were infected more often than women, possibly due to their occupation. Before the discovery of effective chemotherapy drugs, the mortality rate without treatment was as high as 30%; with the introduction of chemotherapy it was reduced to 6%.

Pathogenesis and clinical manifestations. Adult helminths penetrate the small intestinal mucosa in large numbers and cause severe enteropathy with protein loss and malabsorption. Typically, hypokalemia, hypocalcemia and hypoproteinemia are observed. According to autopsy data, the invasion does not spread beyond the intestine. At the beginning of the disease, rumbling in the abdomen and recurrent vague abdominal pain appear, then, usually after 2-3 weeks, profuse watery diarrhea begins. Other symptoms consistent with underlying pathophysiological processes are anorexia, vomiting, weight loss, muscle wasting and weakness, hyporeflexia and edema. Abdominal tenderness and tension may occur. The period between the onset of symptoms and the death of the patient usually lasts for 2-3 months. No subclinical course of invasion was observed.

Diagnostics. Diagnosis is based on the detection of eggs in feces. Capillary eggs should be differentiated from similar whipworm eggs. It is necessary to take measures not to miss capillariasis in people with trichuriasis, since in the endemic zone, in most patients, both of these invasions can coexist.

Treatment. The use of mebendazole is combined with the administration of fluids and electrolytes, which leads to an improvement in the patient’s condition: 400 mg of the drug per day, divided into several doses, should be prescribed for 20 days to prevent relapses.

CHAPTER 167. TREMATODOSIS

James J. Plorde

Paragonimiasis

Definition. Paragonimiasis (endemic hemoptysis) is a chronic infection of the lungs caused by trematodes of the genus Paragonimus. Clinically, the disease is characterized by cough and hemoptysis. Ectopic helminths may be the cause of some other disorders. The widespread geographical distribution of the disease is probably due to the hermaphroditism of flukes.

Etiology and epidemiology. Most often, the causative agent of human paragonimiasis, especially in the countries of the Far East, is P. westermanii. However, in some cases, the disease can also be caused by other types of trematodes - P. skrjabini, P. heterotremus (China), P. africanus, P. uterobilateralis (Central and Western Africa), P. kellicotti (North America), P. mexicanus, P . ecuadoriensis and R. caliensis (Central and South America). Approximately 1% of persons immigrating to the United States from Indochina were infected with P. westermanii.

Adult helminths have a short, thick body 7-12 mm long and 4-6 mm wide. Their life expectancy in the encysted state in the host's lung parenchyma is about 4-5 years. The eggs are dark golden in color, covered with a shell, 50-90 microns in size, reach the bronchioles, from where they are then coughed up or swallowed with sputum and subsequently excreted in the feces. Once in fresh water, they must undergo final maturation within a few weeks, and only after that they form miracidia.

Infection occurs when a person ingests cysts located in the body of a secondary intermediate host - freshwater crabs, crayfish or shrimp. In the duodenum, metacercariae excyst, penetrate the intestinal wall into the peritoneal cavity, and then migrate through the diaphragm into the lungs. Helminths can also be found in the intestinal wall, liver, pancreas, kidneys, testes, mesentery, skeletal muscles, subcutaneous tissues and the central nervous system, in particular in the brain. In addition to humans, the definitive hosts of flukes are dogs, cats, pigs, rats and wild carnivores. In some of them, young helminths are found in the striated muscles. People can also become infected by eating poorly cooked meat.

The spread of paragonimiasis is facilitated by the lack of food and the uniqueness of local customs. Metacercariae survive in vinegar and weak brine or poorly cooked food and serve as a source of infection among the population of the Far East. Raw crab juice, used to treat measles in Korea and to treat infertility in Cameroon, can also spread the infestation. In endemic areas, children become infected by eating raw crabs while playing.

Pathogenesis and clinical manifestations. An eosinophilic granuloma forms around the adult helminth, which in some cases can lead to the formation of a fibrous cyst. Damaged areas of the pulmonary parenchyma (up to 1 cm in diameter) often communicate with bronchioles, resulting in the development of a secondary bacterial infection. Small fibrous nodules form around the helminth eggs in the lung tissue. Chronic bronchitis and bronchiectasis develop, accompanied by rust-colored sputum and hemoptysis. In severe forms of infection, insufficient removal of infiltrate from the lungs is observed, and abscesses occur. Exudative effusion mixed with eosinophils and cholesterol crystals is observed even in the absence of damage to the lung parenchyma. X-ray findings are determined by the stage of the disease. Initially, diffuse or segmental infiltration with (or without) pleural effusion is observed in the lower or middle fields. Then they are gradually replaced by round-shaped nodules, 2-4 cm in size, sometimes hollow inside. The presence of round cysts, fibrosis, and existing calcification may resemble pulmonary tuberculosis, an infection that often coexists with paragonimiasis.

