Bzzt. Beware of mosquitoes: This is the worst year on record for West Nile virus. As of Wednesday, health officials have reported more than 2,600 cases, with the death toll hovering around 120 nationwide. That's the highest year-to-date total since the mosquito-borne disease was first detected in the United States in 1999.
"This is a wake-up call for public health," says Paul Biedrzycki, director of disease control and environmental health for the City of Milwaukee Health Department. "It's an emerging disease that we don't know a lot about, and it caught many officials off-guard. It was pretty quiet for a few years, and we became a little complacent—but now we're seeing an explosion in cases."
Texas has been hardest hit, accounting for about 45 percent of reported cases. Oklahoma, Louisiana, Michigan, South Dakota, and Mississippi are also experiencing particularly bad outbreaks. Last month, health officials in some parts of Texas turned to aerial insecticide spraying to reduce the mosquito population. Still, the number of reported cases is expected to climb through October.
West Nile spreads when mosquitoes feed on infected birds, and then bite humans and horses. It can also be transmitted through breast-feeding, blood transfusions, and organ transplants, says Gregory Poland, director of the Mayo Vaccine Research Group at the Mayo Clinic in Rochester, Minn.
Experts aren't exactly sure what's behind this year's outbreak, but they speculate that a mild winter, early spring, and especially hot summer contributed. These are ideal breeding conditions for the Culex mosquito, which carries the virus. "There may also be increased recognition of what's going on," Poland says. "We think about it more often and are more likely to detect it. I'm convinced that a handful of years ago, I was seeing patients who had mild symptoms, but it wasn't clear that West Nile was what was really going on."
Most people infected with West Nile have no symptoms. About 20 percent develop mild symptoms, like a fever, headache, muscle pains, a skin rash, and swollen lymph nodes. Fewer than 1 percent, or one out of every 150 people infected, become seriously ill with symptoms ranging from a high fever, neck stiffness, extreme muscle weakness, tremors, convulsions, and disorientation. If you have a fever over 100 degrees for more than two or three days, or neck stiffness not caused by physical exertion, see a doctor. Young children, adults over age 50, and those with compromised immune systems are most at risk of developing severe symptoms.
There's no treatment for West Nile itself, and as of right now, no vaccine—though both Biedrzycki and Poland expect one to be developed in the near future. Milder symptoms typically improve on their own. But severe symptoms warrant professional help. "We can treat symptoms," Poland says. "If you develop swelling in your brain, there are ways we can reduce that swelling."
Once someone is infected with West Nile, symptoms take between two days and two weeks to appear. Right now, we are at peak activity. "The end point will be the first frost, when mosquitoes are generally killed off," Biedrzycki says. "That takes us into October—and then a little beyond to account for the incubation period."
Until then, here's what you can do to protect yourself:
• Watch what you touch. "You don't want to handle dead birds," Poland says. In the United States, crows, robins, and members of the thrush family are most commonly infected with West Nile.
• When you're outside, use insect repellent that contains a U.S. Environmental Protection Agency-registered active ingredient, such as DEET and Picaridin.
• Mosquitoes are most active at dusk and dawn. Stay inside at those times—or wear long sleeves, long pants, socks, and shoes to protect against bites. Since the bugs can bite through thin clothing, spray it with repellent ahead of time.