Neospora caninum and bovine viral diarrhoea virus infections in dairy cattle : investigation of seroprevalences in imported and localcrossbreed cows in dairy herds from southern Vietnam

Abstract: The protozoan parasite Neospora caninum and bovine viral diarrhoea virus (BVDV) are major causes of abortion in cattle and related with economic losses inmany countries. When introduced into a herd, both infections can be expected to remain for a long time if no control measures are taken. The purpose of this studywas to investigate the prevalences of N. caninum and BVDV infections in dairy cows in South Vietnam. Specific goals were to study the seroprevalences of the infections in dairy cows from state herds and smallholder farms, and if there were differences in seroprevalences between imported Holstein Friesian cows and local crossbreeds.A total of 345 serum samples, including 215 sera collected from 5 state farms and 130 sera from 97 smallholder herds, from southern Vietnam were analysed for presence of antibodies to N. caninum and BVDV. In state herds with imported cows, the N. caninum and BVDV seroprevalences varied between 38-53% and 78-93%, respectively. The infection rates were higher in imported cows than in localcrossbreeds. The results suggested that horizontal transmission of N. caninum was occurring in at least 4 of the 5 herds. Among cows from smallholder herds withonly local crossbreeds, the prevalences of N. caninum and BVDV were 19% and 18%, respectively. BVDV antigen was not found in any cow. This is the first report on BVDV infection in Vietnam.It was concluded that N. caninum and BVDV infections are present and appear to be widespread in dairy cows in south Vietnam. Given the high prevalence among imported cows found in this study, it seems advisable that only cattle that are pretested free from N. caninum infection are imported into the country. Further, it is important not to import any persistently infected BVDV cattle or antibody positive cows that may carry infected foetuses.