New EHM Outbreak in California

The affected horse resides in Alameda County along with 21 stablemates.
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Alameda County, California
The affected horse resides in Alameda County along with 21 stablemates. | Wikimedia Commons
On Feb. 17, California Department of Food and Agriculture (CDFA) officials confirmed an adult Warmblood gelding in Alameda County with equine herpesvirus myelocencephalopathy (EHM), the neuropathogenic strain of equine herpesvirus-1 (EHV-1). The horse had displayed neurologic signs on Feb. 11 but did not have a fever. He was quarantined at his home premises along with 21 potentially exposed equids on the property.

No horses have moved on or off the property in the past 14 days, and no known epidemiological link to other current EHM cases is known to exist.

CDFA conducted a site assessment and helped implement enhanced biosecurity measures including monitoring temperatures twice daily.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and equine herpesvirus myeloencephalitis (EHM, the neurologic form).

equine herpesvirus
VIDEO | Health Alert: Equine Herpesvirus

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.

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Written by:

Diane Rice earned her bachelor’s degree in agricultural journalism from the University of Wisconsin, then married her education with her lifelong passion for horses by working in editorial positions at Appaloosa Journal for 12 years. She has also served on the American Horse Publications’ board of directors. She now freelances in writing, editing, and proofreading. She lives in Middleton, Idaho, and spends her spare time gardening, reading, serving in her church, and spending time with her daughters, their families, and a myriad of her own and other people’s pets.

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