Herd-based diagnosis of Neospora caninum-induced endemic and epidemic abortion in cows and evidence for congenital and postnatal transmission

Aborting and nonaborting cows and their dams or daughters were studied to determine if herd abortion problems were associated with the presence of Neospora caninum antibodies and to estimate when aborting cows may have acquired the infection. Cows were sampled from 20 herds that had experienced an abortion epidemic presumed to have been caused by N. caninum and from 2 herds experiencing endemic abortion. Seroprevalence for 14 herds experiencing an epidemic ranged from 7% to 70%, as estimated by enzyme-linked immunosorbent assay. A strong association between seropositivity and abortion was found for only 5 of 14 herds with a presumed diagnosis of N. caninum abortion (P less than or equal to 0.015, lower 95% confidence interval of odds ratio greater than or equal to 1.2), indicating N. caninum may be overdiagnosed as the cause of an abortion epidemic in some herds. No association was found between dam and daughter seropositivity for herds experiencing an epidemic (P greater than or equal to 0.17), suggesting that most cows aborting during an epidemic were infected postnatally. For the 2 herds with endemic abortion (A, B), odds of an aborting cow having N. caninum antibodies were 3.4-fold (herd A) and 7.0-fold (herd B) higher than odds for nonaborting cows (P less than or equal to 0.05). Cows that aborted a fetus infected with N. caninum were more likely to have had a previous seropositive daughter than were nonaborting seronegative cows (P less than or equal to 0.0025), suggesting that infection had been acquired before conception of the aborted fetus.