In a webinar on 31 May 2023 USDA equine epidemiologist Dr. Angela Pelzel McCluskey said the viral disease is believed to have spread north from Mexico into areas of California having received the heaviest rainfall in decades.

"This is likely supporting vectors," she said.

The Southwestern and Western U.S. have experienced many vesicular stomatitis outbreaks, the most recent and largest outbreak occurred in 2015, USDA officials said. Outbreaks usually occur during the warmer months, often along waterways. The time from exposure to the onset of clinical signs is 2-8 days, the USDA reported.

About vesicular stomatitis
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The Equine Network say clinical signs of vesicular stomatitis in
animals include:
- Vesicle formation leading to ulcerative lesions on the lips, muzzle,
nostrils, and tongue. The tongue is often the most severely affected
area.
- Ulceration of the inner surface of the lips.
- Crusting of the muzzle, nostrils, and/or inside the ears.
- Excessive salivation secondary to the oral lesions.
- Difficulty picking up and chewing feed.
- Lameness due to painful erosions on the coronary band.
- Lesions can occur on the udder, sheath, and inside of the ear.
- Lesions can develop secondary infections resulting in slow-to-heal
wounds.
- Animals on pastures are at increased risk of vesicular stomatitis.

CANADIAN HORSES, SWINE AND RUMINANTS RETURNING TO CANADA will not be able to enter Canada after a stay in a VS infected state in the last 21 days. The exception to this rule is Canadian Animals returning on their Canadian health certificate can do so up to three (3) days after the state they are in has been declared affected by vesicular stomatitis by USDA and must be inspected by the CFIA POE vet. Otherwise, the Canadian health certificate is null and void. Horses, swine and ruminants in infected VS states will have to be moved to a non-infected state, stay there for at least 21 days and be certified by USDA.