Equine Reportable Diseases in Michigan, including EIA, EEE, EHV & WNV


Eastern Equine Encephalitis (EEE)

Eastern Equine Encephalomyelitis, also known as "sleeping sickness," is caused by a virus that attacks the nervous system. Horses, people, birds, and a variety of small mammals can contract this disease from a mosquito bite. Mosquitoes spread the virus among wild birds. These birds serve as a reservoir of infection for other animals and mosquitoes act as the transmission vector to horses and people. The disease is not spread from horse to horse or from a horse to a human. An effective vaccine for horses is available and recommended to protect them from EEE.

Equine Herpesvirus (EHV-1, EHV-4)

Equine Herpesvirus (EHV) is a viral disease of horses and other equidae. The disease can be caused by several different strains, but most commonly type 1 which causes respiratory disease, abortions, and/or neurologic disease, type 3 which causes coital exanthema, a venereal disease resulting in vesicles/pustules on the genital area of both male and female equidae, and type 4 which causes respiratory disease, especially in weanlings, but can rarely cause abortions, too. The neurologic form of type 1, also called Equine Herpesvirus Myeloencephalopathy, and the respiratory form of type 1 and type 4, called Rhinopneumonitis, are reportable in the State of Michigan. EHV is transmitted by direct contact with ill equidae via respiratory or reproductive secretions, but also can be spread indirectly via contact with people, tack, buckets, vehicles, and other items that have had contact with ill animals. The best way to prevent the disease is via vaccination. Biosecurity is also very important. Horses and other equidae entering the premises (new horses and horses returning from events) should be quarantined from resident equidae for 4 weeks. Pregnant equidae should be kept away from young equine as they are the population most likely to become ill with the respiratory form. Ill equidae should be isolated from healthy equidae and either be cared for solely by a designated caretaker or cared for after healthy horses. Individuals caring for ill animals should wear protective gloves, boots, and clothing when caring for those animals to avoid spreading the disease to other equidae. All items in contact with ill animals should be cleaned and disinfected before contact with other equidae.

Equine Infectious Anemia (EIA)

Equine Infectious Anemia (EIA), also known as "swamp fever" and "Coggins Disease," is caused by a virus that attacks red blood cells. Only equine (e.g., horses, ponies, mules, and donkeys species) are affected. Introducing certain body fluids, usually blood, from an infected horse to a healthy horse transmits this disease. This can be accomplished by an insect (typically horse flies or deer flies) or by a variety of mechanical means (such as the repeated use of a single needle on a number of horses, one of which is infected). Rarely, foals may acquire the disease from their mother during gestation.  There are four "patterns" of EIA, and, depending on the pattern, signs of EIA can  include depression, anemia, intermittent fever, depression, and/or severe weight loss, although some animals never show signs. A blood test, known as a coggins test, is performed to detect the disease. There is neither a vaccine to help prevent EIA nor an effective treatment for EIA.  Equine with EIA are infected for life.

  • Michigan law requires horses and other equidae to have tested negative for EIA within the previous 12 months prior to the animal moving in order to do any of the following:
    • Travel to and enter onto the premises of an auction market in Michigan.
    • Enter in publicly held exhibitions, fairs, or shows in Michigan. Publicly held exhibitions include horse shows, races, pulls, parades, team penning events, and similar activities.
    • Be sold in Michigan, if the animal will leave the premises when sold.
    • Be imported into Michigan. An Interstate Certificate of Veterinary Inspection, or health certificate, is also required to import horses and other equidae. Foals 6 months of age or younger and still nursing their mother are exempt from testing requirements, providing the mother has a current negative EIA test. Look here for requirements needed to import horses and other equidae into Michigan.


Strangles is a bacterial disease that can be spread directly through horse contact or indirectly through exposure to things like trailers, equipment, tack, clothing and facility surfaces that may have come into contact with a sick horse.

West Nile Virus (WNV)

West Nile Virus (WNV) is caused by a virus that primarily infects and multiplies in birds, which serve as reservoirs for the virus. The virus is spread between birds through the bite of an infected mosquito. Like EEE, WNV requires a bite from an infected mosquito and cannot be transmitted directly from infected horses to other horses or humans.  Mosquitoes can spread the disease to humans and other animals, including horses. Mosquito precautions for horses are recommended and horses should be annually vaccinated against the disease. Taking steps to prevent standing water where mosquitoes can breed, such as by frequently changing the water in bird baths, planter trays, and animal water bowls/troughs, as well as removing old tires and filling puddles, is also advised.

Contact Information

If you have any further questions on anything listed above, or any reportable equidae disease, please call:
Michigan Department of Agriculture and Rural Development
Animal Industry Division