A sensitive and specific PCR/Southern blot assay for detection of bovine herpesvirus 4 in calves infected experimentally.
A polymerase chain reaction (PCR)/Southern blot assay for detection of bovine herpesvirus 4 (BHV-4) in the background of bovine cellular DNA was developed. A BHV-4 specific sequence within the gene coding for the glycoprotein B (gB) was selected for primer sequences to guarantee the specificity of the assay. With a detection limit of 6 molecules BHV-4 DNA in the background of 1 µg of cellular DNA (approx. 150 000 bovine cells) this PCR/Southern blot assay represents a highly sensitive method for detection of BHV-4 DNA. At low concentrations of BHV-4 genomes, this assay also allowed the estimation of the copy number of BHV-4: a distinction between <6, 6-59 and >60 BHV-4 genomes/100 µl DNA suspension was possible. Tissue and blood samples of 2 calves, infected experimentally with BHV-4 were examined for the prevalence of BHV-4 DNA 130 days after infection. 10 days before taking samples, one of the calves was immunosuppressed with dexamethasone. In both calves, BHV-4 DNA was detected in the leukocyte fraction of the blood, and beyond that in lower quantities in the spleen and the kidney of the immunosuppressed calf. It is assumed that a latent BHV-4 infection was activated after application of dexamethasone and that the leukocyte fraction of the blood represents one site of latency of BHV-4 in cattle.