AUDIE CORNISH, HOST:
West Nile Virus is back and the mosquito-borne infection is looking pretty nasty this year. As NPR's Rob Stein reports, federal health officials are trying to get out the message: protect yourself.
ROB STEIN, BYLINE: The West Nile Virus first appeared in the United States in 1999 and quickly spread from coast to coast, raising widespread alarm. As it turns out, most people who get infected never know it or recover after just a bad fever, nasty headache and other symptoms. But about one percent of who get the virus develop serious complications, such as encephalitis or meningitis.
Roger Nasci is with the Centers for Disease Control and Prevention.
ROGER NASCI: About 10 percent of those people die and then a substantial portion of them, 50 percent or greater, have serious after-effects with paralysis, headaches, severe neurological damage as a result of what the virus does to the nervous tissue.
STEIN: There's already been at least 241 cases of West Nile disease reported in 42 states this summer. Of those, 144 have been these serious infections. At least four people have died. There haven't been this many cases this early in the season since 2004.
NASCI: The bulk of the West Nile cases in the U.S. generally occur in August and September and we're just entering August and we've already seen this uptick compared to previous years.
STEIN: Most of the cases have occurred in just three states: Texas, Mississippi and Oklahoma. But cases are popping up all around the country. Nasci says the reason for the increase is complicated, but the unusually warm winter, early spring and hot summer is playing a role.
NASCI: The conditions were just right to really kick up the number of infected mosquitoes and that translates into the greater likelihood that infected mosquitoes are going to bit people and then they get infected and a proportion of them show these symptoms.
STEIN: So health officials are encouraging people to protect themselves. Do things like fix your torn window screens, use insect repellents, wear long sleeves and pants and try to stay inside at dawn and dusk.
NASCI: It's not a run-for-the-hills-panic type of thing, but awareness and some personal protection certainly can go a long way to reducing your likelihood of getting infected.
STEIN: Rob Stein, NPR News.