Intestinal or peritoneal forms of invasion are characterized by the presence of compactions and pain in the abdominal area. Various types of paralysis and epilepsy are observed when the brain is involved in the pathological process. Homonymous hemianopsia, optic nerve atrophy, swelling and inflammation of the optic nerve nipple often develop. Eosinophilic leukocytosis and increased protein content are observed in the cerebrospinal fluid.

In 50% of patients, radiography reveals cerebral calcification. Infestation by P. skrjabini and, possibly, P. ecuadoriensis is characterized by the presence of migrating subcutaneous nodes containing adult helminths.

Laboratory research. A constant sign of invasion is eosinophilia. Diagnosis is based on the detection of characteristic, coated helminth eggs in sputum, feces, pleural fluid or tissue. During the first 3 months, there may be no eggs in the sputum, but subsequently they are found in 75-85% of patients. It should be noted that at a later date, repeated studies using enrichment methods may be required to identify eggs. When staining material using the Ziehl-Neelsen method, used to diagnose tuberculosis, trematode eggs are not detected, since sputum enrichment methods used in the diagnosis of tuberculosis destroy helminth eggs. Since many infected patients suffer from concomitant tuberculosis, paragonimiasis may not be diagnosed in them. In children, helminth eggs are often found when examining feces. In serological studies, the complement fixation reaction (CFR) is used, the results of which correlate well with the degree of activity of the process. Within 6 months after successful treatment, RSC gives a negative result. The skin test did not differentiate invasion from the post-invasion period and is used mainly for epidemiological purposes.

Treatment and prevention. Praziquantel is the most effective. A dose of 75 mg/kg is given in three divided doses over 1 or 2 days. Bithionol can also be used - 30-40 mg/kg in fractional doses daily for 10-15 days. Clinical signs quickly disappear, infiltrates in most cases resolve within 3 months. Side effects are minor and include nausea, vomiting and urticaria. In case of concomitant bacterial infection, appropriate therapy is necessary. Particular attention should be paid to the prevention of superinfestation by the same type of helminth.

The most effective practical measure to combat infestation is the appropriate cooking of food before consumption.

Clonorchiasis

Definition. Clonorchiasis affects the bile ducts and is caused by the trematode Clonorchis sinensis. As a rule, the invasion is asymptomatic, however, in the case of a high degree of infection, phenomena of biliary obstruction may develop.

The larvae are released in the duodenum, enter the common bile duct and migrate to the second-order bile ducts, where they develop into adults within 1 month. In addition to humans, dogs, cats, pigs and rats serve as reservoirs of infection. The main endemic areas are Korea, Japan, Taiwan, Hong Kong, southern China and Vietnam, where in the past clonorchiasis was widespread almost everywhere as a result of the use of human manure and feces in fish farming in reservoirs. Improvement in sanitary and hygienic conditions of human life led to a sharp reduction in the transmission of helminths in most disadvantaged areas, but the infectivity rate of the invasion remained at a fairly high level, which was due to the duration of survival of adult helminths in the human body. 25% of the population of Hong Kong and a small part of immigrants from China were infected. In the United States, infection can occur by eating contaminated dried, frozen, or salted fish imported from the Far East. Clinically, infection manifests itself mainly in the adult population.

Laboratory diagnostics. Preliminary diagnosis of clonorchiasis is based on clinical and epidemiological data. Increased alkaline phosphatase levels and hyperbilirubinemia are possible. The level of eosinophilic leukocytosis fluctuates. Plain radiography of the abdominal cavity reveals calcification of the liver parenchyma, and percutaneous transhepatic cholangiography reveals dilation of the intrahepatic bile ducts. The final diagnosis is determined after the detection of helminth eggs in the patient’s feces or in the contents of the duodenum. The eggs measure 29 µm long and 16 µm wide, have a prominent rim on the shell and a small bulge at the posterior end; they must be differentiated from the eggs of Metagorimus, Heterophyes and Opisthorchis, which presents certain difficulties. Antigen prepared from adult worms can be used to perform a complement fixation test and enzyme-linked immunosorbent assay (ELISA) to determine the host's immune response.

Treatment and prevention. To treat patients with clonorchiasis, praziquantel is used at a dose of 25 mg/kg 3 times a day for 1 day. An effective measure to prevent infection is to eat freshwater fish products only after appropriate heat treatment.

Opisthorchiasis

The main reservoir is cats and wild carnivores, and the distribution area covers the coasts of rivers and lakes rich in fish. According to some reports, about 90% of residents of rural areas in northeast Thailand are carriers of helminths. The clinical manifestations of the invasion resemble those of clonorchiasis, with the exception of cholelithiasis, which is quite rare.

