Periodic reappearance of bovine herpesvirus type 4 DNA in the sera of naturally and experimentally infected rabbits and calves.

A BHV-4 specific nested PCR was used for the detection of viral DNA in serum samples of rabbits and calves. All animals were followed up for 62 days, blood samples were taken for PCR studies every second day. Maternal infection of calves resulted in the repeated regular reappearance (10-14 days) of the virus (DNA) in serum samples. When PCR positive five-day-old calves were infected with tissue culture adapted virus, the reappearance of the DNA in the serum was shown to be irregular, nevertheless, DNA peaks reappeared during the whole observation period. A PCR negative calf infected at the age of 60 days was found to possess viraemia until p.i.d. 32. In rabbits treated intravenously with BHV-4 the inoculum or a primary viraemia was detected at p.i.d. 2-3 and p.i.d. 14-16. Published data on human herpesviruses suggest, that the target cells might be a pluripotent stem cell population of the bone marrow and differentiated virus-infected cells destroyed by the immune system might be the source of viral DNA detected in the serum. Frequency of DNA reappearance was depended on the age of the infected animals but not on the inoculated amount of BHV-4. The described phenomenon might be part of BHV-4 infection of very young animals.