Neospora caninum and bovine virus diarrhoea virus infections in Swedish dairy cows in relation to abortion

The protozoan parasite Neospora caninum and bovine virus diarrhoea virus (B VDV) are recognized as important causes of bovine abortion and congenital d isease worldwide. In this study, serological investigations were performed to estimate the prevalence of N. caninum infection in Swedish dairy cattle, to assess to what extent it may affect abortion rates, and to determine po ssible effects of coinfection with BVDV. The overall N. caninum seroprevale nce in Swedish dairy cows was estimated at 2% (16/780), and the BVDV seropr evalence was 32% (249/780). Among aborting cows from herds with abortion pr oblems, 7% (26/378) had antibodies to N. caninum and 42% (153/378) to BVDV. Seventeen of the N. caninum positive animals also had antibodies to BVDV. There was a statistically significant (P = 0.013) association between prese nce of antibodies to N. caninum and BVDV. In a case-control study comprisin g sera from cows in herds without recognized abortion problems, 6% (5/89) a nd 1% (1/89) of sera from aborting and non-aborting cows, respectively, had antibodies to N. caninum. Two of the N. caninum seropositive aborting cows also had antibodies to BVDV. These results confirm that N. caninum infecti on is associated with bovine abortion in Sweden and also indicate that ther e might be concurrent effects of N. caninum and BVDV. It is concluded that Swedish dairy cows have a low prevalence of N. caninum infection which is f avourable in relation to possible future control programmes. (C) 2000 Harco urt Publishers Ltd.