Outbreak of equine herpesvirus type 1 myeloencephalitis.

Lessons from an Australian outbreak of myeloencephalitis affecting five mares

source: M.J.Studdert et al
Veterinary Record vol 153 no 14, October 4 2003
starts p417, 7 pages long

Equine herpesvirus (EHV) type 1 can lead to four syndromes, respiratory problems, abortion and death of foals, and myeloencephalitis, though it may be that not all EHV strains are linked to myeloencephalitis. This study investigates an outbreak involving five pregnant mares from the same paddock on an Australian thoroughbred farm, which were affected by EHV-1 myeloencephalitis. There were a total of 170 horses on this farm, including 74 mares. The symptoms of the affected mares included urinary incontinence and hindlimb ataxia, or not being able to control the back legs. The condition affects the spinal cord rather than the brain.

Risk factors that predispose horses to this disease include pregnancy, lactation, and a build-up in levels of EHV-1 infections in horse populations. Horses that lack specific EHV antibodies also appear to be more at risk, and the affected mares on this farm were more likely to have had low EHV-1 antibody titres, or no EHV-1 antibody titres at all. Vaccination can help protect against abortion and respiratory problems caused by EHV-1, and may protect against myeloencephalitis, though vaccination after clinical signs have been noted may exacerbate the condition.

The farm acted rapidly in notifying the Chief Veterinary Office, and the outbreak was contained with the help of strict hygiene and quarantine measures. The article discusses the outbreak in further detail.