California Horse Positive for EHM


On November 30, a 22-year-old Quarter Horse mare in Contra Costa County, California, was confirmed positive for equine herpesvirus myeloencephalopathy (EHM) secondary to EHV-4. The female developed clinical signs, including ataxia, fever, and anorexia. He is currently alive and under veterinary care at an offsite veterinary hospital. Fourteen potentially exposed horses in the home area were quarantined on December 1.

EDCC Health Watch is an Equine Network marketing program that uses information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization supported by industry donations to provide open access to infectious disease information.

EHV 101

Herpesvirus is highly contagious in horses and can cause a variety of diseases in equids, including rhinopneumonitis (a respiratory disease commonly seen in young horses), abortion in broodmares, and EHM.

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In many horses, the first or only sign of EHV-1 infection is fever, which may go unnoticed. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a runny nose. Pregnant mares usually show no signs of infection before they abort, and abortions usually occur late in pregnancy (about eight months) but can occur earlier. Abortion can occur anywhere from two weeks to several months after infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and may show signs of respiratory infection. After a few days, neurologic signs such as ataxia (incoordination), weakness or paralysis of the front and rear limbs, urinary retention and dribbling, loss of tail tone, and recumbency (inability to rise).

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Herpesvirus is easily spread through nose-to-nose or close contact with an infected horse; sharing contaminated equipment, including towels, buckets, and towels; or the clothing, hands, or equipment of people who have recently been in contact with an infected horse. Standard biosecurity measures, including hygiene and basic cleaning and disinfection procedures, should be in place at all times to help prevent the spread of disease.

Current EHV-1 vaccines may reduce viral shedding but do not protect against the neurologic form of the disease. Implementing standard biosecurity practices is the best way to reduce the spread of the virus, and the best way to prevent disease is to avoid the disease.

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