Toxocariasis is a chronic infectious disease caused by the larvae of the toxocara roundworm. The invasion is characterized by fever, recurrent rashes and an increase in the size of the liver. Pathology is accompanied by damage to the eyeballs and internal organs: heart, brain, lungs. Diagnosis consists in the detection of specific antibodies to the pathogen. Etiotropic treatment (anthelmintic drugs), means of symptomatic therapy are also used, in some cases surgical interventions are performed.
ICD 10
B83.0 Visceral form of diseases caused by migration of helminth larvae [visceral Larva migrans]
General information
Toxocariasis refers to helminthiasis associated with the migration of helminth larvae of animals (cats, dogs, foxes). Toxocara was discovered in 1782 by the German scientist Werner, the human disease caused by this helminth has been known since 1950. Helminthiasis is widespread everywhere, the largest number of cases have been registered in France, Spain, Austria, the USA, India, Japan, Korea, Brazil, China and Russia. The seasonality is summer-autumn. The risk group includes children under 6 years of age, which is usually associated with geophagy, utility workers, veterinarians, dog breeders, car mechanics, owners of household plots and diggers.
Causes
The causative agent is the roundworm Toxocara, the most common types of invasions are T. sapis (canine) and T. sati (feline). The main development cycle of the parasite does not include the human body, so people turn out to be accidental hosts of the helminth, which in such conditions is unable to reach a sexually mature form. The source of infection is a sick animal (more often a dog), a sick person is not epidemiologically dangerous. It is believed that the proportion of infected with toxocariasis among adult dogs varies from 15 to 50%, puppies – up to 80%.
Sick animals secrete helminth eggs with feces, the parasites themselves are in a sexually mature form in a permanent host in the digestive tract. Yards, playgrounds, parks are considered the most dangerous, since contamination of the earth with parasite eggs occurs in 10-40% of soil samples. Infection of people occurs by contact and food – by stroking, playing with animals, especially stray ones, eating unwashed berries, fruits and vegetables. It is noted that cockroaches can absorb toxocar eggs, followed by the release of up to 25% of potentially viable individuals, which plays an important role in the spread of infection in everyday life.
Pathogenesis
After the toxocara eggs enter the human small intestine (mainly the duodenum), larvae are released, penetrating into the systemic bloodstream through the mucous membrane. First, toxocars are introduced into the liver and the right half of the heart, then into the pulmonary artery and the left ventricle, from where they exit into the large circulatory circle. Spreading through the body, the larvae settle in various organs and tissues, causing hemorrhagic and necrotic changes, the formation of inflammatory foci in the form of granulomas, in the center of which is necrotic tissue and larva, around – inflammatory infiltrate.
Allergic reactions occur when vital products enter the bloodstream. Some of the larvae die, the remaining helminths secrete a special masking substance that allows them to persist in the body for up to 10 years, periodically migrating through the circulatory system and affecting new tissues. A characteristic feature of toxocars is the formation of granulomas in the pancreas, brain, liver, lungs, myocardium and mesenteric lymph nodes. The pathogenesis of eye damage has not been fully studied, there are hypotheses about low invasion activity and low severity of the immune response.
The pathogenesis of epilepsy in toxocariasis is not completely clear. It is assumed that brain damage can lead to the formation of fibrous scars after acute inflammation or chronic granulomas. Another theory explains the appearance of epileptic seizures when neurons are damaged by the increased formation of pro-inflammatory cytokines due to increased permeability of the blood-brain barrier caused by parasites, as well as autoantibodies to neuronal elements, which are often found in patients with toxocariasis.
Classification
The classification of toxocariasis in humans is based on the depth of invasion into the human body. Helminthiasis almost always occurs with minimal or non-specific clinic (subclinically), the asymptomatic form occurs in 13% of cases of the disease, organ lesions are more characteristic of children. The following types of toxocariasis are distinguished:
- Eye. It is typical for children over 8 years old, teenagers and young adults. The lesion of the visual apparatus is usually unilateral, occurs in the form of chronic endophthalmitis, uveitis, vitreous abscesses, papillitis, keratitis and strabismus. With prolonged course, blindness is possible.
- Visceral. It occurs acutely or chronically with the involvement of the respiratory system, heart, skin, lymph nodes, spleen, liver, joints and muscles. Diarrhea, nausea and vomiting are often observed. Brain lesions are described: recurrent headaches, meningoencephalitis, epileptic seizures.
Symptoms
The incubation period is difficult to determine, it is believed that it can take several years. With an acute onset, fever up to 38.5 ° C and above is observed, respiratory system lesions – from nasal congestion, dry cough and sore throat to severe shortness of breath and asthmatic status. An itchy rash appears on the skin in the form of blisters and spots, with the subcutaneous location of the larvae, straight or sinuous reddish-brown passages raised above the surface are visible. Enlarged dense-elastic painless lymph nodes are often detected in children. Patients with toxocariasis often complain of abdominal pain, nausea, sometimes vomiting and stool breakdowns.
The chronic variant of toxocariasis proceeds with periods of remissions and exacerbations. About 30% of patients report recurrent skin rashes, weight loss, prolonged subfebrility (37-38 ° C) and enlarged lymph nodes. During the period of chronic invasion, there may be pain in the heart area, a feeling of “fading”, palpitations, which indicates a lesion of the heart muscle. There may be pain and restriction of movements in large joints, pallor of the skin and mucous membranes, perversion of taste, rapid fatigue. In children, toxocariasis can manifest itself by slowing down growth and mental development, aggression.
