EEE Outbreak in Wisconsin

As many as 30 horses in northwestern Wisconsin recently died from what officials believe is Eastern equine encephalomyelitis (EEE). Most of the cases were found in an area 30 miles north of Eau Claire, Wisc., in Rusk, Chippewwa, Sawyer, and Barron Counties.

Michigan also detected evidence of EEE recently in three Kalamazoo County gray catbirds. This served as a reminder to horse owners to vaccinate their horses against EEE and reduce the population of mosquitoes that spread the disease.

According to Robert Ehlenfeldt, DVM, Wisconsin's Assistant State Veterinarian, EEE was confirmed by virus isolation in one horse by USDA National Veterinary Services Laboratories and the Minnesota Department of Agriculture, and four other horses were serologically positive for EEE. All tested negative for West Nile virus (WNV).

Ehlenfeldt said that none of the clinically affected horses had been vaccinated for EEE, and most were pasture-kept in an area that is considered lowlands or swamp. These conditions, combined with increased rainfall and high temperatures, have created a bumper crop of mosquitoes that readily spread the disease.

"We haven't seen anything like this in the 20 years I've been here, and one of the vets extended that to 29," explained Ehlenfeldt. "(Typically) here in the state office, we get a report of a singleton case (of EEE) every couple of years. You don't hear about encephalitis around here. People get complacent and they forget to vaccinate."

The outbreak has caused a great deal of concern for Wisconsin horse owners, but public health announcements have reminded them that EEE is not a horse-to-horse disease, and described ways owners can reduce horses' exposure to mosquitoes. Officials assure horse owners that the cases didn't look like WNV, Venezuelan equine encephalomyelitis, or Western equine encephalomyelitis.

EEE can be incubated from one to three weeks. "It's been a two- to four-day clinical course," Ehlenfeld said. "In a pasture horse, people might not notice the initial signs. (Veterinarians) usually get a call about a lethargic horse with a little ataxia, droopy eyes and lips, and within one to two days, the horse is down."

Infected horses also can develop fever, inappetence, depression, elevated heart rate, and white blood cell count abnormalities.

Horse owners and veterinarians are advised to vaccinate or booster horses for EEE in the face of this outbreak. At press time, Ehlenfeldt said that the outbreak seemed to be slowing down.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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