This year's outbreak of West Nile virus is on track to be the deadliest on record, according to the Centers for Disease Control and Prevention. The human toll from the mosquito-borne disease rose by about 35 percent, overall, since Sept. 6, to 2,636 cases, including 118 deaths.
"We still believe that this year's outbreak is the largest to date and certainly the most serious," said Lyle R. Petersen, M.D., director of the CDC's Division of Vector-Borne Infectious Diseases, at a press conference.
As of this week, 1,405 (53 percent) of the West Nile virus cases have been classified as severe enough to affect the nervous system, in some cases causing encephalitis (inflammation of the brain) or meningitis (inflammation of the membrane around the brain and the spinal cord).
"We're not out of the woods yet, by any stretch of the imagination," Petersen said. He expects large numbers of cases to be reported for the next several weeks. Moreover, between 8 and 10 percent of the people who develop neuroinvasive disease will eventually die because of the infection, he said.
The largest human toll from West Nile virus in the U.S. was in 2002, when 2,946 people fell ill with neuroinvasive disease and 284 died.
"Based on historical data, we should either catch up or surpass the previous numbers as cases continue to roll in," Petersen said.
Forty-five states and the District of Columbia have reported at least one human case of West Nile virus, so far this year. Two-thirds of the cases have been in six states (Louisiana, Michigan, Mississippi, Oklahoma, South Dakota, and Texas) and 40 percent of all cases have been in Texas.
There is no specific treatment for West Nile virus infection. But people with symptoms should see a doctor because some medical interventions might be needed to support the body's functions until the infection clears.
Bottom Line: It's important that people continue to take steps to avoid mosquito bites. That includes using an insect repellent when going outdoors, wearing long-sleeves and pants during dawn and dusk, installing or repairing screens on windows and doors, using air-conditioning if you have it, and emptying standing water from items outside your home such as gutters, flower pots and buckets. Check our insect repellent Ratings and read our report on how to deal with Mother Nature's rashes and bites.
2012 West Nile virus update [CDC]