If you haven’t already heard or read about it, Vesicular Stomatitis has started infecting horses in the southwest United States again after six years without any cases. There have been cases on nine ranches in Texas, four farms in New Mexico, and two in Colorado (as of July 16, 2004). The first cases started in Texas at the end of May.

Vesicular Stomatitis(VS) is a viral disease that is thought to be spread by insects (flies, mosquitoes, ticks, etc.) and direct contact or mechanical transmission (tack, buckets, water tanks, etc). Clinical signs of VS include blister-like lesions or erosions on the tongue, in the mouth or nose, and excessive salivation. Some horses may also have lesions on the coronary band of the hoof. The incubation period of VS is usually two to four days. Horses, cattle, and pigs are susceptible to the infection.

Farms that have VS positive animals are required to be quarantined for a period of 30 days following the complete healing of VS lesions on the affected animals. The lesions generally heal in two to three weeks. Prior to lifting the quarantine, the animals must be examined by state or federal regulatory veterinarian.
One of the main reasons that this disease is so highly regulated is that it can look almost identical to Foot and Mouth Disease (FMD). Although horses are not susceptible to FMD, cattle, sheep, and swine are, and the consequences are terrible. FMD is extremely dangerous, highly contagious, and cannot be differentiated from VS without laboratory tests. A VS or FMD outbreak would result in a huge economic loss to the US agricultural community.

Luckily there are many obstacles that are put into place during a VS outbreak to limit the spread of the disease. We talked about the quarantine system. Any suspect cases are to be reported to the state and federal veterinarians for inspection. Kentucky and Florida have imposed restrictions on animals coming from Texas and surrounding states. Animals from 60 West Texas counties and all of New Mexico are prohibited from entering Kentucky or Florida. Also livestock entering both states from the rest of Texas or surrounding states such as Oklahoma, Colorado, Louisiana, Arizona, Arkansas, and Utah must have a negative C-Elisa VS (which is a blood test for VS) test 10 days prior to entry. Horses traveling to the European Union must have a negative virus neutralization test for VS.
Of big concern right now is the World Thoroughbred Championships Breeders’ Cup, which is in Texas this year. Horses from all over the US, Canada, and Europe will be there. The Breeders’ Cup will organize a “disease-free” zone around Lone Star Park in the Dallas-Fort Worth area to bring horses in and out. Already more than 1,400 horses have been tested at Lone Star Park and found to be disease free.

Here in the Northwest, travel across the Canadian border is monitored closely. Health certificates for horses going to Canada must have a statement declaring that they did not come from a VS positive state. If they have come from Texas, New Mexico, or Colorado, they must first be quarantined for 21 days and examined by an accredited veterinarian.
Control of VS like many other arthropod-spread diseases involves control of the insects. Keeping stalls clean and using fly and mosquito control is of primary importance along with disinfecting grooming supplies, buckets, and other equipment between horses. You should bring any questionable lesions or sores in your horse’s mouth to the attention of your veterinarian. There are certainly other diseases that can result in similar clinical signs (i.e. toxic plants, chemical irritants, dental disease, etc).
When traveling, especially to affected states or out of the country, it is wise to call ahead of time to find out what may be required along with your health certificate to enter that state or country. Also expect inspection delays when traveling in the southwest United States. Six years ago, during the last VS outbreak, California required inspections at the border. More information and updated reports can be found at the USDA-APHIS website or at www.TheHorse.com.