State officials urge precautions against mosquitoes due to detection in Marshall County of rare virus

State public health and animal health officials are urging northern Indiana residents to protect themselves from mosquito bites and to monitor their horses for illness in response to the detection of Eastern equine encephalitis (EEE) virus activity in multiple northern Indiana counties.

“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.”

As of August, one horse in Marshall County and several horses in the surrounding counties have tested positive for EEE virus in 2024. No human EEE virus disease cases or infected mosquitoes have been reported in Indiana so far this year. Because suitable habitat for the vector mosquitoes is found throughout the area, humans and horses in all northern Indiana counties are potentially at risk. While the risk of EEE virus infection begins to decrease when evening and overnight temperatures drop to 60°F, the risk is not eliminated until the first overnight hard freeze (32°F).

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

While rare, EEE virus can cause serious illness and has a fatality rate of around 33 percent or higher. Many people who recover may still experience 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 encephalitis (inflammation of the brain). People who are younger than 15 years and older than 50 years are at the greatest risk of severe disease if infected with EEE virus. People who think they may have EEE virus should contact their healthcare provider.

EEE in horses is often called “sleeping sickness” because infected animals become comatose. Other clinical signs may include listlessness, high fever, head pressing, and seizures. Horses that develop EEE rarely survive. Infected mosquitoes carry the virus; it does not spread from horse to horse or horse to human. Contact a veterinarian if any of these signs are noticed. Testing is available for EEE.

To view EEE surveillance data, go to https://gis.in.gov/apps/ISDH/Arbo/. To learn more about EEE virus, visit the Indiana Department of Health website at https://www.in.gov/isdh/28258.htm.

For inquiries related to human health, contact media@isdh.in.gov