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Toxocariasis

Toxocariasis is a parasitic infection with the dog or cat roundworm, Toxocara canis or Toxocara cati, respectively. Ingestion of these worms causes the condition, visceral larval migrans. more...

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Epidemiology

Toxocariasis is a worldwide infection. Epidemiologic surveys show a 2-5% positive rate in healthy adults from urban Western countries and 14.2-37% in rural areas. In tropical countries, surveys show a positive rate of 63.2% in Bali, 86% in Saint Lucia, and 92.8% in Réunion. Toxocariasis is most commonly a disease of children, typically children aged 2-7 years.

Pathophysiology

Adult worms of the Toxocara species live in the small intestine of dogs and cats. They range from 4-12 cm in length. Almost all puppies are infected at or soon after birth. During the summer, Toxocara eggs are shed and become infective. They survive for years in the environment, and humans typically ingest the eggs by oral contact with contaminated hands. Once introduced into the human intestine, the eggs hatch, releasing the larvae. The larval form is less than 0.5 mm in length and 0.02 mm wide. The larvae penetrate the bowel wall and migrate through vessels to the muscles, liver, and lung and sometimes to the eye and brain as well.

Disease severity depends not only on the number of larvae ingested but also on the degree of allergic reaction. The inflammatory reaction causes epithelial cells to surround each larva, and, subsequently, a dense fibrous capsule invests each granuloma.

Features

Weakness
Pruritus
Rash
Difficulty breathing
Abdominal pain
Eosinophilia
Increased total serum immunoglobulin E (IgE) level
Elevated antibody titers to T canis

Diagnosis

In suspected cases, diagnosis is confirmed by an increase in the anti-Toxocara excretory-secretory antigen IgE level

Treatment

Mebendazole or thiobendazole are the treatments of choice.

Prognosis

Toxocariasis is almost always a benign, asymptomatic, and self-limiting disease, although brain involvement can cause brain damage, meningitis, encephalitis, or epilepsy. Ocular involvement may cause loss of visual acuity or unilateral blindness. Pulmonary and hepatic forms can cause protracted symptoms if the patient does not receive treatment.

Prevention

The eggs of Toxocara species are widespread in parks, playgrounds, yards, and in homes and apartments where the occupants have dogs or cats. Elimination of eggs from the environment is not possible; therefore, prevention depends on proper hygiene, including handwashing after contact with pets. Public policies that have attempted to eradicate Toxocara infection in dogs and cats have had limited success.

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HUMAN TOXOCARIASIS: HUMORAL RESPONSE (IgG, IgA AND IgE) ANTI-Toxocara canis AND CLINICAL-LABORATORIAL CORRELATION IN PATIENTS FOLLOWING CHEMOTHERAPY
From Revista do Instituto de Medicina Tropical de Sao Paulo, 3/1/04 by Rubinsky-Elephant, Guita

A serological follow-up was carried out in 27 children with loxocariasis (23 with visceral, 3 with both visceral and ocular manifestations and I with ocular loxocariasis, a total of 159 samples), treated with thiabendazole. The ages of the children varied from 1 to 12 years (average of 4.2 years), and the follow up treatment varied from 22 to 1 16 months (average of 65 months). The enzyme linked immunosorbcnt assay (ELISA) and Western blotting technique for the detection of specific IgG, IgA and IgR anti-Tb.wcam were standardized, using excretory-secretory antigen obtained from Toxocara canis second stage larvae culture. The avidity of specific antibodies IgG was also evaluated in both tests.

The sensitivity of KLISA IgG, IgA and IgR were 100%, 47.8% and 78.3% respectively, in visceral toxocariais patients. The humoral immune response was stronger in these patients compared to those with ocular manifestations. Although 84% of the patients presented one or more parasites in fcccs, the number of parasites did not affect the specific humoral response. In the follow-up after treatment, the first isotype that showed significant differences in titcrs was IgE antibodies, in the first year. Specific IgA showed differences in the second year and specific IgG, in the fourth year after treatment. Although the decrease of IgG titcrs was observed, the levels still remained elevated for many years. all patients presented high avidity IgG antibodies, in both ELISA and WB tests, pointing to a chronic phase of the disease.

The WB technique was performed with gradient polyacrilamidc gel (5-15%), showing a pattern of bands ranging from 29 to >205 kDa, with the predominance of the 29-38 and 48-54 kDa bands. WB-IgG showed the highest sensitivity (100%), followed by IgB (91.3%) and IgA (73.9%). The WB profile could be divided in two groups: a constant pattern of bands throughout the follow-up study and another that presented a decrease in reactivity to some bands. A decrease statistically significant was seen in the pattern of WB-IgG reactivity to bands >205 kDa in the third year and in WB-IgA to bands 81-93, 66, 48-54 and 29-38 kDa, in the first year after treatment.

The evaluation of laboratorial data showed a decrease statistically significant in the number of leukocytes, titers of isohaemagglutinins anti-A and absolute number of cosinophils, in patients with visceral toxocariasis, one year after treatment. In patients with ocular manifestation, the number of leukocytes and eosinophils were normal. At the beginning of the study, hypergammaglobulinemia was observed as well high levels of antibodies IgE and IgM. There was a correlation between the liters of specific IgK and the number of eosinophils, as well as correlation between total and specific IgG.

* This thesis is available at the Library of the Instituto de Medicina Tropical dc Sao Paulo

Guita RUBINSKY-ELEPHANT

Lab. Soroepidemiologia e Imunobiologia

Instiluto de Medicina Tropical de S. Paulo

guitare@usp.br

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