I was recently asked by a client about a case of EHV-1 induced myeloencephalitis (often referred to as Equine Herpes Myeloencephalopathy (EHM) ) reported to have occurred in Santa Barbara County earlier this month. I was able to discuss this case with the veterinarian who performed the postmortem evaluation. It seemed an important topic which warranted an SMEquine Newsletter update. This is what I learned.
The Santa Barbara County case of EHV-1 Myeloencephalopathy did occur in the Santa Ynez Valley and resulted in the euthanasia death of a single mare on March 31, 2012. Laboratory results were reported on April 6, 2012. Upon conclusion of an epidemiological investigation, it was determined that this individual mare had no credible exposure to other horses and had lived in relative isolation prior to the illness and that this infection was unrelated to other cases seen within the state earlier this year. No other cases of the disease have been reported in Santa Barbara Co. in the ensuing three to four weeks.
Laboratory testing at the time of euthanasia revealed the presence of EHV-1 in both the brain and spinal cord. The specific strain of EHV-1 was NOT the strain most commonly associated with the neurologic form of the disease, but was reported to be due to the more common, so called non-neurologic strain.
It is very important to keep in mind that EHV-1 Myeloencephalopathy is considered a disease syndrome and is NOT always associated with a single genotype of the virus (the so called neurotropic strain). This suggests that other factors may also contribute to the onset of this neurologic disease. EHV-1 neurologic disease is primarily caused by a specific neurotropic strain of EHV-1 as identified by PCR testing, however, 15 to 24% of the neurologic cases can be caused by the more common "non-neurotropic" virus as was seen in this case.
With these results in mind, it is considered unlikely that there is any credible threat of future cases of infection associated with this mare's unfortunate disease. It would seem prudent to maintain usual vaccination protocols for protection against the common strains of EHV-1 as is usually recommended with no additional action necessary at this time. Please keep posted for further develops.
See my meeting notes from the UC Davis Equine Herpes Outbreak Seminar in the May, 2011 archive for further details about this syndrome.
EHV-1: Additional Non-Neurologic Case Identified in Calif. | thehorse.com
Follow this link to the California Dept. of Food and Agriculture for a listing of recent cases in the state. CDFA EHV-1 Case List
