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DALLAS Dallas County was the center of the country's West Nile outbreak last year. Within the county, the area around White Rock Lake and North Dallas south of LBJ Freeway to Interstate 35E are the hot spots for the virus, according to new research.

"Just the simple fact that we seem to have identified these areas that seem to be hit harder during outbreaks is useful," said Dallas County Health and Human Services epidemiologist Dr. Wendy Chung, "And we can go ahead and target those areas, perhaps, with more intensive education efforts and prevention efforts, and control efforts."

Dr. Chung helped lead an in-depth study about the unprecedented West Nile virus outbreak of 2012. The research found several factors that can predict and prevent a future health crisis.

Conditions in 2006 and 2012 created a "perfect storm" for a West Nile epidemic. Last year, 19 people in Dallas County died of West Nile virus and hundreds more tested positive for infection, including meningitis, encephalitis and West Nile fever.

The findings are printed in the Journal of the American Medical Association.

"In 2006 and 2012, those two outbreak years were associated with winters that were unusually warm, so very few temperatures below 28 degrees Fahrenheit," Dr. Chung explained. "We also found those outbreak years were distinguished by springs that had unusually large amounts of precipitation and warm summers."

West Nile activity in mosquitoes has a direct impact on human cases. Experts call it the "vector index."

"Infection rates of mosquitoes can very well predict subsequent onset of large numbers of human cases, and we did find that with our study," Dr. Chung said.

The report concludes that early surveillance for infection could provide up to two weeks' advance notice to take aggressive preventive action, including aerial spraying.

Others who have contributed to the study include: Christen Buseman, Sibeso Joyner, Sonya Hughes, Thomas Fomby, Dr. James Luby, and Dr. Robert Haley.

2013 has many of the same environmental factors, except Dallas County reports a huge surge in the abundance of Culex quinquefasciatus mosquitoes, the variety that carries West Nile.

Experts speculate that birds that didn't die off from West Nile infection last year may be immune to the virus this season, and therefore unable to transmit the virus to mosquitoes. Mosquitoes are responsible for passing the infection on to humans.

So far this year in North Texas, only one case of West Nile virus has been confirmed; that case was in Tarrant County.

E-mail jstjames@wfaa.com

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