people, but about one in every 150 develop serious illness, that can include high fever, coma, seizures and encephalitis and meningitis. Children, the elderly or people with weak immune systems are most at risk.

There is no vaccine. Doctors can only treat symptoms of the disease.

Searching for clues that might allow development of a vaccine, Dr. Gale and his research team compared one strain from each of West Nile's two basic categories: the harmful strains associated with outbreaks of encephalitis and meningitis in North America, and non-harmful strains from Madagascar and Cyprus.

They studied a harmful strain isolated from an infected grackle from Hall County, Texas, in 2002, and a harmless strain isolated from an infected parrot from Madagascar in 1978.

They mapped the genetic makeup of each strain, and thenhow the strains block signaling, a project Dr. Gale's team is already at work on.

Fortunately, North American strains are extremely similar - in fact, the one that appeared in the United States in 1999 and the Texas strain used in this study are 99 percent identical. One vaccine could, in theory, prevent illness from many of the harmful strains, Dr. Gale said.

"We feel a vaccine could be highly effective in preventing infection," said Dr. Gale.
Dr. Brenda Fredericksen of UT Southwestern and researchers from the Washington University School of Medicine, Texas Veterinary Medical Diagnostic Laboratory and UT Medical Branch in Galveston also were involved in the study.

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