Molecular studies of the acute infection, latency and reactivation of equine herpesvirus-1 (EHV-1) in the mouse model

The murine intranasal (i.n.) infection model was used to study the molecular distribution of equine herpesvirus-1 (EHV-1) during acute infection, latency and following a reactivation stimulus. After inoculation, infectious virus was detected in lungs, nasal turbinates, brains and olfactory bulbs during the acute phase. A nested PCR (nPCR) readily detected virus in these tissues and, in addition, virus was detected in spleens and (in the second round of nPCR) in peripheral blood mononuclear cells (PBMC). A digoxigenin-labelled in situ hybridization probe detected EHV-1 DNA in bronchiolar and vascular endothelium in the lungs and in and around germinal centres in the spleens. One month later, although infectious virus was absent from all tissues, the trigeminal ganglia, olfactory bulb and PBMC remained positive for virus DNA although this was detected only on the second round of nPCR. Furthermore, in situ hybridization, using either DNA or RNA probes, suggested that little or no transcription of virus occurred in neural tissues during the ‘latent phase’. Following a reactivation stimulus, infectious virus was not isolated from any tissues, however, EHV-1 DNA was detected on the first round of nPCR in olfactory bulb, trigeminal ganglia and PBMC. This suggested a quantitative increase in EHV-1 DNA occurred following reactivation stimulus. The significance of these results is discussed in relation to the molecular state of EHV-1 in different tissues at various stages of infection and the validity of the murine model for studying latency and reactivation of EHV-1 in the horses.