Toxocarosis

TOXOCAROSIS is a helminthic disease caused by an unrelated parasite - toxocara, very similar to human ascarida, a nematode of the family Anisakidae of the genus Tohosaga. The diameter of its larva is 0.02 mm.

Two species of toxocaras are known:

- Tocsocara canis - a helminth that affects members of the dog family (dogs, wolves, foxes, foxes),

- Tochosaga mystax (cati) - helminth of the feline family.

However, toxocarosis, caused by Tocsocara canis, also infects humans. Entry of toxocaras larvae into the human body is an "address error", for the parasite it is death.

According to some authors, in Russia, the number of children infected with toxocarosis is 40-50%. In the USA the Centre for Disease Control annually registers 700-1000 cases of toxocarosis. Unfortunately, there are no such data for Kazakhstan.

Sources of toxocarosis

The source of infestation for humans is dogs that excrete toxocar eggs in their feces, as well as animal hair contaminated with eggs. In the USA, 20% of adult dogs and 95% of puppies are infected with these helminths, and toxocar eggs are found in 10-30% of soil samples from parks and yards.

 

People infected with toxocarosis are not a source of infection, as humans are not a natural host for toxocara, and the pathogens do not reach sexual maturity in the human body.

Route of infection with toxocarosis

Among animals, the mechanism of transmission of the causative agent of toxocarosis is:

- direct (infection by eggs from the environment),

- intrauterine (infection of the foetus with larvae through the placenta),

- transmammary (transmission of larvae with milk).

For humans, the main preconditions for transmission of the causative agent of toxocarosis are contamination of soil with toxocar eggs and contact with it. Other transmission factors can be:

- animal hair,

- contaminated food,

- contaminated water,

- unwashed hands.

The season of human infection with toxocarosis lasts throughout the year, but the maximum number of infections occurs in summer and autumn, when the number of eggs in the soil and contact with it are maximum and soil temperature and humidity are favourable for their development. 

Risk groups for toxocarosis infection:

- children 3-5 years old, intensively contacting with soil, sand;

- veterinarians and employees of dog kennels;

- sellers of vegetable shops;

- owners of homestead plots, vegetable gardens;

- persons engaged in hunting with dogs.

Forms of existence of toxocarosis pathogens

Infection of humans occurs when invasive eggs of toxocara enter the intestine. In the proximal small intestine, larvae emerge from the eggs, which penetrate the bloodstream through the mucosa, then enter the liver and the right side of the heart.

Once in the pulmonary artery, toxocar larvae continue their migration and pass from capillaries to the pulmonary vein, reach the left side of the heart and then spread by blood to different organs and tissues. Migrating, they reach the place where the diameter of the vessel does not allow them to pass, and here the toxocar larvae leave the bloodstream, settling in the liver, lungs, heart, kidneys, pancreas, brain, eyes and other organs and tissues.

They remain viability for a long time (months, years). The larvae of the causative agent of toxocarosis, settled in tissues, remain in a "dormant" state, and then under the influence of favourable factors are activated and continue migration.

Over time, some of the larvae encapsulate and are gradually destroyed inside the capsule.

The larva of the causative agent of toxocarosis in the human body can survive for up to 10 years.

Adult toxocaras localise in the small intestine of their hosts.

The average lifespan of sexually mature individuals of Tocsocara canis is 4 months, maximum - 6 months. The female Tocsocara canis lays more than 200 thousand eggs per day, which are released into the environment immature and non-invasive. The maturation period of eggs depends on ambient temperature and humidity, and they remain viable and invasive in the soil for a long time.

Symptoms of toxocarosis

Toxocarosis is characterised by a severe, prolonged and recurrent course (from several months to several years), which is associated with periodic resumption of migration of toxocar larvae. Clinical manifestations of toxocarosis depend on the intensity of infection, larvae distribution in certain organs, the degree of immune response of the host.

Depending on the predominant symptoms are distinguished:

- cutaneous form of toxocarosis,

- visceral toxocarosis,

- neurological form of toxocarosis,

- ocular form of toxocarosis.

Cutaneous form of toxocarosis is manifested by various kinds of allergic reactions on the skin in the form of redness and itching, urticaria, oedema, up to eczema, especially along the course of larvae migration.

Visceral toxocarosis is caused by infection with a large number of larvae. Visceral toxocarosis affects children more often than adults. The main symptoms are:

- recurrent fever,

- pulmonary syndrome (dry cough, frequent attacks of nocturnal cough, severe dyspnoea with asthmatic breathing and cyanosis),

- increased liver size,

- abdominal syndrome (abdominal pain and bloating, nausea, sometimes vomiting, diarrhoea),

- lymphadenopathy,

- eosinophilia, hypergammaglobulinaemia in blood.

An examination of children in New York showed that children infected with toxocariasis had significant deviations from healthy children in many neuropsychological tests, motor and cognitive function. This made it possible to distinguish the neurological form of toxocarosis. The migration of toxocaras larvae into the brain reveals signs of central nervous system damage in the form of various neurological disorders manifested in behavioural changes:

- hyperactivity,

- difficulty reading,

- attention deficit disorder.

Ocular toxocarosis is associated with infection of a person with a minimal number of larvae. The course of the disease is from several months to several years. Clinically, ocular toxocarosis manifests itself in the form of:

- strabismus,

- decreased vision,

- leucocoria,

- vitreous abscess,

- optic neuritis,

- keratitis.

Almost always only one eye is affected by toxocarosis.

Consequences of toxocarosis for the organism

Migrating in the human body, the larvae of toxocarosis pathogens traumatise tissues, leaving hemorrhages, necroses, inflammatory changes. The parasite dies, having had time to harm a person.

Infection of the optic nerve by toxocara larvae can lead to unilateral blindness.

In visceral toxocarosis there are known cases of severe pneumonias, which were complicated and fatal.

Cases of toxocarosis associated with larval migration to the myocardium and functionally important parts of the central nervous system have been described.

Toxocarosis often produces multiple granulomas in any organ and tissue (liver, lungs, pancreas, myocardium, lymph nodes, brain), with a zone of necrosis in the centre, destroying the organ in question.

Diagnostic methods for toxocarosis

It is difficult to detect migrating larvae of toxocara, and it is rarely possible to identify them in histological sections. Therefore, the main methods in the diagnosis of toxocarosis are immunological, because antibodies to toxocara can be detected and at the larval stage of their parasitisation.

The diagnosis of toxocarosis is also established on the basis of clinical manifestations of the disease, titres of specific anti-toxocarosis antibodies. Indication of a dog in the family or close contact with dogs indicates a relatively high risk of infection with toxocarosis.

The presence of allergy to animal hair is also common in toxocariasis.

Diagnosis of ocular toxocarosis is difficult, as specific antibodies are not detected or are detected in low titres, and eosinophil counts are usually normal or slightly elevated. Occasionally, larvae may be found on ophthalmological examination, e.g. in the optic nerve or macular region.

You can be tested for Toxocarosis in any treatment room of OLYMP СDL branches.

Tags: 

Toxocarosis parasitosis worms