Toxocariasis: routes of infection, symptoms, treatment, prevention

Toxocariasis is a disease ( helminthiasis ) caused by human infection with Toxocara larvae.

 Toxocars

These worms come in two types:

• toxocara dogs,
• toxocara of cats.

In animals, helminths parasitize the small intestine and are similar in appearance and development to human roundworms. The main difference is the presence of wide lateral wings at the head end.

The size of helminths in dogs is 12-19 cm, in cats - 3-7 cm.

In the animal's body, the larva emerges from the egg, develops into a sexually mature region and lays eggs. Eggs released into the external environment mature under favorable conditions within 5 days.

The optimal temperature for egg development is 24-30ºС; sufficient soil and air humidity is required.

In the human body, the larvae cannot develop to a sexually mature area; they move throughout the body, settling in various tissues and organs. The larvae can remain viable for months and years.

In places where they parasitize, they cause inflammation.

Children aged 1.5 to 10 years are most often infected.

Humans most often become infected with canine toxocara; infections with cat toxocara are extremely rare.

Toxocariasis

Infection with Toxocara is widespread among animals and humans. The reasons for this are:

• increase in the number of dogs in urban areas,
• high fertility of helminths,
• stability of Toxocara eggs in the external environment.

An increase in the disease is recorded every year, especially in children in rural areas.

The source of infection is dogs (less often cats), which infect the soil with helminth eggs. People cannot be a source of infection, since the parasite remains in the larval stage in the human body.

Ways of infection in dogs

Dogs can become infected with worms in several ways:

• intrauterine infection of puppies in a pregnant bitch,
• through the milk of a nursing dog,
• dogs ingesting mature Toxocara eggs from contaminated soil,
• a dog eating animal tissues infected with Toxocara larvae.

Routes of human infection

1. Small children who come into contact with soil and dogs are more often infected with toxocara.
   Especially often - children suffering from geophagia (who love to eat soil).
2. Anyone can become infected by consuming contaminated food and water.
3. Veterinarians, nursery workers, circuses, zoos, utility workers, grocery store sellers, vegetable store workers, owners of personal plots and pets are at increased risk of infection.

Development of the disease

Helminth eggs enter the human intestine, where larvae 0.1-0.2 mm in size emerge from them.
Some of them penetrate the intestinal wall and are carried through the lymphatic and blood vessels to all organs and tissues:

• liver,
• lungs,
• eyes,
• spleen,
• skeletal muscles,
• brain.

Once settled in the organ, they can remain there for months and years. Gradually the larvae become encapsulated and die. However, when the body’s defenses are weakened, the activation of larvae in the organ and their further spread throughout the body is possible.

When worms encapsulate in organs and tissues, granulomas form around them. In the center of the granuloma there is a focus of necrosis, along the periphery there is a large number of eosinophils, histiocytes, neutrophils, macrophages, lymphoid and epithelioid cells.

Numerous granulomas are found

• in the liver,
• in the lungs
• in the pancreas,
• in the myocardium,
• in the lymph nodes of the abdominal cavity,
• in the brain
• In eyes.

When moving throughout the body, the larvae injure tissues, cause hemorrhages, inflammation, and can become conductors of pathogenic microorganisms.

Parasitization of larvae causes immune responses, which can be expressed as allergic reactions, causing the formation of blood clots and granulomas.

Symptoms of toxocariasis

There are two forms of toxocariasis:

• visceral (infection of internal organs),
• ocular (infection with eye larvae).

The visceral form is more common in children; adults get sick less often and more easily.

The disease can occur in acute and chronic forms.

As a rule, toxocariasis begins acutely.

Symptoms of the acute stage

1. At this stage, a person's body temperature rises. Moreover, the temperature is often subfebrile, usually rises at noon or in the evening, accompanied by chilling, and when it decreases, profuse sweating.
2. There is an increase in lymph nodes.
3. The disease may be similar to pneumonia, with coughing and wheezing.
4. Rashes appear on the skin in the form of hives or rashes.
5. Quincke's edema is possible.
6. The examination reveals an enlargement of the liver, less often the spleen.

Damage to the bronchopulmonary system

When the bronchopulmonary system is affected (registered in 20-50% of patients), eosinophilic pneumonia develops, which is manifested by the following symptoms:

• coughing attacks, more often at night,
• attacks of suffocation with severe shortness of breath,
• blue lips

The doctor listens for dry, wheezing rales, and sometimes pockets of wet rales.

In the blood - hyperleukocytosis and hypereosinophilia.

X-ray examination shows:

• volatile infiltrates,
• pneumonia,
• strengthening of the pulmonary pattern,
• changes in the lungs.

