Why is West Nile so bad this year?

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by JANET ST. JAMES

WFAA

Posted on July 25, 2012 at 7:46 AM

DALLAS — Mosquito traps from every cesspool and stagnant stream are brought back to the Dallas County mosquito lab, where scientists are on the lookout for West Nile virus.

"There is a high infection rate in our mosquitoes this season," said Dallas County entomologist Scott Sawlis.

Last year, he said few mosquitoes tested positive. This year, from their count, more than half are infected.

This could be the worst West Nile season ever in North Texas. Already, more than 80 human cases have been reported in Dallas and Tarrant counties, and two have turned deadly.

Compare that to 27 cases on record for the entire state of Texas last year.

Dallas County's mosquito surveillance program played an important role in identifying the disease in North Texas unseasonably early. But scientists haven't figured out why it's so bad this year.

"The disease is cyclical, so we've gone the last few years without seeing a lot of activity," Sawlis explained. "But it has to do with environmental factors of what is the population of mosquitoes, what is the weather pattern, bird populations."

A mild winter — along with a healthy bird population that transfers West Nile to feeding mosquitoes — has boosted the insect's population. The more infected mosquitoes there are, the greater potential for biting and infecting a person.

"A year or two ago, if you'd asked me about West Nile, I'd say it's really not an issue anymore," said Baylor Dallas infectious disease specialist Dr. Cedric Spak.

But he is currently treating several hospitalized patients, and is concerned about this sudden epidemic.

"We would like to be able to prevent it, but we don't know how," Dr. Spak said.

He and other area doctors and scientists are gathering data that could help reduce infection in the future. But all agree the key is within the mosquitoes — suddenly buzzing with a lot more disease this year.

Experts say until they have answers, people must protect themselves from this potentially dangerous virus.

Use bug spray from dusk on when mosquitoes are active; wear long sleeves; and dump standing water from the yard.

E-mail jstjames@wfaa.com

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