Equine herpes virus are DNA virus with linear doublestrand and belong to Herpesviridae family. The two most common types major importance are Equine herpes virus type 1 (EHV-1), which causes abortion, respiratory disease and neurologic disease; and Equine herpes virus type 4 (EHV4), which causes only respiratory disease but also occasionally causes abortion. EHV-1 and EHV-4 are the members of varicello virus genus in Alpha herpes virinae subfamily and are endemic in equine populations worldwide (Reed and Toribio, 2004; Fortier et al., 2010; MacLachlan and Dubovi, 2011). These viruses have 145 to 150 kb genomic DNA and glycoproteins that are important for cell attachment, entry and cell-to-cell spreading and induction of immune responses (Reed and Toribio, 2004; Azab et al., 2010). The common characteristics between all herpes virus infections are latency and persistent infection with periodic or continuous shedding (Sellon, 2007; Ataseven et al., 2009; MacLachlan and Dubovi, 2011) EHV-1 and EHV-4 can establish latent infections in trigeminal ganglia and T-lymphocytes. Latently infected animals are the major reservoirs of disease and frequent shedding of the virus from these asymptomatic carriers cause spread of virus to susceptible population (Slater et al., 1994; Chesters et al., 1997; Pusterla et al., 2009; Fortier et al., 2010) Epidemiological studies, suggest that the infection occurs during the few early weeks or months after birth occurs, generally before or after weaning, from adult mares that asymptomatically shed virus (Nicola Pusterla et al., 2005; Sellon, 2007). Techniques that are used for the diagnosis of EHV infection include: virus isolation as “gold standard”, serological tests and nucleic acid detection techniques (PCR). Several PCRbased methods have been developed for detection and identification of EHV-1 and EHV-4 DNA in aborted foetuses or nasal swabs (Sellon, 2007). qPCR technology offers a flexible and rapid method as compared to virus isolation. This is sensitive, specific and quantitative method which provides a very useful diagnostic ool for infectious diseases studies, so also a valuable aid for screening large numbers of samples (Diallo et al., 2006; Perkins et al., 2008; Dzieciatkowski et al., 2009; Hoffmann et al., 2009). The main target of this study is to survey circulation of virus and possible source of infection in equine population in North-East district of Iran that has the highest equine population with high prevalence of EHV-4.

Keywords