When examining the function of external respiration, signs of broncho-obstruction are revealed.

Damage to the abdominal organs

In 60% of children, toxocariasis occurs with damage to the abdominal organs - intestines, liver, gall bladder.

This form of helminth infection is characterized by symptoms such as:

• loss of appetite,
• weight loss,
• stomach ache,
• nausea,
• vomit,
• flatulence,
• diarrhea (diarrhea),
• enlarged lymph nodes,
• tachycardia.

A typical sign is an enlarged liver, sometimes an enlarged spleen.

Tachycardia and other symptoms of heart damage (dullness of heart rhythms, systolic murmur, expansion of the boundaries of the heart) can be caused by two reasons:

• directly by myocardial damage due to migration of larvae,
• allergic reactions of the body to Toxocar antigens.

Chronic toxocariasis

The chronic stage can last for months to several years with periods of exacerbations. Sometimes, with severe damage to the myocardium, central nervous system and lungs, death is possible.

Asymptomatic toxocariasis

This type of disease can be detected during examination of the patient:

• in a blood test it is manifested by a short-term increase in anti-toxocariasis antibodies in low titers and eosinophilia with a normal leukocyte count,
• slight enlargement of lymph nodes,
• enlargement of the liver by 1-2 cm.

Ocular form of toxocariasis

This form is rarely combined with visceral (with damage to internal organs) and develops mainly in children over 12 years of age and adults.

When severe, it progresses to retinal detachment and can lead to blindness.

Diagnostics

It is difficult to detect Toxocara larvae in the human body. This is due to the fact that there are no methods for isolating migrating larvae and the difficulty of identifying them in histological sections.

Therefore, recommendations for the examination have been developed. Diagnostics is carried out sequentially in four stages.

Stage 1 is to identify indications for examination.
These indications are:

• increased levels of eosinophils in peripheral blood,
• acute respiratory disease (bronchitis, pneumonia, tracheitis), occurring with hypereosinophilia,
• persistent respiratory diseases with hypereosinophilia,
• constant abdominal pain with deterioration of general condition with an increased content of eosinophils in the peripheral blood,
• allergic diseases with increased levels of eosinophils in the peripheral blood and/or increased levels of IgE.

Stage 2 . Assessment of the epidemiological situation. At this stage, epidemiological factors are identified that indicate possible infection with toxocariasis:

• the presence of a dog in the house or on a personal plot (taking into account the gender of the dog, age, presence of puppies, walking characteristics, anti-parasitic treatment),
• presence of a vegetable garden near housing,
• did the sick person eat soil?
• child playing in the sandbox and other contacts with the ground,
• eating unwashed berries, vegetables, fruits.

Stage 3 . Clinical examination of the patient. Based on clinical experience, doctors have developed a table for assessing symptoms and laboratory signs for toxocariasis. The diagnosis is considered valid if there are symptoms and indicators in the amount exceeding 12 points.

Stage 4 .
Serological diagnosis. This method is leading in the diagnosis of toxocariasis. A titer of 1:800 or higher is diagnostically significant for visceral toxocariasis (using ELISA), and 1:400 or higher for ocular toxocariasis.

Treatment

For asymptomatic toxocariasis, no treatment is carried out. Patients should be observed by a doctor.

Children under 3 years of age and patients with severe forms of infection are treated only in a hospital.

Before treatment, the following studies must be performed:

• clinical blood test,
• Analysis of urine,
• ECG,
• blood chemistry.

For treatment, drugs such as:

• albendazole,
• mebendazole.

In addition to these drugs, antisymptomatic medications are prescribed:

• at high temperatures - antipyretics,
• with severe bronchial obstruction - bronchodilators,
• Antihistamines are used to relieve allergic reactions.

If there are clinical and laboratory signs of impaired immunity, before prescribing antiparasitic drugs, a course of immunotropic drugs is recommended (for example, polyoxidonium intramuscularly or rectally after a cleansing enema at night).

Observation by a doctor

After completing the course of treatment, the patient must be under the supervision of a doctor (infectious disease specialist, pediatrician, therapist) for a year.

During this year:

• examination of the patient - once every 2 months,
• clinical blood test - monthly,
• blood test for toxocariasis 4 times a year,
• study of external respiration function (in pulmonary form) - according to indications,
• consultation with an allergist - if necessary.

Prevention

To prevent infection with worms you must:

• If you have a dog at home, deworm it,
• wash hands after contact with soil and animals,
• wash fruits, vegetables, berries,
• If there is a sandbox on your personal plot, protect it with shields or film from animals.