The Associated Press

ATLANTA - Health officials on alert for the return of West Nile virus are concerned about the re-emergence of another mosquito-borne disease in the Southeast: eastern equine encephalitis.

A Georgia man died June 21 in the nation's first human case of the disease this year.

Florida, Georgia, North Carolina and South Carolina have seen the highest number of horse cases of eastern equine encephalitis in years.

The disease, which has existed in the United States for decades, kills nearly all unvaccinated horses.

"It's kind of going up the coast," said Laurel Garrison, epidemiologist for the Georgia Division of Public Health.

Although it rarely affects people, it can be more deadly than West Nile. Since 1964, there have been only 153 confirmed human cases of the disease.

"Eastern equine encephalitis has been an exceptionally infrequent disease," said Dr. Anthony Marfin of the Centers for Disease Control and Prevention.

"If you saw five or six (human) cases a year, that was a big year."

But the virus kills up to 50 percent of people who catch it, compared with up to 15 percent for West Nile.

"It's such a serious disease that we've been sending press releases to warn people against this virus," said Nolan Newton of the North Carolina Department of Environment and Natural Resources. "I see no reason why it shouldn't just keep on going up the East Coast."

Florida has had 99 horse cases in 31 counties this year. The virus was confirmed in 11 Georgia horses and two birds. North Carolina has had four horses test positive and South Carolina 17 horse cases.

Virginia hasn't had any, but officials have sent e-mail warnings across the state. It's been detected in a pair of birds in West Virginia and has been found in Mississippi horses and even emus in Alabama.

"We sort of should have expected it," said Dr. Venaye Reece, equine programs coordinator with Clemson University's livestock and poultry health programs office. "It's a cyclic disease and runs in 10-year cycles."

Concern over West Nile - and recently improved detection methods for that virus - may have led to better detection of eastern equine encephalitis, Marfin said.

"If you're collecting mosquitoes and are testing them for (West Nile) virus, you might as well test them for St. Louis encephalitis," Marfin said. "It's raised awareness for mosquito-borne viruses everywhere."

Health officials urge people to use similar precautions against eastern equine as they would against West Nile.

They urge people to wear protective clothing and use insect repellent while outdoors and to get rid of mosquito habitats, such as standing water, around the home.

Horses should also be vaccinated against both diseases.