Viral and Host Strategies for Regulation of Latency and Reactivation in Equid Herpesviruses

Nine members of the family Herpesviridae infect equines and two of them (EHV1 and EHV4) are the globally significant pathogens causing respiratory disease, abortion and more rarely paralysis. The ability of equid herpesviruses to establish life-long latent infection in lymphoid and neural tissues with periodic reactivation and shedding is central to the maintenance of these viruses in horse populations. Over 50% of horses become latently infected after infection with EHV1 and EHV4. During latency, expression of viral genes is highly restricted with expression of few or no viral proteins. The recent scientific advances have provided insight into the mechanism of equine herpesvirus pathogenesis, including latency. The establishment of latent infection is highly coordinated process regulated by inter-play of viral, host and environmental factors. In this article, we review how molecular, cellular and viral regulatory mechanisms influence the switch between latent and lytic infections.