Toxocarosis

Infection mechanism

Manifestations of toxocariasis

Diagnostics

Treatment of toxocariasis

Prognosis and prevention

Toxocarosis – a parasitic disease caused by ascaris larvae. It is characterized by a long course and lesions of several internal organs.

Mature forms of toxocar – large dioecious worms, 4-18 cm long, are localized in the stomach and small intestine of animals (dogs). The intensity of infection in dogs can be very high, especially in young animals. The average lifespan of sexually mature individuals is 4 months, the maximum is 6 months. The female parasite lays more than 200 thousand eggs per day. In 1 g of faeces 10000-15000 eggs can be contained, so that millions of eggs fall into the soil, thereby causing a high risk of infection with toxocarosis.

Infection mechanism

The development cycle of the pathogen is as follows: the released eggs of tokokar enter the soil, where, depending on the humidity and temperature of the soil, they ripen in 5-36 days, becoming infectious. The contagiousness of eggs persists in the soil for a long time, in compost for several years.

The life cycle of toxocars is complex. Allocate the main loop and two auxiliary options. The main cycle takes place according to the scheme: the final owner (dogs) – the soil – the final owner (dogs). The auxiliary cycle (option 1) is transplacental, in this case the parasite in the larval stage passes from the pregnant female to the fetus. An infected puppy becomes a functionally full final owner, source of infection.

The auxiliary cycle (option 2) is carried out along the chain: the final owner (dogs) – soil – reservoir owner. The reservoir host may be rodents, pigs, sheep, birds, earthworms. The person also acts as a reservoir host, but is not included in the transmission cycle of infection, being a biological dead end for the parasite. Further development of the pathogen occurs under the condition that the reservoir owner will be eaten by a dog or other final owner.

In humans, the pathogen development cycle, its migration is as follows. From the toxocar eggs trapped in the mouth, then the larvae emerge into the stomach and small intestine, which penetrate the blood vessels through the mucous membrane and migrate through the portal vein system to the liver, where some of them settle and are surrounded by an inflammatory membrane. Part of the larvae in the system of the hepatic veins passes through the liver filter, enters the right heart and through the pulmonary artery into the lungs. In the lungs, part of the larvae is also delayed, and part, after passing through the filter of the lungs, is carried into various organs along a large circle of blood circulation, settling in them. Toksokar larvae can be localized in various organs and tissues – kidneys, muscles, thyroid gland, brain, etc. In the tissues, the larvae remain viable for many years and periodically, under the influence of various factors, resume migration, causing relapses of the disease.

Toxocarosis is a widespread disease, it is registered in many countries.

The main source of infection for humans are dogs, especially puppies. Infection with toxocarosis occurs through direct contact with an infected animal, the wool of which is contaminated with eggs, or when the ground in which there were eggs of toxocar gets into the mouth. Children are especially susceptible to infection while playing in the sand or with a dog. Adults become infected through household contact with infectious animals or in the course of their professional activities (veterinarians, dog breeders, public service workers, drivers, excavators, etc.). In humans, infection is also possible when eating raw or poorly processed thermally meat. Cases of infection with toxocarosis when eating lamb liver are described.

Manifestations of toxocariasis

Symptoms of toxocarosis are determined by the intensity of infection, the distribution of larvae in organs and tissues, the characteristics of the human immune response. Manifestations of toxocariasis are not specific and have similarities with other worms.

Toxocarosis usually develops suddenly or after a short precancer manifests itself as a slight indisposition. The temperature appears – low in mild cases and high to 39 ° C and higher, sometimes with chills. There may be skin rashes in the form of   urticaria , sometimes swelling type   Quincke.

In the acute period, there is pulmonary syndrome of varying severity: from mild events to   acute bronchitis, pneumonia , severe asthma attacks. Especially severe pulmonary syndrome occurs in young children. Sometimes there are bouts of abdominal pain.

There are cases of lesions of the thyroid gland, manifested by symptoms of a tumor. When migrating larvae to the brain: persistent headaches, convulsions, paralysis.

In children, the disease is accompanied by weakness, mild irritability, sleep disturbance.

Diagnostics

The most characteristic laboratory indicator of toxocarosis is a high content.   eosinophil in peripheral blood. The relative level of eosinophilia can vary widely, reaching in some cases 70-80% or more. Leukocyte count increases. In the chronic stage of the disease, acute clinical and laboratory symptoms subside. Eosinophil elevation remains the most stable laboratory indicator.

Parasitological diagnosis is rarely established and only by the presence in the tissues of characteristic formations – granulomas and larvae and their identification in the study of biopsy and sectional material. This is possible with a puncture biopsy of the liver, lungs, surgery. Immunological reactions are also used to detect antibodies to toxocar antigens. Usually, ELISAs are used with the secretory-excretory antigen of toxocar larvae of the second age.

The diagnostic titer is considered an antibody titer of 1: 400 and higher (in ELISA). An antibody titer of 1: 400 indicates infection, but not disease. Antibody titer of 1: 800 and higher indicates a disease of toxocariasis. Practice shows that a direct relationship between the level of antibodies and the severity of the clinical manifestations of toxocariasis does not always exist.

Treatment of toxocariasis

Treatment of toxocariasis is not sufficiently developed. Apply mebendazole (vermox), medamin. These drugs are effective against migratory larvae and are not effective enough against tissue forms found in the granulomas of the internal organs.

Vermox (mebendazole) is prescribed 200-300 mg per day for 1-4 weeks. Adverse reactions are usually not observed. 

Medamin is used in a dose of 10 mg / kg body weight per day in repeated cycles of 10-14 days.

Albendazole is prescribed in a dose of 10 mg / kg of body weight per day in two doses (morning-evening) for 7-14 days. In the process of treatment of toxocarosis, control of the blood test and the level of aminotransferases (toxic effect of the drug on the liver) is necessary.

Criteria for the effectiveness of treatment: improvement of the general condition, a gradual decrease in manifestations of toxocariasis, a decrease in the level of eosinophilia and titers of specific antibodies. It should be noted that the effect of treatment is ahead of the positive dynamics of changes in the blood. When relapses of clinical symptoms, persistent eosinophilia and positive immunological reactions are repeated courses of treatment.

Prognosis and prevention

The prognosis for toxocarosis for life is favorable, however, with massive infection and severe damage to internal organs, especially in persons with impaired immunity, death is possible.

Prevention of toxocariasis includes maintaining personal hygiene, teaching children hygiene skills. An important preventive measure is the timely examination and deworming of dogs. The most effective treatment of puppies aged 4-5 weeks, as well as pregnant bitches.

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