Fifth US state reports vesicular stomatitis in horses in 2015 season

The tongue of a horse with vesicular stomatitis.
The tongue of a horse with vesicular stomatitis.

Colorado has become the fifth US state in 2015 to report early-season cases of vesicular stomatitis in horses.

The Colorado Department of Agriculture confirmed on Thursday that horses on two Montrose and one Delta County premises had tested positive for the disease and had been placed under quarantine.

Previous positive cases in the 2015 season have been reported in Arizona, New Mexico, Texas and Utah.

Initial investigations into the suspected Colorado cases were carried out by field veterinarians from the State Veterinarian’s Office within the Colorado Department of Agriculture. On July 2, the National Veterinary Services Laboratory reported positive tests on samples submitted from the horses involved.

State veterinarian Keith Roehr said the primary spread of vesicular stomatitis was thought to occur through insect vectors.

“The horses involved in these cases have no history of travel,” he said.

Roehr said vesicular stomatitis can be painful for animals and costly to their owners.

“The virus typically causes oral blisters and sores that can be painful, causing difficulty in eating and drinking.”

The disease proved troublesome in Colorado during the 2014 outbreak, with 556 livestock investigations in the state resulting in 370 quarantines. The final quarantines released in January 2015.

Livestock owners who suspect an animal may have the disease should immediately contact their local veterinarian. Livestock with clinical signs of vesicular stomatitis are isolated until they are determined to be of no further threat for disease spread.

Vesicular stomatitis is a viral infection that can affect horses, mules, cattle, bison, sheep, goats, pigs, and camelids. It also has the ability to infect people, causing flu-like symptoms, but such cases are rare.

Clinical signs include vesicles, erosions and sloughing of the skin on the muzzle, tongue, teats and above the hooves of susceptible livestock. Vesicles are usually only seen early in the course of the disease.

Its transmission is not completely understood, but biting insects are known to be a key vector, and mechanical transmission and livestock movements are also believed to play a part.

The symptoms are similar to those of foot and mouth disease. In cattle, animal health agencies must establish that the symptoms are not a result of foot and mouth disease, which has not been seen in the US since 1929.

Equine epidemiologist Angela Pelzel-McCluskey told Horsetalk in January that the 2014 outbreak fitted the pattern of a bad season every eight to 10 years, with the last outbreak on a similar scale being in 2004-2006. This particular outbreak began in 2004, continued into the following year, and the virus managed to over-winter into 2006.

Before that, there were hundreds of cases reported in 1995 and 1997. There were reports, too, of large numbers of cases in 1985-86.

She believes these major outbreaks occur when climatic and ecological factors combine in a way that favor the insect vectors, although the formula is not necessarily simple.

“We don’t really know which factors are most import important or impactful,” she said.

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