Dallas Declares State of Emergency to Fight West Nile Outbreak

As West Nile infections top 300, Dallas defies controversy, will begin aerial spraying of pesticides.

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The mayor of Dallas declared a state of emergency in the city as West Nile virus cases continue to climb. The hundreds of cases provoked the city to begin aerial spraying of mosquito pesticides to stop the virus's spread.

Three counties in the Dallas metro area, at 6.5 million the nation's fourth-largest, have reported more than 300 cases and 12 deaths. Statewide, there have been 465 cases and 17 deaths this year, according to the Texas State Health Department.

Mayor Mike Rawlings's move to spray pesticide has been seen as controversial, but he has stood by it.

"I want to take the politics out of it, I want to say this is my responsibility," he told CBS News. "I'll take the heat for it."

Barring rain or weather interference, the spraying will begin tonight. Two small, twin-engine planes flying at 300 feet will conduct the sprays. Though the pesticide breaks down in water and sunlight, public health officials have recommended that Dallas citizens cover sensitive fish ponds and wash fruits and vegetables thoroughly as precautionary measures.

According to the Centers for Disease Control, the 693 cases of the virus reported in the U.S. in 2012 is the highest number reported at this point of the year since the virus was discovered in the U.S. in 1999. The vast majority of the cases have occurred in three areas: South Dakota, the west coast of California, and the Gulf Coast states such Texas, Mississippi, and Louisiana. Texas accounts for nearly half of the nation's cases this year.

It's unclear why the Dallas area has hundreds more cases of the virus than the rest of Texas, including equally large Houston, which has had less than 10 cases.

"All the science isn't perfectly mapped out yet," says Carrie Williams, director of media relations at Texas's state health department. "The short answer is we don't fully understand why."

Some environmental conditions increase its likelihood, such as standing water and the number of virus-carrying mosquitos. Beyond that, the CDC's guidance is only to wear insect repellent with DEET, sleeves that cover exposed skin, and ensure screens are placed on windows, says Lola Russell, a spokeswoman for the agency.

The mosquito-borne virus causes symptoms in approximately 20 percent of those infected. Those symptoms, such as fever and head and body aches, are mild compared to the symptoms of those affected by a harsher, neuroinvasive form of the virus. This severe infection can cause paralysis, stupor, tremors, and muscle weakness, but affects only about 1 in 150 of those infected.

There is currently no specific treatment or vaccine for the virus.

Seth Cline is a reporter with U.S. News and World Report. Contact him at scline@usnews.com or follow him on Twitter.