Equine Herpesvirus 1

Equine herpesvirus 1 (EHV-1) is a virus of the family Herpesviridae that causes abortion, respiratory disease and occasionally neonatal mortality in horses. Initial spread of EHV-1 by a newly introduced horse through direct and indirect contact can lead to abortion and perinatal infection in up to 70 percent of a previously unexposed herd. Abortion usually occurs in the last four months of gestation, two to four weeks after infection of the mare. Perinatal (around the time of birth) infection can lead to pneumonia and death. Encephalitis can occur in affected animals, leading to ataxia, paralysis, and death. There is a vaccine available (ATCvet code QI05AA11), however its efficacy is questionable.

The virus cross-reacts with Equine herpesvirus 4 in many serological laboratory tests. Commercial diagnostic tests are available to distinguish the two viruses using monoclontal antibody based reagents. The virus is easily isolated in cell culture and can be readily detected during acute infection using molecular diagnostic methods such as polymerase chain reaction (PCR).

Recent molecular epidemiology studies have identified a single nucleotide polymorphism (SNP) which varies between EHV-1 field isolates and shows a highly statistically significant correlation with paralytic compared with non-paralytic disease outbreaks. The SNP corresponds to a single amino acid change in the DNA polymerase enzyme, which is an essential enzyme for replication of viral DNA. This is a significant finding, suggesting that a point mutation in a single virus gene has a major impact upon likely disease severity during an outbreak.

In 2006, an outbreak of EHV-1 among stables in Florida resulted in the institution of various quarantine measures. The outbreak was determined to have originated with several horses imported from Europe via New York, and then shipped to Florida.