West Nile Virus Detected in 43 States

Texas declares state of emergency after victims die from mosquito bites.
3:00 | 08/15/12

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Transcript for West Nile Virus Detected in 43 States
new alarm from the cdc about an outbreak of the west nile virus. More widespread than they have ever seen before. The virus has now been detected in 43 states. It is carried by mosquitos. So, what is the first sign that you're in trouble? Here's abc's ryan owens from dallas, where they have declared a state of emergency tonight. It feels like somebody had lodged an axe in my brain. Reporter: If you think west nile virus only affects the elderly and unhealthy, meet kathryn DeVille. She's 42, mother of an 8-year-old, and in good health. At least she was until a mosquito bit her last month in her backyard outside dallas. Just about the time I think I'm out of the woods, something else comes along and we have to fight that, too. Reporter: You have felt mess rabl for more than two weeks. I have. Reporter: That one mosquito bite left her first with a fever of 104 and now with meningitis and encephalitis. Dallas is the epicenter of this epidemic. One quarter of the country's cases are in this wound county. Most people with the virus never know they have. Roughly 80% have no symptoms. 20% suffer from combination of high fever, headaches, joint pains, vomiting and diarrhea. Only about 1% develop the neuro invasive form of the disease that attacks the brain and spinal cord and can be fatal. We are starting to see younger patients get neuro invasive disease and that's unusual. Reporter: Communities across texas have been spraying pesticides every night. And by the end of the week some will start controversial aerial spraying. I don't want anyone to get this. So if that means they have to spray from the air fo it. Reporter: Doctors say kathryn will recover but she's already missed her daughter's first day of school, after a summer few here will forget. Ryan owens, abc news, dallas. I want to bring in abc's medical editor, dr. Richard besser, spent most of his career tracking diseases with the cdc. So, 400 people have already had the most severe consequences. What are we going to do about this? Reporter: It's very serious. And there is no treatment. So, the key here is rea all about prevention. And when you talk about prevention, the key is, fight the bite. If you don't get bit by a mosquito, you're not going to get this disease. The woman that we saw in this story, it doesn't always go away. 60% of people continue to have those neurological similarymptoms for five years. And where does it come from? Reporter: Well, mosquitos get it from birds. It is people who are over 50, healthy and active, they are outside, who are most likely to get the most severe kind of west nile virus. Very high fever and aches? Reporter: Aches -- it will seem like you have the flu. And if you've got the flu and it's in an area where there is west nile circulating, it could be this disease.

This transcript has been automatically generated and may not be 100% accurate.

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