Toxocariasis: an overview

Toxocarosis (Latin toxocarosis) is a chronic tissue helminthiasis caused by the migration of the helminth larva of Toxocara canis in the human body. It is characterized by a recurrent course with internal organs and eyes.

ICD-10 code

B83.0. Visceral migrating larva.

Epidemiology of toxocariasis

Toxocarosis is a zoonosis with an oral transmission mechanism. The source of invasion in a synanthropic focus for humans is dogs that pollute the soil with feces that contain toxocar eggs. People can not be a source of infection, since in the human body adult individuals of the parasite from the larvae are not formed and the eggs are not excreted. Man serves as reservoir, or paratenic, master of toxocar, but in fact he is an "ecological dead end".

The vulnerability of dogs with toxocar varies according to sex, age, the way they are kept, and in almost all areas is very high - up to 40-50% and higher, and in rural areas it can reach 100%. The greatest lesion is noted in puppies aged 1-3 months. Direct contact with dogs does not play a significant role in infecting people. The main prerequisites for the transmission of the pathogen are contamination of the soil with helminth eggs and the contact of people with it. At present, the importance of geophagy in the defeat of children with toxocarosis is proved. Geophagy is an example of direct infection by pathogens of helminthiases without the participation of any other transmission factors, and the person in these cases receives a massive invasion, which, as a rule, predetermines the severe course of the disease. They note a high level of toxicity in the owners of household plots, dacha land plots, vegetable gardens, and people living in yards where they walk dogs, which confirms the role of household contact with the soil when eggs are infected with toxocar. Eggs of toxocar can be transmitted with vegetables and table greens. The transmission factors of toxocar are contaminated animal hair, water, hands. The role of cockroaches in the spread of helminthiosis is established: they eat a significant amount of toxocar eggs and release up to 25% of eggs in the viable state to the environment.

Toksokaroz is common everywhere. They are most often affected by children. A relatively high incidence of some occupational groups is established: veterinarians, communal workers, amateur gardeners. People become infected with toxocarias throughout the year, but more often the infection occurs in the summer-autumn period, when the number of eggs in the soil and contact with it are maximal.

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]

What causes toxocariasis?

Toxocarosis is caused by a dogworm, which belongs to the type Nemathelminthes, the class Nematodes, the suborder Ascaridata, the genus Toxocara. T. Canis - dioecious nematodes, sexually mature specimens of which reach relatively large sizes (female length 9-18 cm, male 5-10 cm). Eggs of Toksokara are spherical in shape, 65-75 microns in size. T. Canis parasitizes in dogs and other representatives of the canine family.

In the life cycle of this helminth, the development cycles-the main and the two auxiliary ones-are singled out. The main cycle of development of toxocar corresponds to the "dog-soil-dog" scheme. After infection of the dog by alimentary tract, larvae leave the eggs in its small intestine and then migrate. The migration of ascarids in the human body is similar. After maturing females toxocar in the small intestine, the dog with feces begins to secrete the eggs of the parasite. This type of helminth development occurs in puppies under 2 months of age. In adult animals, larvae of the helminth migrate to various organs and tissues. Where granules form around them. In them, larvae for a long time remain viable, do not develop, but periodically can resume migration.

Pathogenesis of toxocariasis

T. Canis is an alien helminthic pathogen, the larvae of which never turn into adult individuals. It is the causative agent of helminthiasis of animals, capable of parasitizing a person in the migratory (larval) stage and causing a disease called "Visceral pаrvа migrans" syndrome . The syndrome is characterized by a long-term recurrent course and multiple-organ lesions of an allergic nature. In the human body, as in other parthenic hosts, the cycles of development and migration are carried out in the following way: from eggs of toxocar caught in the mouth, and then into the stomach and small intestine, larvae emerge, which through the mucous oolochku penetrate into the blood vessels and through the portal system veins migrate to the liver, somewhere some of them settle; they are surrounded by an inflammatory infiltrate, and granulomas are formed.

What symptoms does toxocarosis have?

In terms of the severity of clinical manifestations, distinguish toxocarias manifest and asymptomatic, and in the course of the course - acute and chronic.

Visceral toxocariosis affects both children and adults, but in children this form is more common, especially at the age of 1.5 to 6 years. The clinical picture of toxocarias is not very specific and resembles the clinical symptoms of the acute phase of other helminthiases. The main clinical manifestations of acute toxocarias are recurrent fever, pulmonary syndrome, enlargement of liver size, polyadenopathy. Skin manifestations, eosinophilia of the blood. Hypergammaglobulinemia. In children, toxocarosis often develops suddenly or after a short prodromal period. Body temperature is often subfebrile (in severe cases of infestation - febrile), more pronounced in the period of pulmonary manifestations. A variety of types of relapsing rashes on the skin (erythematous, urticaria) are noted. Possibly the development of edema Quincke, the syndrome of Maskl-Wells, etc. Skin syndrome can persist for a long time, sometimes it is the main clinical manifestation of the disease. Examination for children with a diagnosis of eczema, carried out in the Netherlands, showed that 13.2% of them have high titres of specific antibodies to toxocaram. Most of the infected, especially in children, have moderately increased peripheral lymph nodes.

How is Toxocarosis Diagnosed?

Intravital parasitologic diagnosis of "toxocarosis" is extremely rare and only in the study of biopsy material, when in tissues it is possible to detect and verify larvae of toxocar. The diagnosis is established based on the epidemiological history, clinical symptoms. Consider the presence of persistent long-term eosinophilia, although with eye toxocariasis it is not always found. Indication of the maintenance in the family of a dog or on close contact with dogs, on geophagy indicates a relatively high risk of infection by toxocarosis.

How is Toksokarosis treated?

Toxocarosis does not have a single etiotropic treatment regimen. Apply antinematode drugs: albendazole, mebendazole, diethylcarbamazine. All these anthelmintic drugs are effective against migratory larvae and are not effective against tissue forms found in granulomas of internal organs.

How to prevent toxocariasis?

Toksokaroz can be prevented, if you observe personal hygiene, teach children health skills. Timely examination and deworming of dogs are important. The most effective preimaginal treatment of puppies aged 4-5 weeks, as well as pregnant females. It is necessary to limit the number of neglected dogs, equip special grounds for walking. It is necessary to carry out systematic sanitary-educational work among the population, to report information on possible sources of infestation and ways of transmission. Special attention is required by persons who have contacts with sources of infestation (veterinarians, owners of domestic animals, nursery staff of service dogs, excavators, etc.).