Equine Herpes Myeloencephalopathy (EHM) Diagnosed in California Horse, Quarantine Begins

Rodeo Horse in Santa Barbara County Traveled to Two Events

Two notices have been published this week from the California Department of Food and Agriculture. They are reproduced here for your information:

Announcement 1: April 30, 2014

A seven-year-old Quarter horse mare displaying mild neurologic signs has been confirmed positive for the non-neuropathogenic strain of Equine Herpesvirus-1.

This strain of virus is responsible for the more common rhinopneumonitis cases. A small percentage of the non-neuropathogenic infected horses can display neurologic signs compatible with equine herpes myeloencephalopathy, which is a reportable disease in California.

The positive horse has been quarantined and isolated under veterinary care. An investigation has been initiated. CDFA will continue to monitor the situation.

Announcement 2: May 1, 2014

No additional cases. The Quarter horse mare confirmed positive for the non-neuropathogenic strain of EHV-1 is displaying mild neurological signs uncharacteristic of Equine Herpes Myeloencephalopathy (EHM), specifically vestibular signs, abnormal prehension, and hypermetria of the right front for limb.

Additionally, the positive laboratory test results indicated the mare had an extremely low viral load on nasal swab, which indicated a low level of viral shedding from this infected horse.

Based on the low viral load and atypical clinical signs, it is possible that EHV-1 is not the cause of disease in this horse. Out of an abundance of caution, the horse has been classified as case of EHM by CDFA and remains isolated under quarantine.

The epidemiologic investigation reveals this barrel racing mare did participate in the Clovis Rodeo on Friday, April 25, 2014 and immediately following her run was shipped out to the Springville Rodeo where she did not compete.

Concerned owners of horses that participated in these events can monitor their horses for clinical signs and take temperatures twice daily. Any temperature over 102F should be reported to a veterinarian for investigation.

At this time there is no epidemiologic link to other EHV-1 positive horses recently detected in other states. CDFA continues to monitor the situation.

On May 2, California authorities stated that there were no new cases in that state.




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