Common Horse Diseases

Biosecurity – The Key to Keeping Your Horses Healthy (pdf 555kb) – Information for horse owners to reduce the changes of an infectious disease being carried into a farm by people, animals, equipment, or vehicles.

Contagious Equine Metritis – A transmissible, exotic, venereal disease of horses caused by the bacterium Taylorella equigenitalis. Thoroughbred horses appear to be more severely affected by the disease than other breeds. Because animals may be asymptomatic, the disease is difficult to detect and control.

Eastern equine encephalitis (EEE), western equine encephalitis (WEE) and Venezuelan equine encephalitis (VEE) are caused by Alphaviruses. Birds and rodents are the primary reservoirs, but unvaccinated horses are particularly susceptible and often serve as sentinels. These diseases are zoonotic, infecting humans, and are a public health concern. Eastern equine encephalitis is the most common of the three and is found widely in several regions of the United States (especially in areas of high mosquito populations). Western equine encephalitis occurs infrequently, but circulates in wildlife. Venezuelan equine encephalitis is a Foreign Animal Disease and therefore reportable at both the Federal and State level. It occurs in cycles in Central and South America; and there have been incursions into the United States decades ago.

Equine Herpes Virus or Equine Rhinopneumonitis virus or EHV is a highly infectious viral disease. The virus can survive for 14 to 45 days in the environment and is spread via the respiratory tract or from aborted fetuses, membranes and fluid. Infected foals can also pass the infection onto healthy mares in their group via their respiratory systems.

Equine Infectious Anemia – EIA is a viral disease of members of the horse family. The equine infectious anemia virus (EIAV) is categorized as a retrovirus: it contains genetic RNA material, which it uses to produce DNA. This DNA is then incorporated into the genetic makeup of infected cells. Identified in France in 1843 and first tentatively diagnosed in the United States in 1888, EIA has commanded a great deal of attention over the years. There is no vaccine or treatment for the disease. It is often difficult to differentiate from other fever-producing diseases, including anthrax, influenza, and equine encephalitis.

Equine Viral Arteritis (EVA) is caused by arterivirus. Clinical signs include fever, respiratory problems, severe coughing and the accumulation of fluid in the body. The virus is transmitted by secretions from infected animals. Control measures are primarily aimed at stallions because they spread the disease via semen.

Equine Piroplasmosis is a disease of Equidae (horses, donkeys, mules, and zebras), and is caused by two parasitic organisms, Babesia equi and Babesia caballi. Although, Equine Piroplasmosis is primarily transmitted to horses by ticks, this bloodborne disease has been spread mechanically from animal to animal by contaminated needles.

Equine Viral Arteritis (EVA) is a contagious viral disease in horses caused by Equine Arteritis Virus (EAV). Infection can go undetected by horse owners/breeders and in herds that were previously unexposed (naïve) abortion rates in pregnant mares can reach up to 70%. Most horses infected with EAV will show minimal if any clinical signs and recover without incident although stallions can become carriers and lifelong shedders of the virus. There is a vaccine available that has been shown to prevent infection with EAV. Vaccination should be performed at least 21 days prior to the start of breeding season to provide adequate levels of immunity. EVA has not been shown to be zoonotic.

Vesicular Stomatitis is a viral disease characterized by fever, vesicles, and subsequent erosions in the mouth and epithelium on the teats and feet. Horses, cattle, and pigs are naturally susceptible; sheep and goats are rarely affected.

West Nile Virus is spread by infected mosquitoes, and can cause serious, life-altering and even fatal disease. Virus transmission may occur in parts of the country where mosquitoes are still active.

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