Worst West Nile Outbreak in U.S. History is Waning

This year's outbreak of cases of the West Nile virus (WNV) was the worst in U.S. history, but the CDC says it may be waning, according to an article on WebMD. Cases in the second week in September were up 35% from the week before. But instances of the disease, which is spread by mosquitoes, are expected to decline as the weather cools in much of the nation and the insects die off.

West Nile virus activity by state as of Sept. 18th, via CDC.

WNV is spread by mosquitoes that feed on birds that are infected with the virus. Mosquitoes can not spread WNV from one person to another.

Cases of WNV have been seen in 48 of the 50 states, and through Sept. 18th 3,142 cases of human West Nile virus disease have been reported to the CDC, with 134 deaths.

The good news is that about 80% of the people who are infected with WNV won't show any symptoms at all. The 20% that do exhibit symptoms will suffer from maladies such as:

• fever
• head and body aches
• nausea and vomiting 

People may also experience swollen lymph glands or a rash on the body.

Only one in 150 people who become infected with WNV experience severe symptoms. Of the U.S. WNV cases reported, 52% "were classified as neuroinvasive disease (such as meningitis or encephalitis)," while 48% involved non-neuroinvasive disease. The severe symptoms may include "high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis."

Encephalitis is swelling of the brain; meningitis is swelling of the tissues that cover the brain and spinal cord.

While few people will develop the severe forms of WNV, the symptoms above shouldn't be taken lightly. As the CDC notes, these symptoms "may last for several weeks, and neurological effects may be permanent."

For more information on West Nile virus:

• CDC page on preventing mosquito bites
• CDC's West Nile virus homepage, where you can find a West Nile fact sheet, data and maps on the 2012 outbreak, and tips on how to choose a mosquito repellant
• WebMD special report on West Nile virus

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