Equine herpesvirus (EHV) infections are ubiquitous in most horse populations in the world. EHV-1 and EHV-4 are responsible for respiratory disease outbreaks, especially in concentrated horse populations. In addition to respiratory disease, EHV-1 can cause late-term abortion in pregnant mares or neurologic disease. These conditions result in economic losses within the horse industry. Since 2000, there appears to be an increase in equine herpesviral myeloencephalopathy (EHM), raising concern that the neuropathic strain of EHV-1 may be an emerging disease. Primary infection occurs in the respiratory tract, where the virus has a predilection for vascular epithelium. Typically, about 10% of infected horses develop EHM during an outbreak. Acute onset of ataxia and weakness are characteristic, appearing 6-10 days after infection, with severity ranging from mild to severe. Other neurologic signs are often present and have a variable rate of progression. Diagnosis is confirmed by PCR testing on samples of nasal secretions, serum, and CSF. There is no specific treatment beyond supportive care. Vaccinations for EHV-1 respiratory disease and abortions are available but do not claim to be protective against the neurologic disease. Latent infections are common, and stressors should be minimized. Management of horse movement on a premise is important to limit the spread of disease. Affected horses should be isolated from those unaffected, and new arrivals should be isolated from the resident population for at least 3 weeks.
Links to sections in the MVM:
Equine Herpesvirus Infection
Vaccination Program for Horses
The Neurologic Evaluation in Horses
References
Gildea S, Sanchez Higgins MJ, Johnson G, et al. Concurrent vaccination against equine influenza and equine herpesvirus — a practical approach. Influenza Other Respir Viruses. 2016 Sep;10(5):433-3. doi: 10.1111/irv.12396
Gonzalez-Medina S, Newton JR. Equine herpesvirus-1: Dealing practically but effectively with an ever present threat. Equine Vet J. 2015 Mar;47(2):142-4. doi: 10.1111/evj.12416
van Galen G, Leblond A, Tritz P, et al. A retrospective study on equine herpesvirus type-1 associated myeloencephalopathy in France (2008-2011). Vet Microbiol. 2015 Sep 30;179(3-4):304-9. doi: 10.1016/j.vetmic.2015.07.003
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