In order to study the role played by bovine herpesvirus 4 (BoHV-4) in bovinemastitis, PCR experiments were performed on a Hungarian dairy herd of 2000 cows. Although the BoHV-4 ORF50/Rta homolog, immediate early gene 2 (IE2), has been shown to activate several BoHV-4 early and late promoters in cotransfection assays, there is no direct proof of its indispensability for progression of the virus to the lytic replication cycle in the context of the viral genome. Viral DNA were amplified by a nested PCR assay from 54.8% of peripheral blood leukocyte samples of newborn calves taken before colostrum uptake, and from all cattle and from their colostrums. Two groups of prototype strains were originated from the first isolates: the DN599-type strains (American group) and the Movar-type strains (European group). This finding could be considered a new important step in studies on the potential pathogenesis related to BoHV-4. Sci. The identity of the isolates was confirmed by PCR assays targeting three ORFs of the viral genome.
These results demonstrate the usefulness of the rabbit as a model for studying the pathogenesis of BHV-4 infection in cattle. In 2 animals, the virus was recovered repeatedly during 1 year from peripheral blood leukocytes by cocultivation with bovine lung cells. We thus conclude that BHV4 is unlikely to be a major pathogen of cats. It is concluded that BoHV-4 IE2 is a key factor in determining the outcome of BoHV-4 infection.