Horses

Vesicular stomatitis virus (VSV) causes sores on the mouths or hooves of infected animals. Horses are one of the most severely affected species, although cattle, swine and donkeys can also be affected.

VSV can be transmitted by insects or direct contact with infected animals and contaminated objects. It causes sores in the mouth, nostrils, hooves and teats. The blisters swell and break, leaving raw tissue. Animals often refuse to eat or drink. When blisters occur around the hooves, lameness can occur. Weight loss usually follows, and in dairy cows a severe drop in milk production is often seen.

Since VSV is so similar to foot and mouth disease, it should be reported to the Board of Animal Health. Horse owners can protect their animals by avoiding contact with other horses. Horse owners should also voluntarily quarantine their horses from the rest of their animals when returning from rides or events in an area with known VSV infections.

Humans can become infected with VSV when handling infected animals (direct contact). In affected people, vesicular stomatitis causes a flu-like illness with symptoms of fever, muscle aches, headache and weakness. Rarely, humans can get oral blisters similar to cold sores. Recovery usually occurs in four to seven days.  If symptoms arise, contact your physician and tell them you have been in contact with animals with VSV.

Use protective measures such as gloves and a mask when handling animals suspected of having vesicular stomatitis. When working with animals, good personal hygiene with frequent hand washing is important in controlling most diseases that can spread from animals to humans.

Equine infectious anemia (EIA) is a viral disease of horses most frequently transmitted by large biting flies between horses in close proximity. There is no vaccine or treatment for EIA. Once a horse is infected, it remains infected for life and is always a potential reservoir for spread of the disease.

EIA infected horses must be permanently quarantined and isolated or be euthanized to prevent the disease from spreading to other horses (Minnesota Rules 1721.0260).

Horses must have a negative test for EIA within 12 months prior to importation or attendance at public exhibitions in Minnesota.

Veterinarians can request additional Equine Infectious Anemia laboratory test forms (VS 10-11) from our online federal forms request page.

Equine herpesvirus (EHV) is a contagious virus that can cause four clinical presentations including: neurological disease, respiratory disease, neonatal death and abortion. Equine herpesvirus myeloencephalopathy (EHM) is the neurologic disease that develops as a result of EHV infection. The virus has been associated with neurologic cases in llamas and alpacas, but has no effect on people or other types of livestock.

The virus is usually spread in nasal secretions between horses that are in close contact with each other or that share water or feed pails. The virus does not typically survive very long in the environment or on people or equipment. It is killed readily by most disinfectants, ultraviolet light and by drying. Infected horses are generally treated with supportive care. Anti-inflammatory drugs and antiviral medications are often used for those that develop the neurologic form of the disease.

EHM positive horses and EHM exposed horses must be quarantined as outlined in the Board of Animal Health EHM control plan. Board staff members will then work with herd veterinarians and horse owners to carry out the testing and observation protocols defined in the control plan before the quarantines can be released.

Contagious Equine Metritis (CEM) is a venereal disease of horses caused by a bacterium called Taylorella equigenitalis. CEM may be spread through natural breeding, artificial insemination, and contaminated equipment. Mares infected with CEM may show mild or more severe degrees of uterine inflammation and vulvar discharge. Abortion and permanent infertility can occur. Stallions and mares infected with CEM may not show symptoms, but can carry and spread the disease for years. Infected horses can be successfully treated with antibiotics and disinfectants.

CEM is considered a foreign animal disease, not endemic in the United States. If a horse in Minnesota is infected or exposed to the disease, the Board will place the horse under quarantine. Testing and treatment protocols must then be completed before quarantines can be released.

Eastern and Western Equine Encephalitis (EEE & WEE) and West Nile virus are endemic diseases in the United States. Birds serve as the primary hosts for these diseases. These viruses are transmitted from birds to horses or people through the bite of infected mosquitoes. These viruses can cause encephalitis, an inflammation of the brain and spinal cord. Infected horses may or may not show neurological symptoms and many recover completely from these diseases.

Vaccines for horses are widely available and have been proven to be effective in preventing infection. Steps can also be taken to reduce the risk of these diseases by reducing mosquito populations. Practices such as changing water in drinking troughs every week, mowing long grass, draining stagnant water puddles, and removing items such as old tires and tin cans may help to eliminate mosquito breeding grounds. Horses and people can also be protected from mosquitoes by using repellents and placing screens over windows and stable doors.

Positive test results for equine encephalitis or West Nile virus must be reported to the Board of Animal Health.

High nitrate concentrations in water can harm livestock and domestic animals. Horses and ruminants like cattle, sheep, and goats are most susceptible to nitrates. Bacteria in their digestive systems reduce nitrate to nitrite, and the elevated nitrite levels in the blood can interfere with hemoglobin’s ability to carry oxygen through the body. Symptoms of nitrate poisoning include labored breathing, a blue muzzle, trembling, lack of coordination, and an inability to stand. The effects can be reversed if nitrates are removed from the animals’ diet. Review the Board’s “Guidance on nitrates in livestock water supply” document for information on how to interpret nitrate test levels and take appropriate action.