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Vesicular stomatitis virus outbreak continues across Wyo, poses livestock health threat

by Wyoming Livestock Roundup

Horse herds across Wyoming have been hit with vesicular stomatitis virus (VSV), and Wyoming State Veterinarian Jim Logan told the Joint Agriculture, State and Public Lands and Water Resources Committee on Sept. 14 that 60 verified cases have been hit with VSV since July. 

Confirmed reports of the virus have been seen in Fremont, Sublette, Albany, Converse, Goshen and Platte counties, he noted.


“Owners seem to be doing alright with it,” Logan said of the Sublette cases. “The animals are doing well, and many are well on their way to healing.”

The owners were concerned when they saw lesions in an animal’s mouth or saw them slobber, he said, calling their vets who contacted the Wyoming Livestock Board (WLSB). After VSV is identified, herds are then quarantined for two weeks.

Quarantines are “relatively short-lived unless new animals develop lesions, which would reset the quarantine clock another two weeks,” Logan said. “The quarantines are set from the time of the first report.”


Slobbering, blisters, sores and sloughing of skin in the mouth, on the tongue or muzzle, inside the ears and on the coronary band above the hooves are major symptoms and lameness and weight loss might result, he said.

“I have seen many animals lose condition during the course of the disease because many will refuse to eat and drink,” Logan related.

Although symptoms closely resemble those for foot-and-mouth disease (FMD) and VS is “clinically indistinguishable” from FMD, it isn’t transmitted as much by contact as it is by flying insects such as deer and horse flies and biting midges, Logan said.

He said, “Introduction of the disease most likely has resulted from the insect vectors either recently arriving on wind currents or having overwintered in the area. This is the most efficient way for the virus and infection to spread. Lateral transmission, or transmission from one infected animal to another susceptible animal, does occur, but that is not the most efficient route of spread.”

Rarely fatal

Because of the similarity to FMD, it is essential to confirm a diagnosis with lab tests, Logan adds. VSV is rarely deadly for horses and mules, he added.

“There have been a few cattle that have died of VSV in Platte and Goshen counties, so the disease can be deadly,” Logan said. “It just usually is not.”

The virus can pop up “anyplace where the insect vectors – biting flies and midges, can survive and live,” Logan said. “Historically we have seen the disease in numerous Wyoming counties including Sublette.”

VSV is considered a cyclic disease, according to Logan, “meaning that it seemed to appear about once every eight to 10 years. That has seemed to change lately with some states such as Texas and Colorado having seen it for the past three years.”

Cases are also reported in New Mexico, South Dakota, Utah and Arizona.

No treatment

Logan said there is no real medical treatment for VSV-infected animals.

“An animal’s immune system is the only cure, and it may take several days for the immune system to build the defenses to get the virus out of the animal’s system,” he explained. “Some veterinarians may treat affected animals symptomatically to help alleviate the symptoms and boost the immune system. This may include vitamin B complex, antibiotics to ward off secondary bacterial infections and anti-inflammatory drugs to reduce the inflammation and pain.”

“Otherwise, TLC is about the best thing that can be done,” he said.


“Insect control is the best preventative measure,” Logan said. “Livestock owners should do whatever they can to reduce insect populations and presence around their animals.”

Horse and livestock owners should keep their animals on higher ground, away from riparian and boggy areas. 

“Many of our previous cases, historically, have originated on places where livestock was held on river bottoms and marshy areas. Avoid this if possible,” Logan advised.

“My advice to livestock owners is to not get paranoid about this disease but to stay vigilant and observant,” Logan said. “Avoid close contact with other animals at events. Don’t share water and feed tubs. Don’t share tack.”

The recent Wyoming State Fair was VSV-free with a lot of advance publicity and health certificates required.

“We watched very closely at the Wyoming State Fair for any sign of VSV,” Logan said. “Wyoming Livestock Board staff veterinarians monitored the livestock barns and shows several times daily all week at state fair, and no sign of the disease was seen there.”

Anyone who suspects an animal has VSV should contact a veterinarian immediately.

This article, in part, ran in the Aug. 21 edition of the Sublette Examiner. Joy Ufford is editor of the Sublette Examiner. Saige Albert, managing editor of the Wyoming Livestock Roundup, provided updates from mid-September. Send comments on this article to

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