Equine Herpesvirus 1 and 4 Respiratory Disease in the Horse

Equine herpesvirus (EHV)-1 and -4 associated respiratory disease in the horse occurs worldwide. Clinically there are no distinguishing characteristics between EHV-1 and EHV-4 infection. Disease is spread between animals by aerosolized virus, direct contact with infected respiratory secretions, or fomites. Diagnosis can be made by virus isolation, PCR of nasopharyngeal secretions or peripheral blood mononuclear cells, or serology. The characteristics of the protective immune response against EHV-1/4 infection have not been well described, but it is likely a combination of humoral and cell-mediated immunity. Current vaccines stimulate primarily a humoral immune response, which may decrease the severity of clinical signs, viremia, and viral shedding, but does not provide protection from infection. Since suckling foals have recently been shown to be an important reservoir in the transmission of EHV-1 and EHV-4, they ought to be the target for immunoprophylaxis to eliminate or significantly reduce EHV infections in the field and prevent the establishment of a latent state. Until more effective vaccine strategies are developed, appropriate herd management is essential to preventing or containing outbreaks of EHV-1/4.