Seroprevalence of Neospora caninum infection following an abortion outbreak in a dairy cattle herd

Objective To investigate the seroprevalence of Neospora caninum infection in a commercial dairy cattle herd, 15 months after detection of an abortion outbreak. Procedure Sera from the whole herd (0=266) were examined for N caninum antibodies by indirect fluorescent antibody test (IFAT) and immunoblot analysis. Herd records were reviewed to collate serological results with abortion history, proximity to carving, and pedigree data. Results The seroprevalence of N caninum infection was 24% (63/266) for IFAT titre greater than or equal to 160, 29% (78/266) for immunoblot positive (+ve), and 31% (82/266) for IFAT greater than or equal to 160 and/or immunoblot +ve; 94% (59/63) of animals with IFAT greater than or equal to 160 were immunoblot +ve. The association between seropositivity (IFAT greater than or equal to 160 and/or immunoblot +ve) and history of abortion was highly significant (P < 0.001); the seroprevalence was 86% (18/21) in aborting cows, compared with 30% (50/164) in non-aborting animals. The abortion rate for seropositive cows was 26% (18/68) compared with 3% (3/117) for seronegative animals. IFAT titres of infected cows were higher within 2 months of calving than at other times (P < 0.001). The association between seropositivity in dams and daughters was highly significant (P = 0.009). Conclusions The abortions were associated with N caninum infection and there was evidence of reactivation of latent infection close to calving and congenital transmission of infection. Immunodominant antigens identified by immunoblots may prove useful for improved diagnostic tests.