Five Horses Test Positive for Eastern Equine Encephalitis in New York

Feeding mosquito engored with blood.
Feeding mosquito engored with blood. PD-USGOV-HHS-CDC

Newsdate: Monday, September 17, 2023 – 11:30 am
Location: CANTON, New York

Several North Country horses have tested positive for eastern equine encephalitis (EEE) this summer. The rare but serious disease is spread by mosquitoes and can cause brain inflammation. Three horses in St. Lawrence County and one each in Franklin and Clinton counties have tested positive. So far, no human cases have been reported in the region or throughout New York state.

Disease progression from bird to mosquito - then to horse and/or human.

Disease progression from bird to mosquito - then to horse and/or human. -

Although New York has seen several triple E cases in horses this year, there haven’t been any human cases, which is fortunate because, unlike for horses, there’s no human vaccine for EEE.
© 2020 by Department of Health New window.

Karen Lassell, the equine manager at the William H. Miner Agricultural Institute in Chazy, said the disease causes horses to have a fever, go off their feed and experience neurologic symptoms like an inability to swallow, loss of balance and tremors. It can also be fatal for them. Ultimately, it is not a treatable disease," she said. "So the only way we can treat for it is to prevent it with vaccination."

Lassell said the Miner Institute vaccinates its horses against triple E every year. "So I’m not terribly afraid of it all the time, but certainly I’m aware of it being local and had been wondering (about it) with the mosquito population being seemingly higher this year than recent years." Lassell said she's spoken with horses' local veterinarian, Palmer Veterinary Clinic in Plattsburgh, and a state Department of Agricultural and Markets veterinarian about the disease.

"There's always a few cases each year; there's definitely been a few more so far," she said, "and they've come further north and east in the States than they have in a long time. So, you know, that's kind of definitely put us on a little bit higher alert."

One of the most recent cases of EEE was a horse in Schuyler Falls who tested positive. Schuyler Falls is in Clinton County, like the Miner Institute in Chazy. But Lassell said she's pretty comfortable with her horses' vaccination status. "Our horses are vaccinated annually and we do it at a time in the spring such that, hopefully, they're hitting peak immunity about when the mosquitoes are really also hitting their peak of the season.

She said the Miner Institute also puts fly spray and bug repellants on its horses when they're outside at certain times. "And then we're always keeping an eye out for any horse that looks like they're behaving a little bit differently because there's other mosquito-borne diseases, too, that can happen this time of year, or other bug diseases. So we'll be watching for if any horse certainly decides not to eat or just seems lethargic or depressed. We're going to jump in really quickly to try to figure out what might be going on."

Lassell said this summer's been warmer and wetter than in previous years, and that's caused an overflow of mosquitoes. "So ... the ability to transfer (EEE) is moving that much farther and faster than normal years." Still, even though New York has seen several triple E cases in horses this year, there haven’t been any human cases. According to the U.S. Centers for Disease Control and Prevention, there’s an average of 11 in the whole country reported each year. So far in 2023, there’ve been six, all in southern states.

Like with horses, triple E can cause a variety of symptoms in humans. But unlike for horses, there’s no human vaccine for EEE. There are also no medications to treat it. Flynn says it is very rare — there’ve only been eight cases in New York state over the last 20 years — but it’s still worth protecting yourself from mosquito bites. Flynn said that includes using insect repellant and covering your skin when you’re outside, but also taking preventive measures around your home.

"Make sure that all the screens in your home on the windows and doors are free of rips, tears, holes, things like that, to keep (mosquitoes) out of your home," she said. "And a really big one — especially this summer because it’s been a very wet summer for us — is eliminating standing water in and around your home. That’s where mosquitoes breed."

Flynn said that includes making sure roof gutters are draining properly and dumping stagnant water in things like spare tires, buckets, planters, kids’ toys and pools, bird baths, flower pots and trash cans once a week. Residents should also clear the vegetation and waste from the edge of their ponds, she said

You can also purchase ... mosquito dunks — they almost look like a donut — if you have places where you know you typically have standing water in and around your home. You can put those in the water to actually kill any of the larvae, the mosquito eggs that are in there so they don’t create more mosquitoes. And then of course you can hire an (insect control) professional to come and take care of your yard itself."

Flynn said EEE is rather rare, but is pretty serious when it does happen. "It’s certainly something that comes up every summer that we want to make sure that we’re aware of. And it’s just really another good reminder that we have those vector-borne diseases in our area, so things that are transmitted by mosquitoes, by ticks."

Flynn said those tick-borne illnesses include Lyme disease and anaplasmosis. She said Clinton County is seeing more human cases of both and part of the reason is climate change. "Now that our winters don’t get as cold, more ticks are surviving through that winter season which means they’re around again in the springtime and they’re a little bit older, a little bit bigger, so we’re seeing an increase in ticks in our area and subsequently tick-borne illnesses." Flynn said mosquito-borne diseases — like EEE — may also increase as warmer fall temperatures extend their season.

Press release by NCPR - Article by Cara Chapman

About the Author

Press Release

Author picture

This news article is a press release received by the organization or person noted above. Press releases from recognized horse health companies and individuals are frequently posted on EquiMed as a service to our visitors. Please contact the author of the press release directly for additional information.