Parasites and Health [Last Modified: ]
[Toxocara canis] [Toxocara cati] [Toxocara leonina]
Causal Agent Life Cycle Geographic Distribution Clinical Features Laboratory Diagnosis Treatment

Clinical Features:
Many human infections are asymptomatic, with only eosinophilia and positive serology.  The two main clinical presentations of toxocariasis are visceral larva migrans (VLM) and ocular larva migrans (OLM).  In VLM, which occurs mostly in preschool children, the larvae invade multiple tissues (liver, heart, lungs, brain, muscle) and cause various symptoms including fever, anorexia, weight loss, cough, wheezing, rashes, hepatosplenomegaly, and hypereosinophilia.  Death can occur rarely, by severe cardiac, pulmonary or neurologic involvement.  In OLM, the larvae produce various ophthalmologic lesions, which in some cases have been misdiagnosed as retinoblastoma, resulting in surgical enucleation.  OLM often occurs in older children or young adults, with only rare eosinophilia or visceral manifestations.

Laboratory Diagnosis:
In this parasitic disease the diagnosis does not rest on identification of the parasite.  Since the larvae do not develop into adults in humans, a stool examination would not detect any Toxocara eggs.  However, the presence of Ascaris and Trichuris eggs in feces, indicating fecal exposure, increases the probability of Toxocara in the tissues.

For both VLM and OLM, a presumptive diagnosis rests on clinical signs, history of exposure to puppies, laboratory findings (including eosinophilia), and the detection of antibodies to Toxocara.

Diagnostic findings

VLM is treated with antiparasitic drugs, usually in combination with antiinflammatory medications.  The antiparasitic drug recommended in The Medical Letter is albendazole*, with mebendazole* as an alternative.  For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).

* This drug is approved by the FDA, but considered investigational for this purpose.


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