Disease Du Jour: Vesicular Stomatitis

The outbreak of vesicular stomatitis in horses this year has caught horse owners and veterinarians by surprise.
Vesicular stomatitis map quarantined premises thru 7-13-23
USDA map showing all counties that had vesicular stomatitis premises quarantines through July 13, 2023. Courtesy USDA APHIS

Many people are seeing information about vesicular stomatitis virus (VSV) cases in California and Texas this year. We discussed this situation with Angela Pelzel-McCluskey, DVM, MS, is a National Equine Epidemiologist for the USDA’s Animal and Plant Health Inspection Service, Veterinary Services. She had some insightful information for equine veterinarians in this episode of the Disease Du Jour podcast.

2023 Vesicular Stomatitis Outbreak Stats

Since the start of the 2023 vesicular stomatitis outbreak on May 17 and through July 13, 123 vesicular stomatitis virus-affected premises have been identified. Those were comprised of 42 confirmed positive premises and 81 suspect premises in two states—California and Texas.

A total of 120 of these premises have had only equine species clinically affected.

Two premises have had clinically affected cattle (both in San Diego County, California). One premises has had a clinically affected rhinoceros (in San Diego County, California). (Editor’s note: Horses and rhinos are considered to be related far back in evolution.)

Vesicular Stomatitis and Horses

“The virus causes nasty lesions on the muzzle, nose, ears, coronary bands, sheath and teats,” said Pelzel-McCluskey. “Horses can heal with supportive care. It takes several weeks for the lesions to heal.”

Horses can get blisters in and around their mouths, which make them not want to eat, noted Pelzel-McCluskey.

While it is an uncomfortable disease for the animals, there are other important ramifications to consider with vesicular stomatitis. One is that the disease can be spread to humans.

“Vesicular stomatitis can be transmitted to humans by handling lesions in the horse,” she said. Pelzel-McCluskey reminded veterinarians that if horses have oral lesions and they “blow’ or snort, the virus can be spread. “Keep your face away from the horse,” she advised.

“The virus can be transmitted through direct contact and in shared feed and water,” Pelzel-McCluskey explained. “You don’t want to spread the virus by moving horses.”

Others ramifications include trade, transport and competition regulations.

“Restricted movements” are common during a vesicular stomatitis outbreak, noted Pelzel-McCluskey. The disease can cause “trade ramifications” with livestock moving to other countries.

Restrictions also are often put in place for individual equine competitions. Knowing the different rules for each competition or facility can make it difficult for equine veterinarians to help horse owners meet guidelines for entry onto the show grounds.

Prevent Vesicular Stomatitis Transmission

Veterinarians need to advise horse owners to practice good biosecurity with their horses to prevent the spread of virus. Important in that is vector control.

“There are three main vectors: black flies, sand flies and biting midges,” said Pelzel-McCluskey.

She said climate change is contributing to vesicular stomatitis spreading in California.

“We are not protected by historic geography,” noted Pelzel-McCluskey. That means that the rains in the previously dry/desert region are allowing for vector spread.

“Climate affects where vector-borne diseases affect us,” she stated.

About Angela Pelzel-McCluskey, DVM, MS

Angela Pelzel-McCluskey, DVM, MS, is a National Equine Epidemiologist for the United States Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS), Veterinary Services. She is based in Fort Collins, Colorado. 

Editor’s note: Follow the outbreak reports on the EDCC Health Watch articles available on EquiManagement’s website and social media.

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