Although of low mortality in horses, there is a potential public health problemSome diseases that occur in horses also may occur in food-producing animals and/or people, and, although they are not many, their threat to public health makes them of greater overall concern than some plain, old horses-only conditions.
There is a problem right now in the Southwest with vesicular stomatitis (VS), a viral disease that affects not only horses, but also pigs, cattle, certain wild ruminants, and people. It is a reportable disease, which means when it occurs, the government steps in and helps. I have several thoughts concerning the efficacy of this, but this is a veterinary forum, not a political one, so my editorialization shall end here. I think the chief problem we face right now is with the shipment of horses to and from certain areas, and this restricted movement, while inconvenient, will help control and contain the present outbreak.
Cause and spread
There are several types of the VS virus and all affect horses. The disease does not seem to be spread by contact, but is believed to be transmitted by sandflies and possibly other biting insects. Approximately 90% of the cases occur in August and September and most seem to be associated with moist environments; wetlands or pastures with streams or ponds seem to have a higher incidence.

Clinical signs
Incubation is short, 1-to-3 days. In horses, the main sign is inflammation of the tongue and oral mucosa. Vesicles, ranging from one to three millimeters in diameter, form, coalesce, and then rupture, denuding as much as 50% of the tongue. Severely infected animals may refuse, or be unable, to eat. The denuded area is red and raw and has epithelial strands hanging from its edges. There may be frothy, blood-tinged saliva. Water intake may be greatly increased or reduced, and fever, depression, and excessive salivation are the usual symptoms.
In some cases, the vesicles may also appear on the feet (usually around the coronary band), the prepuce of males, and the mammary glands of females. An infected lactating mare may not allow her foal to nurse.

Diagnosis
The clinical signs are sufficient, but to satisfy epidemiologists, viral isolation, a complement fixation test, or a serum neutralization test are definitive.

Treatment and prevention
Vesicular stomatitis runs its course in 7-to-10 days, and there is no mortality from the disease itself, although supportive therapy (nutrition) may be necessary in more heavily infected animals. There is always the possibility of secondary bacterial infection of the ruptured vesicles, so antibiotic therapy should be consideredsystemic for the mouth and tongue and topical for the external areas.
Prevention is tough, especially as it may occur in a wild population near your horses grazing areas. Insect control is your best bet.
Because it is a reportable disease, infected horses must be quarantined. Strict isolation and sanitation procedures must be implemented. It is a pain and an inconvenience, but it is the only way to properly control what could end up as a disastrous disease to food animal-producing farmers and ranchers.