Evaluation of an enzyme-linked immunosorbent assay for the serological diagnosis of Neospora caninum infection in sheep and determination of the apparent prevalence of infection in New Zealand

Neospora caninum has recently been shown to be a cause of abortions of sheep in New Zealand. A commercially available enzyme-linked immunosorbent assay (ELISA) was validated for use in sheep with sera from experimentally infected sheep. A cut-off threshold was established that demonstrated sero-conversion between 7 and 14 days post-infection. Higher inocula led to earlier sero-conversion. This ELISA was applied to 640 sera collected from rams across New Zealand and 0.625% (±0.61%) (4/640) were shown to be serologically positive. The four positive sera were also demonstrated to be positive by indirect fluorescent antibody test (IFAT). The ELISA evaluated here lends itself more readily to large-scale investigations than IFAT. The low background of N. caninum infection in the New Zealand sheep population suggests that N. caninum abortions could be more easily diagnosed by serological means than in populations with higher background sero-prevalence.