So in places like Fairfax County, Va., they keep a close eye on mosquito traps.
"I have a lot more respect for West Nile virus today than I ever had before," said Jorge Arias, who heads the program. He said he would've shown us the traps personally but it's hard for him to walk; he was infected with West Nile himself two years ago, and is still partially paralyzed as a result.
But he'd be the first to tell you that there are worse things than West Nile out there.
Kimberly King never gave mosquitoes a second thought until her five-year-old daughter Adreana was bitten by a mosquito carrying the rare Eastern Equine Encephalitis, or EEE, somewhere near their home south of Boston.
"We could have been swimming, we could have been hiking in the woods, we could have been fishing," said King. "We could have been sitting on the back porch. We could have been driving in the car."
The girl went to her mother saying she didn't feel well: "She seemed to have flu-like symptoms," said King. "And then within 24 hours of her first symptom, she was seizing."
After a week in intensive care it was clear that the little girl would not recover.
"We had to make the decision to take her off the life support," said King. "And we took her off the life support, she was in my arms. I was holding her as she died.
"They took her off all of her machines and her hoses in my arms, and they allowed me to help wash her up before they sent her down to the morgue."
Kimberly King buried her daughter on the day she would've started kindergarten. She's become a full-time advocate for mosquito repellant and control, as a commissioner at the Plymouth County Mosquito Control Project.
But she says she doesn't feel like the unlucky one in a million: "There were others before me, and unfortunately, there'll be others after me," she told Smith.
Still, death by mosquito is extremely rare in the U.S. In 2010 just over 100 people here died of mosquito-borne diseases. Those numbers would be higher, experts say, if not for aggressive mosquito control.
Shelley Redovan, executive director of Lee County Mosquito Control District, said her arsenal includes around a dozen aircraft that cover the 1,200-square-mile county, spraying for mosquito larvae that breed wherever there's standing water - which, down here, can be pretty much anywhere.
And in Florida, where the bugs naturally thrive, it's about more than public health.
"It used to be that tourists would come to Florida two months out of the year because that was the only time they didn't have that many mosquitoes," said Redovan. "But we have since been able to control them so we can have a tourist season 12 months out of the year."