Animal health officials in Texas and Colorado are hoping for a short summer and an early autumn, the only apparent hope to slow the spread of a nagging Vesicular stomatitis (VS) outbreak that has spread wildly in Colorado and Texas in recent weeks.

VS, a virus with symptoms similar to the more serious and dreaded hoof and mouth disease, is a naturally occurring animal illness that shows up every five years or so across the American Southwest, possibly wintering in northern Mexico just south of the Texas and New Mexico state lines.

"It's not unusual to find VS every few years, mostly in New Mexico and occasionally spreading into Colorado and Texas, but we haven't seen a case in Texas for several years," said Dr. Terry Hensley, assistant agency director at the Texas A&M Veterinary Medical Diagnostic Laboratory in College Station. "How it comes and where it goes remains under research, but we think weather conditions like we experienced last fall and into the spring season this year may have a lot to do with it being vectored by gnats and flies that can broadcast the virus over large areas."

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VS emerged this year near Del Rio in southwest Texas. The National Veterinary Services Laboratories (NVSL) in Ames, Iowa, confirmed a finding of vesicular stomatitis virus (VSV) infection (New Jersey serotype) on an equine premises in Kinney County May 23. Four affected horses on the premises met the case definition of infection with compatible clinical symptoms.

Rapid spread

Very quickly VS spread south along the Rio Grande when two premises were confirmed in Hidalgo County, followed a week later by two additional cases in the Coastal Bend in San Patricio County. By the middle of July, 13 premises in eight Texas counties had been confirmed with VS. Affected counties included Kinney, Hidalgo, San Patricio, Nueces, Jim Wells, Bastrop, Travis and Guadalupe counties.

On July 17, the National Veterinary Services Laboratories in Ames, Iowa, confirmed findings of vesicular stomatitis virus (VSV) infection (New Jersey serotype) on two equine premises in Weld County, Colorado. These were the index cases for Colorado. Three affected horses on one premises and one affected horse on the other premises met the case definition of VSV infection with compatible clinical signs.

From the middle of July through this week, the spread of the virus seemed to accelerate. At the end of last week, the Texas Animal Health Commission (TAHC) confirmed 12 new cases of Vesicular stomatitis (VS) in Central Texas, one in cattle and the rest in horses. The ten new premises are located in Bastrop County. Two new premises are in Williamson County, the first case reported in this county.

Colorado cases increasing

Meanwhile, the spread of cases in Colorado took a sharp turn up in recent days. On Aug. 13 USDA-APHIS reported 33 horses and two (2) cattle cases were confirmed in Boulder County, two horses were confirmed in Broomfield County, four horses in Jefferson County, 22 horses in Larimer County, and 29 additional horses in Weld County.

A cumulative count of animals confirmed with VS in both states now stands at 186 VSV-positive premises that have been identified, 133 premises in Colorado and 53 premises in Texas.

Eight counties are affected in Colorado (Adams, Boulder, Broomfield, Douglas, El Paso, Jefferson, Larimer, and Weld Counties) and 11 counties are affected in Texas (Bastrop, Falls, Guadalupe, Hidalgo, Jim Wells, Kinney, Nueces, San Patricio, Travis, Val Verde, and Williamson Counties).

Eight premises in Texas (one in Kinney County, two in Nueces County, two in San Patricio County, two in Hidalgo County, and one in Jim Wells County) have been released from quarantine and 19 other premises in Texas and 42 in Colorado are on a 21-day countdown to quarantine release.

Also of major concern is the number of cumulative susceptible animals in the two states. In an Aug. 13 weekly VS update, USDA-APHIS reported 2,051 animals listed as "at risk" for exposure in Colorado and 2,603 animals in Texas at the current time.

Cumulative susceptible species counts include all positive cases.

Hensley says while the numbers appear startling, they still remain less than similar outbreaks across the Southwest in past years, and the virus is considered a mild animal illness in most cases. Generally, infected animals will recover in a short period of time.

Symptoms

VS is a viral disease which primarily affects horses, cattle, and swine. The agent that causes vesicular stomatitis, VSV, has a wide host range and can occasionally infect sheep and goats. In affected livestock, VSV causes blister-like lesions to form in the mouth and on the dental pad, tongue, lips, nostrils, hooves, and teats.

These blisters swell and break, leaving raw tissue that is so painful that infected animals generally refuse to eat and drink and show signs of lameness. Severe weight loss usually follows, and in dairy cows a severe drop in milk production commonly occurs. Affected dairy cattle can appear to be normal and will continue to eat about half of their feed intake.

Check here for a list of states that require specific documentation for the shipment of horses and livestock across state lines.