Neospora caninum infection in stray and farm dogs: seroepidemiological study and oocyst shedding.

In a previous study, farm and stray dogs were considered potential high risk populations of Neospora caninum infection in Spain. Consequently, we decided to investigate the significance of N. caninum infection in these populations. Specific antibodies were detected in 120 out of 275 dog sera (43.6%), with titres ranging from 1:50 to 1:800. Differences in seroprevalence between farm (47.5%, 67/141) and stray (39.5%, 53/134) dogs were not significant (P>0.05; χ(2) test), but farm dogs showed significantly higher titres (P<0.01; Student's t-test). N. caninum seroprevalence in farm dogs was associated with increasing age (P<0.01; χ(2) test) and dogs with free access to the farm were more likely to be seropositive than controlled-dogs (P<0.05; χ(2) test). The presence of anti-N. caninum antibodies was more often detected in dogs from farms with 5-20% N. caninum within-herd seroprevalence (56.9%, 37/65) than those from farms with 0-5% seroprevalence (38%, 23/60) (P<0.05; χ(2) test). We microscopically observed N. caninum-like oocysts in the faeces from one farm dog, but the number of oocysts was very low, and the aetiology could not be confirmed. Also, parasite isolation was attempted from fresh neural tissue from stray dogs but was unsuccessful.