This summer’s outbreak of vesicular stomatitis (VS) has affected 722 premises as of October 28, according to the USDA’s Animal and Plant Health Inspection Service (APHIS). Confirmed cases have occurred in eight states – Arizona, Colorado, Nebraska, New Mexico, South Dakota, Texas, Utah, and Wyoming. Currently, there are 131 affected premises remaining under quarantine in six states including Colorado, Nebraska, New Mexico, South Dakota, Utah, and Wyoming.

Last week’s situation report from APHIS listed 57 new VS-affected or suspected premises since the previous report on Oct. 21.

VS is a reportable disease and positive identification results in quarantine of the affected premises until the disease clears.

After a relatively mild fall season, weather forecasts suggest colder temperatures will move into much of the VS-affected region over the next week. Freezing temperatures should kill off the insect vectors that spread the virus, and new cases should decline during the coming weeks.

Colorado has seen the most cases so far this year, with 364 premises in 32 counties affected. This summer’s index case occurred on April 29, with a confirmed finding of VS in a horse in Grant County, New Mexico. Most confirmed cases of VS have involved equine premises, although the disease does affect cattle.

Last summer, a total of 435 VS-positive premises were confirmed in four U.S. states including Arizona Colorado, Nebraska and Texas.

The virus is spread primarily by insect vectors, and thus tends to disappear during the winter in temperate climates and break out during the summer, particularly in areas where wet conditions encourage insect populations.

Vesicular stomatitis virus (VSV) is classified as a rhabdovirus, and there are two serotypes,  New Jersey and Indiana. Outbreaks this year have involved the New Jersey serotype. Infection with one serotype is not cross-protective for the second serotype. Clinical signs of VS, which can affect equines, cattle, bison, sheep, goats, pigs and camelids include vesicles, erosions, and sloughing of the skin on the muzzle, tongue, teats and above the hooves. Clinical signs of VS can appear similar to those for foot and mouth disease, increasing the importance of diagnosing and reporting suspicious cases.

Insect vectors are the primary source of transmission of VS although mechanical transmission occurs in some species. Fly control is a key component in preventing spread of the virus.

Rarely, VS can affect humans, typically those who are in contact with infected animals. In humans the disease typically causes flu-like symptoms. 

 According to APHIS, when a definite diagnosis is made on a farm, veterinarians and producers should take the following steps:

·         Separate animals with lesions from healthy animals, preferably by stabling. Animals on pastures tend to be affected more frequently with this disease.

·         As a precautionary measure, do not move animals from premises affected by vesicular stomatitis until at least 21 days after lesions in the last affected animal have healed.

·         Implement on-farm insect control programs that include the elimination or reduction of insect breeding areas and the use of insecticide sprays or insecticide-treated eartags on animals.

·         Use personal protective measures when handling affected animals to avoid human exposure to this disease.

APHIS offers weekly VS updates and information on the disease on its vesicular stomatitis website