As if you need another reason to loath the mosquito, this year a deadly outbreak of the west nile virus infected people in nearly every state in this country. A virus spread by the blood-sucking pest.... See More
As if you need another reason to loath the mosquito, this year a deadly outbreak of the west nile virus infected people in nearly every state in this country. A virus spread by the blood-sucking pest. In dallas the infections so rapid the city declared a state of emergency. Dr. Richard besser brings us to the center of the outbreak. Reporter: Even this infectious disease expert can't explain what west nile virus is doing to the brain? When you came to the hospital how much do you remember? Zero. Reporter: As he walks these halls, he had few answers for the west nile patients still fighting. I'm well known for being a straight talker. I don't know if I'll make it. You can see the white spot Reporter: This is a brain destroyed by west nile. Changes that go along with brain damage. Reporter: Even the doctor can't explain the white areas, all he knows is the body count is rising. Go, dad. Reporter: This is joe. Days later he thought he had the flu. Then it hit. Now he needs help getting in and out of bed. . My biggest thing it's between the fever. I get fever and chills really bad. All your joints hurt. You see somebody like that who can't even touch his nose with his finger. That's pretty scary. Reporter: West nile first arrived from africa more than a decade ago. Now birds and mosquitos have spread it across the entire country. No vaccine and no secure. The epicenter of the outbreak now is here in north texas. Reporter: If there's any hope of stopping it. It's here. Ft. Collins,colorado, the cdc's disease bourne laboratory. We're primarily interested in female mosquito, they feed on the blood. You see there's a white band? These are bad girls. Reporter: We're trying to find out what pesticides kill mosquitos. How long will it take to kill these? About 15 minutes. Reporter: We see how pest sized are fine-tuned down to specific neighborhoods. In the same city they may need different pestes. They are well adraapted to survival. Keep your eye on the bottle. Five minutes later they're on the bottom. Reporter: It works in the lab -- you had 5,000 trapped -- in one evening, yeah. Reporter: That's before they spread. If the formula works -- a few little bugs but nothing that looks like a mosquito. Reporter: This is not without controversy. Especially in dallas where spraying lead to complaints. The amount of pesticide is less than an ounce percent acre. It's minuscule. We've found no respiratory illness. Reporter: It's a fight that's personal for lyle petersen. What's the story on this? No repel lent makes virus guru -- I went out and both my friend and I got west nile virus. A healthy, middle-aged guy gets an illness? Yeah, I'm a long distance runner. I run marathons, I could barely walk up the steps. Reporter: Back in dallas joey has been in bed for five days. Are you ready to stand up? He's been in the vulnerable state. It's really hard. Reporter: The nights are the worst. It's 12:30. He seems to be resting a little more. He still has a headache. Good morning, good morning, everyth everybody. The next morning joey is stronger. Not quite ready for the trampoline but he's ready to go home. We're going home. Reporter: But for some of the other patients the road back will be much longer. We're unable to explain why some get better and others do not. Reporter: Only 1 in 150 get this sick but this year it's 1600 people. What's the chance we could knock out west nile from the u.S. There's a 0% chance we can knock out west nile. It's here to stay. In the early fall and late summer they're at risk. Reporter: I'm dr. Richard from ft. Collins colorado.
This transcript has been automatically generated and may not be 100% accurate.