EHM Emerges in the Region


Equine herpesvirus myeloencephalopathy (EHM) has been confirmed recently in horses in several states, including Idaho, Arizona, Nevada, California and Iowa.

Owners of horses that have traveled in those areas recently are being advised to keep their horses in isolation for two weeks and monitor for clinical signs, which include: fever, nasal discharge, depression, incoordination, hind limb weakness, loss of tail tone, loss of bladder tone, dog sitting position, and inability to rise.

Laboratory confirmation of a Johnson County horse infected with EHM, was received by Wyoming Livestock Board (WLSB) staff veterinarians on Thursday, April 4. The horse has been quarantined to its premise in Johnson County with 19 other horses.

The affected horse began showing neurologic signs, including hind-end weakness, on Wednesday, April 3. It is not known where this horse contracted the disease, but it had been at college rodeo events on March 15-16 at the Cam-plex in Gillette and March 21-24 at the Goshen County Fairgrounds in Torrington.

According to WLSB staff veterinarians, equine herpesviruses are very common DNA viruses in horse populations worldwide. The great majority of horses are exposed to EHV1 – the virus that causes EHM – early in life and will become life-long latently infected, meaning they will show no external signs of illness. However, the virus can be reactivated during times of stress such as strenuous exercise, over-exertion, long-distance transport, or at weaning.

There has been a marked increase in the number of EHV1/EHM cases in the U.S. in recent years. Owners who plan on taking their horses to events can help prevent spread of the disease by practicing proper biosecurity measures. This includes not sharing equipment such as water/feed buckets and tack. They should also isolate their horses if they suspect them of being sick, and not allow them to leave the premise until cleared by a veterinarian.

Although highly infectious and contagious among horses, EHM poses no threat to human health.

Note: Check state regulations on animal health as you may need to provide a certificate of health for animals before entering that state or competitions. Contact your local veterinarian with any questions or concerns regarding this disease or any other health concerns with your livestock.


North Dakota Department of Agriculture

Wyoming Livestock Board

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