The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service recently issued the following alert, which was reportedly updated on November 3:

On October 31, 2025, the National Veterinary Services Laboratories in Ames, Iowa, confirmed findings of vesicular stomatitis New Jersey virus (VSNJV) in horses on two separate premises in Cochise County, Arizona.

The cases

One horse, a 21-year-old grade mare on the first premises met confirmed vesicular stomatitis virus (VSV) index case definition with compatible clinical signs and viral genome sequence data indicative of VSNJV on swabs from oral lesions. There are an additional 52 horses and 120 cattle on the first premises. They are not clinically affected.

On a second premises in Cochise County, Arizona, one horse, an 8-year-old Quarter Horse gelding, met confirmed VSV index case definition with compatible clinical signs and viral genome sequence data indicative of VSVNJ on swabs from oral lesions.

There are an additional six horses and 60 cattle on the second premises. They are not clinically affected. These two premises are the 2025 VSV index cases for the United States.

The last outbreak of VSV in the U.S. occurred from May 2023 through January 2024. There were a total of 319 premises affected in three states (California, Nevada and Texas).

About VSV

According to the USDA APHIS website, vesicular stomatitis is “a contagious disease of livestock, mainly affecting horses and cattle. Occasionally, this disease can infect swine, sheep, goats, llamas, alpacas and even people. It is primarily transmitted by biting flies and midges. The disease causes blister-like sores, among other side effects.”

Although vesicular stomatitis rarely causes high mortality rates, it can impact animal movement and international trade. This can result in economic losses for livestock producers. Outbreaks usually occur during warmer months, often along waterways. The southwestern and western United States have experienced several outbreaks since 1995, with the most widespread in 2019.

Vesicular stomatitis virus circulates annually between livestock and insect vectors in southern Mexico. It only occasionally results in incursion to the U.S. when climatic and ecological factors support movement of VSV-infected insect vectors northward.

Known vectors

Known competent vectors for transmission of VSV include black flies, sand flies and biting midges (Culicoides spp.). The initial epidemiological investigations on both VSV-confirmed positive premises in Cochise County, Arizona, indicate that incursion of VSV-infected insect vectors is the likely source of infection on these premises.

There have been no recent livestock movements on or off either premises. Biosecurity measures and
vector mitigation on the affected premises have been instituted to reduce within-herd spread of the virus. The susceptible livestock species are being monitored, and both VSV-positive premises will remain under state quarantine until 14 days from the onset of lesions in the last affected animal on the premises.

For more information about signs of VSV, as well as how to prevent it and treat it, click here.