West Nile virus was first documented in the U.S. in 1999. Harbored in birds and transmitted by mosquitoes, it spread quickly across the country. This year Dallas County has had a total of 83 confirmed human cases and three deaths associated with West Nile virus. The virus is particularly harmful to children, the elderly or people with weak immune systems.

In the new study, appearing in this month's issue of the Journal of Virology, Dr. Gale and colleagues compared a virus isolated from an infected bird in Hall County, in the Texas Panhandle, with a milder strain from Madagascar.

The researchers found that the Texas strain can subvert the body's first attempt to limit the virus's replication in the body. Normally, within a few hours after infection, the body's cells are producing interferon, a biochemical trigger for a coordinated immune system attack. But the Texas strain clogs up the interferon response, giving the virus a head start in its spread throughout the body.

By contrast, Dr. Gale and his colleagues found, the Madagascar strain can't clog up the interferon response so the virus is not as damaging.

"People have observed before that the African isolates are less virulent," said Dr. Robert Tesh, a pathologist at the University of Texas Medical Branch at Galveston. "This is an explanation of why."

Scientists have previously proposed that a weak strain of the West Nile virus could be the basis for a vaccine, and the current findings are in line with that notion.

"What we've got here is the footwork for how to design a vaccine," UT Southwestern's Dr. Gale said. "We think the key to a good vaccine will be to produce a mild virus that won't block interferon."

Other candidates for developing a vaccine include the mild Kunjin strain, which circulates in Australia, as well as a variety of genetically engineered viruses.

But developing a vaccine has its challenges, said the NIAID's Dr. Repik.http://www.wfaa.com/sharedcontent/dws/news/localnews/stories/DN-westnile_01nat.ART.State.Edition1.3f433c2.html

West Nile detected in Benton County
Corvallis Gazette Times - 0 KB- Found: 2 hours ago
A dead bird from Corvallis tested positive for West Nile Virus last week, making it the first local case of the year, according to scientists at Oregon State University’s Veterinary Diagnostic Laboratory.