Repeated patent infection of adult dogs with Toxocara canis.

Three adult male greyhounds have been repeatedly infected with Toxocara canis by oral administration of 100 to 200 infective ova. Each infection has become patent as shown by the presence of eggs in faeces. Anthelmintic treatment between 7 and 14 weeks after infection yielded an average of 25% of the inoculum as adult worms. These dogs have continued to be fully susceptible to infection despite repeated exposure to this parasite, and despite the presence of serum antibody to both parasite surface and secreted antigens. These findings imply that adult dogs may not always be immune to toxocaral infection and may therefore contribute significantly to the problem of environmental contamination with T. canis ova.