By Dana N. Zimmel, DVM, Diplomate ACVIM, ABVP (Equine Practice)
Vesicular Stomatitic (VS) is a viral disease that occurs in the Southwest commonly affecting horses, cattle and pigs but can affect sheep, goats and wild animals. The major concern with this disease is that it mimics Foot and Mouth Disease (FMD), which has been eradicated in the United States since 1929. Introduction of FMD into the U.S. would have tremendous economic consequences so the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) monitors any disease that can look similar to FMD. The only way to distinguish VS from FMD in livestock is through laboratory tests. Horses are not affected by FMD.
The clinical signs of VS in horses include fever and blisters on the tongue, lips and coronary bands. The blisters are so painful that the horse may refuse to eat, develop excessive salivation or become lame if the coronary band is affected. The incubation period ranges from 2 to 21 days.
How VS spreads is not fully understood but it is believed to be transmitted by arthropods such as flies, mosquitoes and midges. Horses can spread the virus if the saliva from the ruptured blisters contaminates common areas such as water and feed buckets. The morbidity rate (the risk that an animal will become sick from a disease) is variable and can be as high as 90 percent in a herd. The mortality rate (the risk that an animal will die from a disease) for VS is low for horses. Affected horses may take seven to 14 days to recover and can suffer weight loss from the inability to eat well. Humans can contract the virus if they come into contact with horses that are affected. The clinical symptoms in humans are similar to influenza; fever, muscle aches, headaches and malaise. People should follow proper biosafety methods when handling infected horses.
Controlling an Outbreak
There is not a specific cure for the disease. If a horse has symptoms consistent with the disease the veterinarian must contact the State Veterinarian or the USDA:APHIS immediately. At that time, a blood sample and an oral swab are collected from each suspect animal and the premises are quarantined pending laboratory confirmation of the disease. Farms that have confirmed cases of VS are quarantined for 30 days after all clinical signs have resolved. All sick horses should be isolated from the healthy horses. When working on infected horses, protective latex gloves should be used. Make sure to implement good vector control on the farm.
Differential diagnosis for oral blisters in the horse
· Blister beetle toxicosis
· Chemical stomatitis
· Periodontal gingivitis
· Phenylbutazone toxicity
· Plant awn stomatitis or foreign body
· Yellow bristle grass ulcers
Impact on the Equine Industry
Outbreaks of VS in 1995 involved 365 ranches in New Mexico, Colorado, Arizona, Utah and Texas. In 1997, a similar outbreak of VS was detected on 380 ranches in Arizona, Colorado, New Mexico and Utah. These outbreaks have caused significant economic hardships for the horse industry due to the mandatory restrictions imposed on livestock travel at the local, state, national and international levels. The inability to ship horses to and from these states can result in lost revenue for the breeding, showing, racing and sales industry.
For more information regarding Vesicular Stomatitis, here are some additional resources:
Federal Veterinary Services Offices & Veterinarians (AVIC) http://www.aphis.usda.gov/vs/area_offices.htm
State Resources for Vesicular Stomatitis Information http://www.aphis.usda.gov/vs/ceah/ncahs/nsu/surveillance/vsv//vsv_stateinfo.htm
Reviewed and updated by Amanda House, DVM, DACVIM in 2016.