Toxocara spp. are parasitic nematodes belonging to the order Ascaridida. In 1782, Toxocara canis was described as Ascaris canis and the clinical illness named visceral larval migrans (VLM) was ascribed in 1947 (Perlingiero and Gyorgy 1947) to Ascaris lumbricoides. However, Beaver et al. (1952) described a series of children who had eosinophilia and suffered severe multisystem diseases, and by serial sections of a larva from a patient, they identified the larva as T. canis. At about the same time, Wilder (1950) discovered lesions of the eyes containing nematode larvae, now known as ocular larva migrans (OLM). It was several years later before the larvae were identified as Toxocara (Nichols 1956). During the same period, studies were initiated and directed at serological diagnosis of VLM and demonstrated the use of indirect haemagglutination (Jung and Pacheco 1958). Most of the early attempts at serodiagnosis were disappointing, partly due to the use of antigens from adult stage worms because we now know that most of the larval antigens are not shared with the adult worms (Glickman et al. 1986). The breakthrough for serodiagnosis was the report of de Savigny (1975) describing the production of ES antigens by prolonged in vitro culture of T. canis larvae in serum-free medium, followed by the development of a diagnostic test (de Savigny et al. 1979).

Three different kinds of syndromes are associated with T. canis infection; visceral and ocular toxocarosis and the third, covert toxocarosis, which is a milder form of the syndrome VLM (Glickman et al. 1987; Taylor et al. 1987; Nathwani et al. 1992). However, most people do not develop any clinical symptoms after infection (Bass et al. 1983).

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VLM and OLM are in general associated with T. canis, but other ascarids can also cause some form of larva migrans, such as T. cati (definite host: cats), Baylisascaris procyonis (definite host: racoons), and Toxascaris (definite host: dogs and cats).

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