Evaluation of a commercial E(rns)-capture ELISA for detection of BVDV in routine diagnostic cattle serum samples

BACKGROUND: Bovine viral diarrhoea virus (BVDV) is an important pathogen in cattle. The ability of the virus to cross the placenta during early pregnancy can result in the birth of persistently infected (PI) calves. These calves shed the virus during their entire lifespan and are the key transmitters of infection. Consequently, identification (and subsequent removal) of PI animals is necessary to rapidly clear infected herds from the virus. The objective of this study was to evaluate the suitability of a commercial E(rns)-capture ELISA, in comparison to the indirect immunoperoxidase test (IPX), for routine diagnostic detection of BVDV within a control programme. In addition, the effect of passive immunity and heat-inactivation of the samples on the performance of the ELISA was studied. METHODS: In the process of virus clearance within the Swedish BVDV control programme, all calves born in infected herds are tested for virus and antibodies. From such samples, sent in for routine diagnostics to SVA, we selected 220 sera collected from 32 beef herds and 29 dairy herds. All sera were tested for BVDV antigen using the E(rns )ELISA, and the results were compared to the results from the IPX used within the routine diagnostics. RESULTS: All 130 samples categorized as virus negative by IPX were tested negative in the ELISA, and all 90 samples categorized as virus positive were tested positive, i.e. the relative sensitivity and specificity of the ELISA was 100% in relation to IPX, and the agreement between the tests was perfect. CONCLUSION: We can conclude that the E(rns )ELISA is a valid alternative that has several advantages compared to IPX. Our results clearly demonstrate that it performs well under Swedish conditions, and that its performance is comparable with the IPX test. It is highly sensitive and specific, can be used for testing of heat-inactivated samples, precolostral testing, and probably to detect PI animals at an earlier age than the IPX

Epidemiology of bovine viral diarrhoea virus and bovine herpesvirus type1 infections in dairy cattle herds

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

Natural infection of cattle with an atypical `HoBi'-like pestivirus – Implications for BVD control and for the safety of biological products

During a study on Bovine Viral Diarrhoea (BVD) epidemiology in Thailand, a pestivirus was detected in serum from a calf. Comparative nucleotide sequence analysis showed that this virus was closely related to a recently described atypical pestivirus (D32/00_`HoBi') that was first isolated from a batch of foetal calf serum collected in Brazil. The results from virus neutralisation tests performed on sera collected from cattle in the herd of the infected calf, showed that these cattle had markedly higher antibody titres against the atypical pestivirus `HoBi' than against Bovine Viral Diarrhoea Virus types 1 and 2, or Border Disease Virus. The results also supported, consequently, the results from the molecular analysis, and demonstrated that a `HoBi'-like pestivirus had been introduced to, and was now circulating in the herd. This study is the first to report a natural infection in cattle with a virus related to this atypical pestivirus, and it suggests that this group of pestiviruses may already be spread in cattle populations. The findings have implications for BVD control and for the biosafety of vaccines and other biological products produced with foetal calf serum. Consequently, these atypical pestiviruses should be included in serological assays, and any diagnostic assay aimed at detection of pestiviruses in biological products or animals should be tested for its ability to detect them