Ocular toxocariasis is accompanied by a gradual deterioration of vision, vision, the appearance of “dots” in front of the eyes, a blind spot in the field of vision (scotomas). In the vast majority of cases, one eye is affected. There is no temperature reaction and intoxication phenomena. Lesions of the nervous system are characterized by increased irritability, hyperactivity, severe headaches, epileptic seizures and paralysis, may occur with severe fever (more than 39 ° C), chills, fatigue, weakness, impaired consciousness, loss of ability to productive contact.
Complications
The most common complications of visceral toxocariasis are bronchial asthma, chronic bronchitis and epilepsy, ocular retinal detachment and unilateral blindness. The subcutaneous location of toxocar larvae leads to the addition of secondary bacterial infection, the formation of infiltrates, abscesses and phlegmon, lung damage leads to severe pneumonia of mixed etiology with increasing respiratory failure. Massive invasion of helminths, multiple organ damage can cause death. In pregnant women, toxocariasis often reveals miscarriage, delay in fetal development.
Diagnostics
The diagnosis of toxocariasis is confirmed by an infectious disease doctor. To exclude a combination of visceral and ocular helminthiasis, an ophthalmologist’s examination is mandatory, according to indications, consultations of other specialists are prescribed. Diagnostic methods necessary for the verification of toxocarous lesions include the following techniques:
- Physical examination. Examination of the skin reveals the presence of urticaria, erythematous rash, lymphadenopathy. Dry and wet wheezing can be heard in the lungs during auscultation. The abdomen is soft, sensitive to palpation, hepatosplenomegaly is often observed. When the brain is affected, meningeal signs are detected.
- Ophthalmological examination. With toxocariasis of the eye, during ophthalmoscopy, toxocar larvae are detected in the vitreous, macula and optic disc region; during examination, the movement of the parasite can be fixed. Exudative vitreal changes are described as “snow balls”, hemorrhages, fibrosis and retinal detachment are often observed.
- Laboratory tests. Blood test with toxocariasis, pronounced leukocytosis, an increase in ESR, and often eosinophilia (6-90%) are observed. With prolonged invasion, anemia is detected. Biochemical parameters are within normal limits, there may be an increase in the activity of ALT, AST, total bilirubin, amylase and creatine phosphokinase, hypoalbuminemia and hypergammaglobulinemia. General analysis of urine without specific changes. Charcot-Leyden crystals can be found in the sputum of patients with pulmonary lesions.
- Identification of infectious agents. The leading method is serological. ELISA with toxocar antigens is considered positive at a titer of 1:400 (invasion), values of 1:800 or more are a sign of visceral form. For an eye lesion, an antibody titer of 1:200 and higher is considered diagnostic, a study of tear fluid is more informative. Confirmation of the diagnosis of toxocariasis is possible by immunoblotting.
- Instrumental techniques. In case of lung damage, oblakoid infiltrates, a “symptom of a blizzard,” are visualized on chest x-ray. Abdominal ultrasound with visceral form reveals hyperechoic rounded foci in parenchymal organs. Brain MRI is indicated in cases of suspected invasion of toxocars into the brain: rounded granulomas located in the cortex or subcortical are considered specific symptoms. If there are signs of heart damage, electrocardiography is performed; if there are any seizures, an EEG is prescribed.
Differential diagnosis is carried out with ascariasis, in which intestinal obstruction, acute obstructive respiratory failure are often observed. It is necessary to exclude opisthorchiasis and strongyloidosis, which occur with jaundice, pain in the right hypochondrium and stool breakdowns. The ocular form of toxocariasis is differentiated from retinoblastoma, manifested by leukocoria, strabismus, lacrimation, photophobia, secondary glaucoma. Skin manifestations may be the result of insect bites, exposure to allergens.
Treatment
Indications for inpatient treatment are visceral forms of the disease. Bed rest is prescribed only in the presence of fever and it is recommended up to 2-4 days of sustained absence of high body temperature figures. There is no special diet, however, given some side effects of the drugs used, it is recommended to refrain from taking fatty, fried foods, alcohol, spices, marinades, sweets. It is important to observe the drinking regime, to exclude contact with possible food and household allergens. Unauthorized termination of the initiated medical treatment is unacceptable.
Anthelmintic therapy. Albendazole, mebendazole, diethylcarbamazine, which are used in tablet forms, are considered highly effective anthelmintic agents for the destruction of migrating larvae. With respect to toxocars located in granulomas, these drugs do not have a pronounced neutralizing effect.
Surgical methods of treatment are used for ocular toxocariasis and include microsurgical removal of granulomas, laser coagulation for splitting larvae in the eye media and correction of retinal detachment.
Symptomatic therapy is carried out according to indications. It includes antipyretics (paracetamol, celecoxib), detoxification (chlosol, glucose-salt solutions), desensitizing (gluconate, calcium chloride), antihistamines (chlorapyramine, desloratadine), expectorants (acetylcysteine, mucaltin), enzymatic (pancreatin) and other agents.
Prognosis and prevention
The prognosis for uncomplicated forms is favorable, no fatal cases are described. The duration of taking medications can be up to 3-4 weeks or more, sometimes several courses are required with breaks of 2-4 months. The criteria for effectiveness are considered to be the disappearance of the clinic, a decrease in the level of antibodies and eosinophilia of the blood. Cases of disseminated toxocariasis among HIV-infected persons in the AIDS stage, as well as patients taking systemic glucocorticosteroids for a long time or undergoing radiation therapy for oncological diseases are described.
Preventive vaccines based on DNA have shown a positive effect in experiments on mice, research is currently ongoing. It is recommended to monitor the population of stray animals, to conduct dog walking in specially designated areas. Important measures of nonspecific control of morbidity are weaning children from eating the earth, instilling personal hygiene skills after playing outside, in the sandbox, communicating with animals; thorough washing of berries, greens, vegetables and fruits before eating; prescribing anthelmintic drugs to pregnant dogs, newborn puppies.