Specific IgG antibodies against Toxocara are used to determine exposure to Toxocara canis.
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Toxocariasis is an infection caused by ingesting Toxocara canis dog larvae or, more rarely, the Toxocara cati cat parasite. Park grounds are usually contaminated with Toxocara canis eggs, and the parasite can cause human disease by affecting the liver, heart, lungs, muscles, eyes, and brain.
There are generally 3 recognized Toxocara infection syndromes:
In children, asymptomatic toxocariasis is a mild, subclinical, febrile illness. Symptoms include coughing, difficulty sleeping, abdominal pain, headaches, and behavior problems. Clinical examination may reveal hepatomegaly, lymphadenitis, or even respiratory wheezing.
The visceral larva migrans are caused by the migration of the larvae through the human internal organs and the resulting inflammatory reaction. A variety of symptoms can occur, such as fatigue, anorexia, weight loss, pneumonia, fever, cough, bronchospasm, abdominal pain, headaches, rashes, and occasionally seizures. Clinical examination may reveal hepatomegaly, lymphadenitis, or even respiratory wheezing. Occasionally, pleural effusions are developed. Severe cases can lead to myocarditis or respiratory failure.
Ocular larva migrans, caused by the larva's migration to the posterior part of the eye, tend to occur in older children and young adults. Patients may have impaired vision, redness of the eye, or leukocoria (a white pupil appearance). Granulomas and choroidal retinitis are observed in the retina, especially in the macula. The disease can result in vision loss, retinal fibrosis, retinoblastoma, and retinal detachment.
The disease affects up to 5% of the population in developed countries, while in some tropical countries, the prevalence exceeds 40%.
Diagnosis of toxocariasis is difficult because confirmation of infection requires larval biopsy. Thus, using serological tests to detect the presence of Toxocara antibodies is the easiest way to detect the disease. Eosinophilia may occur, most often in patients with visceral migratory larvae. Fertilizer parasitics for ova and pests are not used since parasite eggs are only excreted by animals, not humans.
Currently, antibody screening is the only way to confirm the clinical diagnosis. The best serological test for Toxocara is ELISA, but it cannot distinguish between current and past parasitic infections.
See also: Toxocara canis, IgG Confirmatory Antibodies
