INDIANAPOLIS — State health officials are warning people about a rare mosquito-borne virus that kills around a third of those infected.

Often called “sleeping sickness” in horses, the Eastern equine encephalitis (EEE) virus is a rare mosquito-borne virus that can infect both humans and horses. The Indiana Department of Health is alerting people to protect themselves and monitor their horses after confirmed cases in northern Indiana.

As of Oct. 4, two horses in LaGrange County and one horse in Kosciusko County have tested positive for EEE virus in 2022. So far, the department says no human cases have been reported for the year.

“EEE (‘triple E’) virus is a serious threat to both horses and people in northern Indiana,” said Dr. Bret Marsh, DVM, state veterinarian at the Indiana State Board of Animal Health. “While this risk is currently decreasing due to cooler weather, it will persist until the first hard freeze of the year.”

While no human cases have been reported this year, the virus can cause serious illness, with a fatality rate of around 33 percent or higher. Even if people recover, they may suffer long-term complications.

Symptoms of EEE virus disease include chills, fever, body aches and joint pain. Some people develop a more severe form of the disease affecting the nervous system and causing inflammation of the brain.

In horses, the virus causes listlessness, high fever, head pressing and seizures. It is called “sleeping sickness” because infected animals become comatose. Horses that develop EEE rarely survive.

While the risk of EEE virus infection begins to decrease when evening and overnight temperatures drop to 60°F, the department says the risk is not eliminated until the first overnight hard freeze. State officials recommend the following preventive measures for those at risk:

  • Avoid being outdoors when mosquitoes are active (especially late afternoon, dusk to dawn, and early morning)
  • Use an EPA-registered insect repellent containing DEET, picaridin, IR3535, oil of lemon eucalyptus, or 2-undecanone on clothes and exposed skin
  • Cover exposed skin by wearing a hat, long sleeves and long pants in places where mosquitoes are especially active, such as wooded areas
  • Install or repair screens on windows and doors to keep mosquitoes out of your home
  • Vaccinate horses for EEE annually according to guidelines from the American Association of Equine Practitioners

You can eliminate mosquito breeding sites from your property by doing the following:

  • Discard old tires, tin cans, ceramic pots or other containers that can hold water
  • Repair failed septic systems
  • Drill holes in the bottom of recycling containers left outdoors
  • Keep grass cut short and shrubbery trimmed
  • Clean clogged roof gutters, particularly if leaves tend to plug up the drains
  • Frequently replace the water in pet bowls
  • Flush ornamental fountains and birdbaths periodically
  • Aerate ornamental pools, or stock them with predatory fish