EDCC Latest Updates on EHV-1 Outbreaks in California

The Equine Disease Communication Center (EDCC) is closely monitoring multiple equine herpesvirus (EHV-1) outbreaks in California.

As of February 28, the following California counties have confirmed EHV-1 cases (some neurologic):San Mateo, Riverside, Santa Barbara and Ventura. iStock

The Equine Disease Communication Center (EDCC) is closely monitoring the equine herpesvirus (EHV-1) outbreaks in California. EHV-1 most often causes a respiratory disease, which is usually mild and self-limiting, but the infection occasionally leads to the life-threatening neurologic disease equine herpesvirus myeloencephalopthy (EHM).

As of February 28, the following California counties have confirmed EHV-1 cases.

San Mateo County: A total of 28 horses have been confirmed positive on this premises. Three EHM cases (EHV-1 positive with neurologic signs) and 25 EHV-1 febrile-only cases have been confirmed. The California Department of Food and Agriculture (CDFA) continues to actively monitor the situation.

Riverside County: A second outbreak in California is associated with the Desert International Horse Show. To date, 21 horses have been confirmed positive. Three confirmed EHM cases (EHV-1 infection with neurologic signs) and 18 confirmed EHV-1 fever-only cases are associated with this incident. CDFA continues to monitor the situation.

An additional three horses that had attended the event in Riverside County and had subsequently returned to their home premises—displaying fever only with no neurologic signs—were confirmed positive for EHV-1. The horses are located in Santa Barbara, Ventura and San Mateo counties. The positive horses have been isolated and will be quarantined on their home premises, along with any exposed cohorts.

Orange County: Two horses have been confirmed positive on this premises. A 16-year-old Warmblood mare in Orange County displaying neurologic signs on February 22 was confirmed positive for equine herpesvirus myeloencephalopathy (EHM) secondary to equine herpesvirus-1 (EHV-1 non-neuropathogenic strain) on February 24. The horse was euthanized due to the severity of the clinical signs. Additionally, a 10 year-old Warmblood gelding on the same premises displaying fever only with no neurologic signs was confirmed positive for EHV-1 on February 24. The febrile gelding was part of a cohort of horses that attended the event premises in Riverside County that has an active EHM incident, and the neurological mare was exposed to the cohort of horses returning to the home premises from the event in Riverside County. Eighty-six exposed horses on the home premises have been isolated and quarantined. CDFA will continue to closely monitor this situation.

Los Angeles County: A 20-year-old Warmblood gelding in Los Angeles County displaying neurological signs on February 22 was confirmed positive for EHM secondary to equine herpesvirus-1 (EHV-1 non-neuropathogenic strain) on February 24. The horse was euthanized due to severity of clinical signs. This gelding attended a show in Los Angeles County last week and event management has been notified. An investigation is pending to determine if this incident is epidemiologically linked to any other active EHM incidents. The exposed horses on the gelding’s home premises have been isolated and will be quarantined. CDFA will continue to closely monitor this situation.

If you are in an area of a suspected outbreak, horse owners and participants of all competitions should practice the following biosecurity and best practices:

  • Limit horse-to-horse contact
  • Limit horse-to-human contact
  • Avoid use of communal water sources
  • Monitor your horse for clinical signs of disease, take temperatures daily and report any temperature over 102°F to a veterinarian

For the latest information about Equine Herpesvirus visit https://equinediseasecc.org/disease-information/equine-herpesvirus and keep up to date on information about equine infectious disease by signing up for email alerts or downloading the EDCC Disease Alert app by searching “EDCC Disease Alerts” at the App Store or Google Play Store.

About the Equine Disease Communication Center

The EDCC is an industry-driven information center which works to protect horses and the horse industry from the threat of infectious diseases in North America. The EDCC is based in Lexington, Ky., at the American Association of Equine Practitioners’ headquarters, with a website and call center hosted courtesy of US Equestrian. The EDCC is funded entirely through the generosity of organizations, industry stakeholders and horse owners. To learn more visit www.equinediseasecc.org or sign up for the latest disease alerts.

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