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By Miriam Raftery

June 4, 2023 (San Diego) – The outbreak of Vesicular Stomatitis  Virus (VSV) that started last month in San Diego County has now spread to San Bernadino as well as Riverside County. There are now 44 properties quarantined, including 28 in San Diego County, according to the latest update posted  June 2, 2023 by the U.S. Dept. of Agriculture.

Since the last report a week earlier, 18 new properties affected by VSV have been identified, including three new confirmed positive cases and 8 suspected cases in San Diego County.

To date, all of the premises quarantined have cases in horses or other equine species, except one property that has clinically affected cattle locally. However the disease can occur in other animals such as llamas, alpacas, pigs, sheep, goats and deer.

It can also spread to humans, though in people it normally produces severe flu-like symptoms, instead of the blister-like lesions characteristically found on the mouths, noses, hooves or other areas in afflicted livestock.

The disease is spread through bites by insects such as black flies, sand flies and midges, but can also be transmitted through shared food or water, or on commonly touched surfaces. While the disease is rarely fatal, it can be debilitating for animals and can also disrupt events such as horse shows.

In a webinar on May 31, Dr. Angela Pelzel McCluskey, USDA equine epidemiologist, said the disease is believed to have spread north from Mexico into areas of California that have received the heaviest rainfall in decades. “This is likely supporting vectors,” she said.

When VSV is confirmed or suspected at a site, the USDA is mandating quarantine of all susceptible species, isolation of animals with lesions, enhanced biosecurity measures, and vector mitigation to reduce spread within herds. Quarantines last for at least 14 days from onset of lesions in the last affected animal on the premises.

Chart, right: U.S. Dept. of Agriculture

While the USDA has not disclosed precisely where the most recent cases have occurred, local veterinarians have confirmed to the Ramona Sentinel and San Diego Union Tribune that earlier cases included Ramona, Lakeside, Campo, Jamul, Del Sur, and Descanso.

The U.S. Equestrian Foundation has implemented new biosecurity protocols(link is external) required of all equine competitions by June 1. 

This approach is less stringent than back in 2022, during an outbreak of equine herpes virus-1, an often lethal virus that forced cancellation of  competitions.

Under the new USEF requirements, a veterinarian must examine all horses from outbreak-affected states on arrival and will bar entry if symptoms are evident.  While onsite, the horses must have twice-daily temperature recordings and monitoring for vesicles,or lesions. Horses that develop fevers over 101.5 and/or vesicles will be isolated until the horse can be moved off the premises.

Some states or venues may restrict entry of animals from counties with VSV quarantines, so be sure to check with the location before traveling with your horses or other livestock.

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