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By Amanda Gardner
HealthDay Reporter

WEDNESDAY, Aug. 22 (HealthDay News) -- This year's West Nile virus outbreak is on track to be the biggest ever since the virus first appeared in the United States in 1999, U.S. health officials reported Wednesday.

As of the third week of August, there have been a total of 1,118 cases of West Nile virus in people in 38 states, including 41 deaths.

"The number of West Nile virus disease cases has risen dramatically in recent weeks, and indicate that we're in the midst of one of the largest outbreaks ever seen in the U.S.," Dr. Lyle Petersen, director of the division of vector-borne infectious diseases at the U.S. Centers for Disease Control and Prevention, said during a noon news conference.

Fifty-six percent of this year's cases have been classified as neuroinvasive diseases, such as encephalitis or meningitis.

In Texas, which has been hardest hit by the epidemic, 586 cases have been reported with 21 deaths, said Dr. David Lakey, commissioner of the Texas Department of State Health Services.

The state reported only 10 deaths in the entire span of time from 2003 through 2011, he noted.

Officials in Dallas County, Texas, began aerial spraying of insecticides overnight last Thursday.

Louisiana, Mississippi and Oklahoma have also been hit hard by West Nile virus this summer.

Experts do not know why this year's outbreak is so much worse than previous years, but suspect it could be a confluence of factors, most notably hot weather.

"Hot weather seems to promote West Nile virus outbreaks," Petersen said. "Hot weather, we know from experiments done in the laboratory, can increase the transmissibility of the virus through mosquitoes and that could be one contributing factor."

The number of birds that are infected and then pass the virus on to mosquitoes probably also plays a role, he added.

The number of neuroinvasive cases this year is larger than seen previously, though it's not clear if this is simply because of the way cases are reported or if there is an actual increase in these more severe infections.

Generally speaking, 80 percent of people who are infected with West Nile virus develop no or few symptoms, while 20 percent develop mild symptoms such as headache, joint pain, fever, skin rash and swollen lymph glands.

Less than 1 percent will develop neurological illnesses, such as encephalitis or meningitis, and develop paralysis or cognitive difficulties that can last for years, if not for life.

There are no specific treatments for West Nile virus; the greatest risk for infection with West Nile virus typically occurs from June through September, with cases peaking in mid-August.

And because reporting lags behind actual infections, "we expect many more cases to occur and the risk of West Nile infection will probably continue through the end of September," said Petersen.

Although most people with mild cases of West Nile virus will recover on their own, the CDC recommends that anyone who develops symptoms should see their doctor right away. The best way to protect yourself from West Nile virus is to avoid getting bitten by mosquitoes, which can pick up the disease from infected birds. The CDC recommends the following steps to protect yourself:

• Use insect repellents when outside.
• Wear long sleeves and pants from dawn to dusk.
• Don't leave standing water outside in open containers, such as flowerpots, buckets and kiddie pools.
• Install or repair windows and door screens.
• Use air conditioning when possible.

More information

The U.S. National Library of Medicine has more information on West Nile virus.

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