Epsilon Open Archive

Abstract

Bovine viral diarrhoea virus (BVDV) and bovine herpesvirus type 1 (BHV-1) infections are endemic and cause disease in cattle populations worldwide. The losses due to the diseases are high in affected countries and must be regarded as a serious animal welfare problem. In Sweden BHV-1 has been eradicated and more than 98% of the herds are BVDV free. This long-term study was conducted to obtain knowledge of relevance for control of both these infections in dairy herds in Thailand. The epidemiological pattern of BVDV and BHV-1 infections was studied in 186 dairy herds by repeated bulk tank milk (BTM) analysis. A subset of 11 herds was selected for individual testing. The serum and BTM were tested for antibodies to the viruses using indirect ELISA tests. The results demonstrated a selfclearance process of both infections at the herd/regional level, without any control measures. There was an apparently lack of reactivation of BHV-1 infected animals. A significant association of BHV-1 and BVDV indicate that common risk factors are associated with seropositivity. Factors discussed were the serological status of imported cows and artificial insemination activities. A low incidence rate of BVDV was found among breeding cattle in 5 out of 11 herds. One herd, however, had a high seroconversion rate to BVDV and a viraemic calf was identified by an Erns capture ELISA. Genetic characterization showed that this calf was infected with a virus closely related to a recently described atypical pestivirus (HoBi) detected in a foetal calf serum from Brazil. Comparative neutralisation tests suggest that seroconversions in this herd were caused by the ‘HoBi-like’ virus and that it has been recently introduced to the region. Further studies must be performed to elucidate how this virus has been introduced to the cattle population in Thailand and it might have been spread to cattle all over the world. However, this study shows that the self clearance process in Thai dairy herds of both BVDV and BHV-1 infections will probably continue if there is awareness of biosecurity. Imported animals and biological products should be secured free from both BVDV and BHV-1.