At autopsy, cholangiocarcinoma was detected in 50% of patients. Diagnosis is based on the detection of helminth eggs in feces or duodenal contents. Treatment of patients is the same as for clonorchiasis. An effective measure to prevent invasion is proper cooking of fish.

Fascioliasis

Fascioliasis is a helminthiasis from the group of trematodes caused by hepatic fasciola (Fasciola hepatica), which, like Clonorchis, lives in the bile ducts of the definitive host. The size of a mature helminth is 3 cm in length and 1 cm in width, the eggs are large (length 140 microns, width 70 microns), covered with a shell, and mature in fresh water until larvae form.

Fascioliasis is characterized by the development of red liver in sheep - the main definitive host of the helminth. Helminthiasis is widespread mainly in countries with developed sheep and cattle breeding, but cases of infection are reported in almost all regions of the world. In North America, fascioliasis occurs in the southern and western United States, Central America, the Caribbean islands, and Puerto Rico.

Infection occurs by ingestion of an encysted form of the parasite attached to aquatic edible plants (for example, aquatic lettuce). The larvae excyst in the duodenum, migrate through the intestinal wall, penetrate the peritoneal cavity, penetrate the liver capsule and finally enter the bile ducts, where they reach sexual maturity. Sometimes larvae can migrate and mature in places unusual for them, including the pancreas, subcutaneous tissue, chest or brain.

Diagnosis is based on the detection of eggs in feces or in the contents of the duodenum. Certain difficulties arise when differentiating the eggs of the hepatic fasciola from the eggs of Fasciolopsis buski. For serological diagnosis, the complement fixation reaction, hemagglutination and precipitation reactions are used. A skin test may be used.

Treatment is the same as for clonorchiasis.

In order to prevent helminthiasis, aquatic plants such as water lettuce are not recommended to be consumed, vegetables cultivated in irrigated fields using wastewater should be boiled, and drinking water should be boiled.

Fasciolopsidosis

Fasciolopsidosis is a helminthiasis caused by the intestinal fluke F. buski, which lives in the upper intestine of the definitive host. The main definitive host is the pig. China, Thailand, India and other areas of the Far East are extensive endemic foci of invasion. A person becomes infected by ingesting the larvae of the pathogen in water or aquatic plants. Adult helminths attach to the intestinal mucosa, causing ulcerations. The disease is asymptomatic. In case of severe damage (in the early period), diarrhea, abdominal pain, gastrointestinal bleeding and intestinal obstruction appear. Later, asthenia develops with ascites and dropsy. Diagnosis is based on medical history and detection of eggs in feces. The eggs resemble those of Fasciola hepatica. The prognosis in severe cases, especially in children, is unfavorable. Treatment is carried out with praziquantel, the treatment regimen is the same as for clonorchiasis or hookworm disease.

Heterophyosis and metagonimiasis

Heterophyes heterophyes and Metagonimus yakagawa are small intestinal flukes of humans and other fish-eating mammals. Distributed in the Far East, and Heterophyes - in India, Egypt and Tunisia. Infection occurs by eating infected freshwater fish. Adult worms (2 to 3 mm in size) attach to the lining of the small intestine. With high intensity of invasion, they can cause abdominal pain and/or diarrhea. In some cases, eggs can be localized in the brain, spinal cord or heart, where they cause granulomatous changes. Eggs are usually released into the external environment in feces. Their morphology resembles that of Clonorchis eggs. Treatment is carried out with praziquantel (according to the scheme described for clonorchiasis) or tetrachlorethylene (as described in Chapter 166 for hookworm disease). Since the lifespan of these flukes is about 1 year, treatment is not advisable if there are no symptoms.

CHAPTER 168. CESTODOSES

Most often, the penetration of larvae into the skin occurs in the area of ​​​​the feet and buttocks. Symptoms of larva migrans depend on the progress of the larvae in the upper layers of the dermis, which cause nonspecific dermatitis of a linear filamentous nature up to 3 mm wide with bizarre shapes and weaves. The advancement of the larvae in the skin (up to several centimeters) is accompanied by severe itching and burning, which leads to scratching, sometimes significant, and secondary infection. With the simultaneous penetration of several larvae, the interweaving of the threads of dermatitis becomes especially intricate, however, the area of ​​​​the skin affected always remains limited to a certain extent, the larvae seem to “spin” in one place.

The evolution of a migratory larva is self-limited in time. The duration of stay of the larvae in the skin is very variable and depends on the type of worm. In many cases, the larvae die in the skin within 4 weeks; on the other hand, they are known to persist for several months.