Nematodes of the genus Toxocara belong to the Ascarididae. Toxocara canis and T. cati are parasites which can cause a visceral larva migrans syndrome (fever, hepatitis, pneumonitis, urticarial, eosinophilia) with or without asthma. If they reach the retina, they may lead to chorioretinitis with blindness as a possible outcome. Infection occurs by swallowing an egg that has reached the outside world via the feces of a dog (T. canis) or a cat (T. cati). A Toxocara parasite may become adult and eggs may appear in the faeces of humans in exceptional circumstances (e.g. HIV infection AIDS). Definitive diagnosis is established via detection of larvae in a tissue biopsy, though symptoms rarely justify such an aggressive diagnostic approach. ELISA is useful for visceral larva migrans, but not for ocular larva migrans. Cross-reactivity with other parasite antigens is common. Treatment is based on steroids and albendazole or diethylcarbamazepine (DEC). Nevertheless the effect of the anthelmintic treatment on the extra-intestinal larvae is limited. Intra-ocular infection resulting from Toxocara larvae may lead to traction upon the retina resulting in retinal detachment. Vitreoretinal surgery has a good chance of leading to an improvement in vision in approximately 50% of cases.
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