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Vesicular stomatitis outbreaks detected in horses

Texas becomes third state to confirm viral disease in 2020.

The Texas Animal Health Commission (TAHC) reported that vesicular stomatitis virus (VSV) was confirmed April 23 in horses on two Starr County, Texas, premises.

TAHC said the National Veterinary Services Laboratories (NVSL) confirmed the virus as the New Jersey serotype, and these mark the first cases of VSV in Texas this year.

According to TAHC, the 2020 U.S. outbreak of VSV began April 13, when NVSL confirmed the first VSV-positive premises in New Mexico, with subsequent cases detected in Cochise County, Ariz., and now the Starr County, Texas, premises.

The New Mexico Livestock Board noted that it had detected VSV (Indiana serotype) cases in Dona Ana and Sierra counties. The Arizona Department of Agriculture also indicated its case was of the Indiana serotype.

The horses in Texas were tested after the individual owners observed lesions on the horses’ muzzles and contacted their veterinary practitioners. The animals are being monitored, and the premises will remain under state quarantine until 14 days from the onset of lesions in the last affected animal on the premises, TAHC said.

“VSV is spread by direct contact with infected animals or spread by insect vectors like black flies, sand flies and biting midges,” TAHC executive director Dr. Andy Schwartz said. "The epidemiological investigations on the VSV-positive premises indicate that VSV-infected insects are likely the source of infection on these premises. Biosecurity measures and vector mitigation have been instituted to reduce the spread of the virus."

Vesicular stomatitis is a viral disease that primarily affects horses and cattle and occasionally swine, sheep, goats, llamas and alpacas, TAHC explained. VSV can cause blisters and sores in the mouth and on the tongue, muzzle, teats or hooves of susceptible animals. Additional signs of infection include fever, drooling or frothing at the mouth, reluctance to eat, lameness or laminitis if lesions develop around the coronary band. Lesions usually will heal in two or three weeks, and most animals recover with supportive care by a veterinarian.

VSV prevention

Even with the best defensive measures, VSV still can infect a herd, so TAHC provided the following tips to help protect livestock:

  • Control biting flies (with fly spray, fly traps, maintaining clean pens, etc.).
  • Keep equine animals stalled or under a roof to reduce exposure to flies.
  • Feed and water stock from individual buckets.
  • Don’t visit a ranch that’s under quarantine for VSV. Wait until the animals have healed.
  • Restrict nose-to-nose contact between horses from other premises.
  • Clean and disinfect tack and equipment between uses.

2019 outbreak

Last year, a large VSV outbreak began on June 21, 2019, when NVSL in Ames, Iowa, confirmed the first VSV-positive (Indiana serotype) premises in Kinney County, Texas, according to a follow-up report from the U.S. Department of Agriculture's Animal & Plant Health Inspection Service (APHIS).

Over the summer months, seven other states — New Mexico, Colorado, Wyoming, Oklahoma, Nebraska, Utah and Kansas — subsequently reported NVSL-confirmed cases, APHIS noted.

In total, APHIS said 1,144 VSV-affected premises were identified (672 suspected and 472 confirmed positive) in 2019, with 1,128 of these premises housing only clinically affected equine species, 15 premises housing only affected cattle and one premises housing both affected cattle and horses.

According to APHIS, in 2019:

  • Colorado had the most identified affected premises, at 693 in 38 counties.
  • Texas identified 172 affected premises in 37 counties.
  • Wyoming identified 149 affected premises in 11 counties.
  • New Mexico identified 76 affected premises in 12 counties.
  • Utah identified 26 affected premises in six counties.
  • Nebraska identified 26 affected premises in five counties.
  • Oklahoma identified one affected premises in one county.
  • Kansas identified one affected premises in one county.

All 2019 VSV-infected or suspect premises in all affected states have completed the quarantine period and have been released, APHIS said.

In a fact sheet, APHIS explained that vesicular stomatitis is a reportable disease and is one of several diseases with similar clinical signs. One of those, foot and mouth disease, is a foreign animal disease that would cause devastating economic consequences if it is found in the U.S.

APHIS said the only way to tell these diseases apart is through laboratory testing, so it’s important to test any animal with clinical signs quickly to identify which disease is causing illness.

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