Toxocaridae

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Toxocaridae

A canine roundworm (Toxocara canis) egg. Photo taken through a microscope at 400x.

Kingdom:	Animalia
Phylum:	Nematoda
Class:	Secernentea
Order:	Ascaridida
Family:	Toxocaridae

Toxocaridae is a family of parasitic nematodes that infect canids and felids and which can cause visceral larva migrans in humans. In humans, the worms cannot reproduce.

Three important species include:

Toxocara canis, which infects dogs,
Toxocara cati, which infects cats and which lacks intermediate hosts,
Toxocara vitulorum, which infects buffalo and cattle.

[edit] Infection

Infection by T. canis or T. cati can cause various clinical manifestations. One of these is visceral larva migrans, wherein the larvae are unable to develop in humans as they do in cats and dogs, their natural hosts. Arrested development leaves the larvae to wander aimlessly in the body, causing inflammation, most commonly in the liver and lungs.

Eggs are introduced into the body through ingestion. This can occur when eggs are deposited on the hands or face, after handling infected dogs or cats. In children without exposure to animals, eggs can be introduced by directly ingesting egg-contaminated soil while playing in a yard or on a playground. Usually, the scenario involves a young child with a new puppy. Unfortunately, many young children who have been infected with these larvae, which form granulomas in the eye, have been misdiagnosed to have retinoblastoma and have had their eyes erroneously removed.

[edit] Diagnosis

Direct identification of larvae in human disease is not feasible, so the diagnosis relies on history supported by serologic ELISA assay. The most sensitive assay, called E/S (excretory/secretory), contains 96 immunogenic antigens isolated from cultured T. canis larvae.