Equine herpesvirus-4 kinetics in peripheral blood leukocytes and nasopharyngeal secretions in foals using quantitative real-time TaqMan PCR

Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis 95616, USA.

Based on the hypothesis that the viral load of cells infected with EHV-4 will likely change during the course of disease, TaqMan PCR was used to investigate and characterize the kinetics of EHV-4 viral DNA load (glycoprotein B gene) and transcriptional activity (glycoprotein B and latency-associated transcripts) in peripheral blood leukocytes (PBLs) and nasopharyngeal secretions (NSs) collected from 11 foals during a field outbreak of respiratory disease. The EHV-4 DNA load in PBLs was low and of short duration after onset of clinical signs. In contrast, the EHV-4 load in NSs remained high for the majority of the foals over a period of 4 weeks. Viral replication determined by detection of mRNA expression of the structural glycoprotein B was detected only in NSs during the first 7 days after onset of clinical signs for most foals. The majority of foals expressed latency-associated transcripts in NS sonly during the first 7 days after onset of clinical signs. Persistence of the expression of latency-associated transcripts in NS, as a reflection of a latent viral state, was not documented during the 28-day study period. Based on these results, it was concluded that lytic infection with EHV-4 can be diagnosed either by high EHV-4 DNA load of glycoprotein B gene or by detection of transcriptional activity of glycoprotein B.

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