Michigan’s State Veterinarian Dr. Steve Halstead today announced five cases of mosquito-borne illness in horses, and urged residents to take precautions that include preventing mosquito exposure during late summer outdoor activities and vaccinating horses.

Two horses have tested positive for West Nile virus (WNV), a 7-year-old mare from Kent County and a 5-year-old stallion from Sanilac County. Both are currently under veterinary care. Two other horses were diagnosed with Eastern Equine Encephalitis (EEE). Both came from separate farms in Kent County, and a third suspect horse from Kent County is being tested for EEE at the Michigan State University Diagnostic Center for Population and Animal Health.

Michigan typically sees an increase in the number of cases of West Nile virus and Eastern Equine Encephalitis this time of year, as the virus, which has been circulating in mosquito and bird populations throughout the spring and early summer, gradually spills over to horses, and potentially humans, said Halstead. It is imperative that precautions are taken to prevent exposure to mosquitoes, and it is not too late to vaccinate horses against these diseases to protect them during the remainder of this season.

EEE, commonly called sleeping sickness, and WNV are both caused by specific viruses found in wild birds. Mosquitoes that have fed on birds carrying the EEE or WNV virus can transmit the disease to horses and humans. Some birds are able to harbor the WNV or EEE viruses without becoming acutely ill, thereby serving as reservoirs for the diseases. Horses do not develop high enough levels of the EEE or WNV viruses in their blood to be contagious to other animals or humans.

Horses are dead-end hosts for West Nile virus and EEE, meaning the disease can’t be directly transmitted from infected horses to other horses or humans, added Halstead.

The Michigan Department of Community Health has reported six cases of WNV in humans across the state. Rates of infection in birds and mosquitoes submitted for surveillance purposes have increased in the last two weeks, indicating an increased level of virus present in the state.

Tips for preventing mosquito-borne sickness in horses include:

• Vaccinate your horses. Inexpensive vaccines for EEE and WNV are readily available. It is not too late to vaccinate horses this season. Talk to your veterinarian for details.
  
  
• Use approved insect repellants to protect horses.
  
  
• If possible, put horses in stables, stalls or barns during the prime mosquito exposure hours of dusk and dawn.
  
  
• Eliminate standing water, and drain troughs and buckets at least two times a week.

For more information about WNV or EEE in horses, contact the Michigan Department of Agriculture, Animal Industry Division, at 517/373-1077, or visit www.michigan.gov/mda. For information on human WNV cases and tips for reducing the risk of becoming infected, contact your local health department or visit the Michigan Department of Community Health Web site at www.michigan.gov/emergingdiseases.