11/09/2001 12:00AM

A disease that spreads steadily

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LEXINGTON, Ky. - West Nile virus, a mosquito-borne disease that can cause fatal swelling of the spinal cord and brain, was first detected in the Western Hemisphere in 1999 in New York.

Since the first case, the disease has spread steadily in the United States, with the westernmost infection reported in Louisiana. The first case in Kentucky was detected in late August in a Quarter Horse in Bourbon County north of Lexington. That case, the only other reported incidence of West Nile in the state, was not fatal.

This year, the virus has infected at least seven people and resulted in the death of at least one person in the United States. It also has infected 347 horses through Oct. 31 this year, according to the United States Department of Agriculture, which tracks equine cases of West Nile. At least 59 of the horses affected this year, or 23 percent, died or were euthanized because of the disease. The vast majority of the equine cases have occurred in Florida, which has reported 252 equine cases and 31 deaths.

West Nile virus was initially identified in Uganda in 1937. The disease is not contagious from horse to horse or from horse to human. The common house mosquito Culex pipiens carries the virus, which it acquires from feeding on infected birds. The mosquitoes then infect horses or humans by biting them. Infected horses' symptoms can include fever, listlessness, hind-end weakness, lack of coordination, convulsions, inability to swallow, and head-tilting or pressing of the head against walls.

This summer, Fort Dodge Animal Health received a conditional one-year license to distribute an equine vaccine for West Nile. The vaccine, available through veterinarians, requires two doses given about two weeks apart. Vaccinated horses will temporarily test positive for antibodies for the virus.

Public health authorities and the USDA recommend an aggressive mosquito-control program as the first important step in protecting the human and equine population. The USDA's Animal and Plant Health Inspection Service notes that mosquitoes can breed in any puddle that lasts longer than four days, and the service recommends elimination of all such standing water. USDA guidelines also suggest that horsemen clean water troughs thoroughly at least once a month; dispose of or drill holes in the bottoms of containers that can trap water; and use insect repellents.