Detection of Bovine Herpesvirus Type 1 in Blood from Naturally Infected Cattle by Using a Sensitive PCR That Discriminates between Wild-Type Virus and Virus Lacking Glycoprotein E

In the present study, we report for the first time on the detection of bovine herpesvirus type 1 (BHV-1) in whole-blood samples derived from naturally infected cattle. Sensitive PCR assays specific for glycoprotein B (gB), gC, and gE of BHV-1 allow the detection of one BHV-1 DNA copy in 10(5) to 10(7) peripheral blood leukocytes (PBLs). The incidence of BHV-1-positive PBLs in naturally infected cattle appears to be quite high (92.2% positive PBLs among all samples tested), although in most cases only between 10(-5) and 10(-7) positive leukocytes were present. The results demonstrate that the viral DNA is detectable not only in the peripheral blood of acutely infected animals but, more importantly, also in the peripheral blood of subclinically infected cattle. The gE-specific PCR described in the report allows discrimination between wild-type (WT) virus-infected and vaccinated animals, which is of importance for control programs that use the recently introduced vaccination strategy with a gE-negative virus. The results further show that doubtful serological results can be verified or falsified and that individual animals can be monitored for the presence or absence of WT BHV-1 or gE-negative virus in cattle herds. The PCR protocols allow the detection of BHV-1 prior to seroconversion or in BHV-1-seronegative cattle. Finally, the results indicate the simultaneous presence of WT and gE-negative vaccine virus in the PBLs of several cattle. Therefore, investigations of viremia in naturally and experimentally infected cattle and on the identification of infected cell types of bovine PBLs can be now performed.