Low exposure of urban dogs in metropolitan Sydney, Australia to Toxocara canis demonstrated by ELISA using T. canis excretory-secretory (E/S) larval antigens.

Canine roundworm, Toxocara canis, is considered ubiquitous but patent infections are rare in adult owned urban dogs. Hepato-pulmonary migration of T. canis is common in young dogs, but in adult dogs, the migration of T. canis is arrested in tissues and larvae are inhibited. During this somatic migration, T. canis release excretory-secretory (E/S) larval antigens against which the host mounts an immune response. Detection of anti-T. canis E/S immunoglobulins is considered a proxy for the presence of arrested somatic T. canis larvae. By screening several cohorts of dogs in New South Wales (NSW), Australia, we determined the seroprevalence of anti-T. canis E/S in urban owned dogs visiting a veterinary teaching hospital in Sydney to be 3.8 % (n = 53), which was significantly lower (two-proportion z-test, P < 0.05) than the seroprevalence in pet dogs in regional western NSW (22.2 %, n = 63), and rehomed greyhounds (53.6 %, n = 28). Using a logistic regression model, the risk of testing positive in regional pet dogs (odds ratio [OR] = 37.0) and rehomed greyhounds (OR = 81.0) was significantly higher than in urban dogs (P < 0.05). Although routine deworming of dogs eliminates patent infection, our data show a low number of urban dogs with anti-T. canis E/S antibodies, which implies that the majority of these dogs were not exposed to T. canis previously, do not possess inhibited T. canis larvae, and in the case of intact females, will not transmit it to their puppies.