Riverside County EHV Cases Spread to Three Other Counties

California officials continue to monitor the outbreak on-site at the index premises.

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Riverside County EHV Cases Spread to Three Other Counties
California officials continue to monitor the outbreak on-site at the index premises. | Photo: Wikimedia Commons
On Feb. 23, California Department of Food and Agriculture (CDFA) officials confirmed three more horses with equine herpesvirus-1 (EHV-1).  The horses had attended an event at a Riverside County venue earlier in the month and were quarantined there with more than 40 other attendees in their barn. They had subsequently returned to their home premises in Santa Barbara, San Mateo, and Ventura counties, where they have been isolated and under quarantine along with any other exposed horses in their cohort.

Three other horses on the index (event) premises, which were stalled outside the venue’s quarantine barn, displayed fever but no neurologic signs and were confirmed positive with EHV-1.

Since the outbreak began, officials have confirmed three equine herpesvirus myeloencephalopathy (EHM) cases (EHV-1 positive with neurologic signs) and 16 cases with fever only (EHV-1).

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 EHM.

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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