Three Equine Diseases to Watch For

Foreign horse diseases are being reported in the United States

Diseases can be transmitted by contact, insects, and shared medical equipment.

The summer is shaping up to be an active one with horse enthusiasts enjoying shows, competitions and pleasure riding during the long days and warm temperatures. However, the summer is also being plagued by the increased reported prevalence of three important equine diseases. Prevention is key, so being on the lookout for risk factors while you play with your horse this summer can help you reduce risk of exposure and infection.

Equine Piroplasmosis

Equine Piroplasmosis (EP) is a blood-borne protozoan infection transmitted by ticks or by use of one hypodermic needle between many animals. Once infected, horses can take 7 to 22 days to show signs of illness. EP-infected animals can develop fever, anemia, weakness, lack of appetite, yellowing of the membranes in the eyes and mouth, swollen abdomens, labored breathing, and dark brown to red-tinged urine. Equine Piroplasmosis can also cause equine to have roughened hair coats, constipation, and colic.

Some animals may die from the disease, while others never get sick. Horses with persistent EP infections are carriers of the parasites that cause the disease and are potential sources of infection to other horses. Equine Piroplasmosis is present in South and Central America, the Caribbean (including Puerto Rico), Africa, the Middle East, and Eastern and Southern Europe. Only the United States, Canada, Australia, Japan, England and Ireland are not considered to be endemic areas.

The greatest risk for introduction of this disease is through trading of animals or international equestrian sports, where infected and non-infected animals are in contact. Many disease free countries have the climate suitable for a foreign tick vector, or have ticks which could act as vectors.

In addition to horses, EP can also infect donkeys, mules, and zebras.

Recent reports of Equine Piroplasmosis have come from California.

Equine Infectious Anemia

Equine Infectious Anemia (EIA) is a viral disease of horses, mules, donkeys and zebras that is sometimes fatal. In about 95% of cases, however, the virus does not kill the host, but instead makes the host a life-long carrier. Although most cases only present as occasional fever lasting 24 hours, more severely affected horses can become weak, depressed and unwilling to eat, with additional signs that may include jaundice, increased breathing and heart rate, edema on the abdominal midline, and blood-stained feces. Anemia can but does not always occur, although it is more likely to be severe in chronically infected animals.

Although other insects, including stable flies, can transmit EIA, the most effective vectors are biting flies, such as horse flies and deer flies. The bites of these flies are painful, and the animal’s reaction interrupts feeding. The fly attempts to resume feeding immediately, either on the same animal or on another nearby host, resulting in the transfer of infectious blood. 

EIA survives for a limited time on the mouth parts of insects, and it is less likely to be spread to more distant hosts. This virus can also be transmitted in blood transfusions or on contaminated needles, surgical instruments and teeth floats. It is reported to persist for up to 96 hours on hypodermic needles. EIA may also be passed from a mare to her foal in utero.

This disease is monitored by the Coggins Test, which is required by most states for interstate horse transport. The test determines if antibodies for EIA are present in the horse’s serum. Although the test is an added cost for horse owners, it helps to keep the horse population safe by identifying and stopping shipment of infected horses.

Vesicular Stomatitis

Vesicular stomatitis (VS) is a virus caused disease that primarily affects cattle, horses, and swine. The disease can also affect many other species of animals and has occurred in sheep, goats, wildlife, and occasionally humans. The major significance of the disease is its nearly identical appearance to the truly devastating foot and mouth disease, which was eradicated from the United States nearly seven decades ago.

VS causes vesicles (blisters) that form in the mouth (on the tongue, dental pad and lips), in the nostrils, on areas around the hooves and on the teats. These vesicles swell and break exposing raw tissue. The first noticeable sign is usually excessive salivation due to the vesicles in the mouth. Animals may refuse to eat or drink and may show signs of lameness. Affected animals usually recover within two weeks, but not before losing large amounts of weight due to the intense pain caused by the blisters.

Biting insects and animal-to-animal contact may spread the disease. An infected animal’s saliva and fluid from ruptured vesicles can contaminate feed and water, further spreading the disease.

To determine if any cases of VS have been confirmed in your area, see the USDA Weekly Situation Report.

All three of these diseases are considered to be foreign/exotic diseases and our government has taken significant steps over the decades to eradicate and keep our country free of them. None of them have effective treatments available in the United States (although Equine Piroplasmosis can be treated with special medications). No vaccines are available either. Therefore, avoiding them is best!

If you see any signs in your horse that resemble a possibility of any of these diseases, contact your veterinarian immediately. To help do your part in fighting the spread, read our article on biosecurity and/or download this PDF filled with some great Biosecurity tips to reduce exposure risk. Remember, prevention is our goal!