West Nile Virus Victims Younger This Year, U.S. Says

For reasons that health officials cannot explain, this year’s victims of the mosquito-borne West Nile virus are younger than usual.

The median age for this year’s infections is 55, the federal Centers for Disease Control and Prevention here said in a report Thursday. In previous years, the median was in the mid-60s.

“The reason patients seem to be younger this year is unknown and certainly something we’re looking into,” the CDC’s Dr. Lyle Petersen said.

However, CDC officials said the declining median age is not a cause for immediate concern.

The CDC has reported 112 human cases this year, more than half in the last week.

Most of those cases were in Louisiana, which has reported 71 infections and five deaths in the nation’s biggest outbreak since the disease was first detected in New York in 1999.

A central Mississippi man who died Thursday likely was killed by the West Nile virus, state health officer Ed Thompson said. He said more testing was needed to confirm preliminary results. The death would be the first outside of Louisiana in this outbreak.

Mississippi has reported more than 30 human cases of the disease. The CDC also reported human infections in Texas and Illinois. Cases also were announced this week in Alabama and Washington, D.C., but came too late to be included in the CDC report.

In addition, Illinois reported its second human case Thursday, a 57-year-old man who became critically ill with encephalitis.

Kansas officials said Thursday that the virus has spread to their state, where it was found in a dead horse. In Missouri, 13 horses that died from encephalitis--a swelling of the brain--also have tested positive for West Nile at the University of Missouri’s Veterinary Medical Diagnostic Laboratory in Columbia.

On Thursday, the CDC announced that an additional $10 million will be sent to states to fight infected mosquitoes. The agency already handed out $17 million a year, but as more states requested help, the fund didn’t cover requests. About $3.7 million will be earmarked for Louisiana and Mississippi, the hardest hit states.

Most people bitten by infected mosquitoes will suffer no more than flu-like symptoms, but the weak and the elderly can get encephalitis, a potentially fatal brain inflammation.

Petersen said advanced age remains the biggest risk factor for getting sick from the bite of an infected mosquito. Health officials do not compile statistics on any health problems the younger West Nile victims had, but suspect that many had conditions that weakened their immune systems.

Men made up 60% of this year’s West Nile cases, consistent with years past. Petersen said that is probably because men spend more time outdoors.

Gary Simon, an infectious-disease expert from George Washington University in Washington, said doctors may be more aware of the disease and likely to look for it in patients with less serious symptoms, explaining the lower median age.

“It may be because we’re testing people more,” he said. “It’s the only possible explanation from the information I’ve seen so far.”

Since its first appearance in the United States, the virus has been detected in 35 states and the District of Columbia.

State and local officials have boosted mosquito-spraying efforts and urged people to protect themselves by using insect repellent and wearing long sleeves.