Investigations on bovine herpesvirus 4 infections in cattle in Bulgaria

Cattle infected with BHV 4 show respiratory symptoms, gastrointestinal and postnatal genital disorders. The virus is a cofactor of bacterial infections. This paper reflects data on the prevalence of BHV 4 infections in several herds, among breeding animals and bulls from artificial insemination stations (AIS). One hundred and twenty six serum samples from bulls were investigated by MVNT and 45 (35.7%) were positive. Epizootiological and clinical studies on the prevalence of BHV 4 infections were limited to bovine farms with suspected infection with this virus. To establish seroconversion to the virus, double serum samples from 264 cattle – 165 native-born cows and 99 imported pregnant heifers were investigated by the microvirus neutralisation test (MVNT) and commercial ELISA for the detection of antibodies against BHV 4. Ninety-nine samples (37.5%) were positive in the MVNT and 110 samples (41.6%) – in ELISA. One out of the seven milk samples from cows with signs of mammary glands involvement was positive in the polymerase chain reaction (PCR) performed to detect the gB and Tk virus genes. Four of the ten whole blood samples from acutely ill animals were positive for BHV 4 DNA by PCR. The results of the present study confirmed that the BHV 4 circulated within the Bulgarian cattle population.