There has been a recent outbreak of neurologic herpes virus (Equine Herpes Myeloencephalopathy or EHM) confirmed in the Pleasant Hill area. This resulted in the death of one severely affected horse and the quarantine of the barn. Currently, there are no other barns known to be affected.
Equine Herpes Virus 1 (EHV-1) is among the most common infectious diseases in horses. It more often causes a contagious respiratory disease known as rhinopneumonitis. It also can cause abortions in mares. Rarely, it is a more serious disease affecting the central nervous system. Unfortunately this can lead to progressive ataxia (incoordination) and complete recumbency (inability to rise).
Transmission usually occurs from infected horses through nasal secretions, placental tissues, and fomites (objects). The virus is fragile, does not live well outside the equine body, and is easily disinfected. Infected horses can shed virus from day one post infection but usually stop shedding virus within 2 to 3 weeks. Amount of virus shed has a lot to do with the host animal's immune system status.
Equine herpes virus is very much like other mammalian herpes viruses in that animals are infected at a very young age and then remain latently infected for life. In times of stress or in pregnancy the virus can recrudesce and horses will actively shed virus and infect other animals.
NEUROLOGIC FORM and CONTROL MEASURES
Probably a genetic mutation or variation in EHV- 1 has made it more pathogenic for the central nervous system in the last few years. The last major outbreak of EHM occurred in Ogden, Utah at the National Cutting Horse show in 2011 resulting in 13 dead horses.
It would be good practice to institute bio-security measures in all training and stabling facilities for the near future. This would include monitoring temperatures two times per day on all horses that have traveled recently. Fever usually precedes the onset of neurologic signs in infected horses approximately four days. The febrile phase coincides with active viremia when the horses are most infective to others.
New arrivals or horses showing fevers should be isolated from the main population until an accurate diagnosis is established.
Vaccination protocols: Vaccinations for EHV-1 have been somewhat controversial.Some have suggested that the over vaccinating with in activated rhino products, such as those found in 5 way vaccines may actually have contributed to the development of neurologic infections in horses. This is because they have not been proven to induce a cell mediated response which is thought to be more important in controlling neurologic infections.
This newest outbreak serves as another reminder as the importance of instituting routine vaccination programs and bio-security measures with the guidance of your veterinarian. Our routine vaccination programs can be found on our website on the following link:
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Please call if you have any questions.