After nearly five years of being VS free, Vesicular Stomatitis is exploding across large areas of Texas with the count up to nine counties with confirmed cases this year, mostly in equine. The latest confirmations include two cases of bovine infection as well.

On July 30 the Texas Animal Health Commission reported 14 new premises have been found with one or more animals confirmed with Vesicular Stomatitis virus (VSV), all but one in Central Texas, including 12 premises in Bastrop County and one additional premise in Travis County. The remaining premise was located in Val Verde County near Del Rio.

On July 25 eight new cases of VSV were reported in Central Texas, including five premises in Travis County and three new premises in Bastrop County.

The latest round of confirmed premises raises the total number reported this year to 35 sites. Affected counties include: Kinney, Hidalgo, San Patricio, Nueces, Jim Wells, Bastrop, Travis, Guadalupe and Val Verde counties. Six premises have been released from quarantine: one in Kinney County, two in Nueces County, two in San Patricio County and one in Hidalgo County.

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Large number susceptible

According to the USDA-APHIS weekly VS update, so far this year 50 horses and four head of cattle have tested positive for VS New Jersey serotype. Forty of those animals remain in quarantine while 10 have recovered.

A large number of other animals in Texas have been or remain susceptible to VS infection according to the USDA-APHIS report, including 388 horses, 1,855 cattle, three pigs, and 30 goats. These numbers include all infected animals so far this year.

Also of major concern are reports coming out of Colorado where confirmed VS cases are on the rise. Colorado animal health officials are reporting a total of 37 horses across four counties have tested positive for VS over the last 10 days, representing the first cases reported outside of Texas this year.

Infected animal are quarantined for a period of no less than 21 days and monitored by state animal health officials. After the quarantine expires, and provided the animals show no further symptoms or signs of VS, the premise is released from quarantine.

Animal health officials offer no particular reason why this year's outbreak of VS has occurred so fast and in such large numbers. Phlebotomine sandflies, which have been confirmed biological vectors of VSV, can spread the virus, but of most concern in the Southwest are Culicoides midges and Simulium blackflies.

However, VSV can also be spread by direct contact between infected animals and also through watering and feed troughs and buckets. While rare, human contact with an infected animal can transfer the virus to humans and to other animals; the virus is much less severe in humans and generally causes only flu-like symptoms.

Ten-year cycles

Outbreaks of VS in the U.S. are thought to occur repeatedly across the Southwest over 10 year cycles, with disease outbreaks continuing for 2 to 3 consecutive years and then disappearing again for 10 years or more before returning. Researchers are uncertain why the lifecycle of the virus is so sporadic or why some years the outbreak is more severe than in other years.

"What we're seeing now is a typical recurrence of Vesicular Stomatitis and the large number of cases is not really that unusual," said Dr. Terry Hensley, assistant agency director at the Texas A&M Veterinary Medical Diagnostic Laboratory in College Station. "VS will crop its head up every 10 years or so and can demonstrate large numbers of animals that become infected. While research continues, we suspect this cycle has a lot to do with ideal weather conditions that support the gnats and other insects that can distribute the virus."

Animal health officials say control depends on rapid recognition of initial cases, quarantine, and restriction of movement of infected and in-contact animals, and insect control. No commercially-available VSV vaccines are available in the U.S., but an autologous vaccine was made in 1995 to help control that outbreak. Several inactivated vaccines containing both the Indiana and New Jersey serotypes are used in Central and South America.

Viral disease

Vesicular stomatitis is a viral disease that primarily affects horses and cattle but can affect sheep, goats, llamas, alpacas, swine, deer and some other species, including bobcats, raccoons and monkeys. Animals infected with the disease can usually be clear the virus and its lesions within a period of 21 days or less. The virus is not fatal to infected animals.

In the past decade, the Southwestern and Western United States experienced several VS outbreaks, usually during the warmer months, often along waterways. In some years, only a few premises in a single state have been affected. However, in other years, multiple states and many premises have been involved.

So far this year, only one other state, Colorado, has reported VS cases.

At first glance, blisters, erosions in the mouth, excessive salivation, or crusty sores around an animal’s muzzle, teats or hooves resemble the dreaded and highly contagious foreign animal virus, Foot-and-Mouth Disease (FMD). FMD has not been detected in the U.S. since 1929, but animal health officials and ranchers remain on guard for an accidental or intentional introduction of the disease.

Sick animals should be isolated and may need supportive care to prevent a secondary infection where blisters have broken. Painful lesions also can form around animals’

hooves, resulting in temporary lameness. Ranchers, veterinarians and others who handle sick animals should wear rubber or latex gloves as a biosecurity measure to prevent spread of disease to other animals, or to themselves.

Reporting requirements

Confirmed cases of VS must be reported to interstate and international trading partners, which may result in restrictions, additional inspections or testing requirements.

The following link provides a list of states that have notified the TAHC of enhanced entry requirements they are imposing on Texas livestock (including horses) due to the recently announced VS cases in Texas. This information is not intended to be the final answer for producers wishing to move animals. Prior to movement, animal transporters should contact the state of destination for interstate questions. For international export requirements, contact the USDA Veterinary Services (VS) Austin office at (512)-383-2411, or Dr. Byron Schick, USDA Service Center 4 Director in Oklahoma City at (405)-751-1701.

The latest information about restricted movement to other states can be found here.