West Nile cases through Oct. most in US since 2003

An outbreak of the West Nile Virus in North Texas has prompted the first aerial pesticide spraying in the area since the 1960's. Manuel Bojorquez reports.

Newly-released West Nile Virus data suggests 2012 may be shaping up to be one of the worst years for the virus in United States history.

The Centers for Disease Control and Prevention announced there have been 3,969 cases of West Nile virus disease in people, including 163 deaths as of October 2, 2012. It is the most cases reported through the first week in October since 2003.

In 2003, nearly 9,900 people became infected with West Nile virus and 264 people died, according to the CDC.

A CDC spokesperson told CBSNews.com it's hard to predict how many more viruses will be identified through the end of the year. The disease typically peaks in late August so the worst of the current outbreak may have passed.

Of the new infections, 2,010 (51 percent) were classified as neuroinvasive disease - meaning they may cause meningitis or encephalitis - and 1,959 (49 percent) were classified as non-neuroinvasive disease, sometimes referred to as "West Nile fever."

About 80 percent of people infected with the virus won't show any symptoms, but 20 percent may develop a fever, headache, body ache, vomiting, swollen lymph glands or a skin rash, known as non-neuroinvasive West Nile.

But about one in 150 however will develop severe neuroinvasive illness, with high fever, neck stiffness, convulsions, vision loss, paralysis, coma and other neurological effects that may be permanent - or even death. People over 50 and those with compromised immune systems are at the highest risk.

Preventing mosquito bites by reducing the amount of standing water present on property and by wearing an insect repellent with an EPA-registered active ingredient such as DEET are measures recommended by the CDC.

Almost 70 percent of the cases have been reported from eight states (Texas, California, Louisiana, Mississippi, South Dakota, Michigan, Oklahoma, and Illinois) and a third of all cases have been reported from Texas.

The CDC has more on West Nile virus.

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