Equid alphaherpesvirus 1, formerly 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 ), however its efficacy is questionable. The virus varies in severity from sub-clinical to very severe. Most horses have been infected with EHV-1, but the virus can become latent and persist without ever causing signs of infection. In 2006, an outbreak of EHV-1 among stables in Florida resulted in the institution of quarantine measures. The outbreak was determined to have originated in horses imported from Europe via New York, before being shipped to Florida. Strains Two main strains of EHV-1 have been isolated. D752 strains are correlated to outbreaks associated with neurological disease, whereas outbreaks with non-neurological disease are more closely associated with strains of N752. However, not all horses infected with D752 strains develop neurological disease; conversely, some horses infected with N752 strains will develop neurological disease. A mutation results in both these two different main strains, D752 is the presence of aspartic acid and the N752 is the presence of asparagine. 80–90% of neurological disease is caused by the D752, and 10–20% for N752. The disease caused by neurological strains has been named Equine Herpesvirus Myeloencephalopathy or EHM. There is currently no licensed vaccine against EHM and no treatment other than palliative care. The disease rose to worldwide public prominence in early 2011, due to an outbreak centered on the National Cutting Horse Association (NCHA) Western National Championships held in Ogden, Utah from April 29 to May 8, 2011. The outbreak lasted approximately two months, generating 90 confirmed cases of the disease, spread over 10 American states, and resulting in the deaths of 13 horses before it was declared contained by the US Department of Agriculture. Latency The EHV-1 virus can latently infect horses and can reactivate if appropriate conditions appear. These conditions include high levels of stress, immunosuppression, transportation,