West Nile cases nearing record

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Forty-one states and the District have reported 2,171 illnesses from West Nile virus so far this year, 74 of which have been fatal -- setting the stage for a likely increase in new cases compared with 2005, federal health officials say.

"There were 1,512 reported cases in 38 states -- including 41 deaths -- at that same point last year, and a total of 3,000 cases, including 119 deaths, by the close of 2005," said Dr. Lyle Petersen, director of the Centers for Disease Control and Prevention's Division of Vector-Borne Infectious Diseases.

"We predict we are going to exceed last year's [total case] figure by about 20 percent, which will make this the third-largest outbreak ever" in the United States, Dr. Peterson said, noting that the two worst years were 2002 and 2003.

West Nile arrived in this country in 1999 in New York. Through 2001, the CDC confirmed 149 cases in humans in the United States, including 18 deaths.

But the human caseload reached 4,156 in 2002, including 284 fatalities. In the 2003 outbreak, 9,862 cases and 264 deaths were reported by the CDC.

The national virus update for Sept. 19 is 437 cases, 18 deaths, and six states more than it was one week ago. The biggest virus problems have been reported by states in the West and along the swampy Gulf Coast.

Idaho leads the nation with 401 human cases, followed by Colorado with 199, California with 197 and Texas with 180. To date, Texas has experienced the largest number of deaths at 19, up from 13 last week. It is followed by Idaho, which has reported nine deaths, and Oklahoma, which has reported five.

Maryland and the District each had one confirmed human West Nile case, but neither reported a related death. Virginia has had two cases confirmed but no deaths.

Asked why the national total is expected to be high this year, Dr. Petersen said northern states west of the Mississippi were "abnormally hot, particularly in July." High temperatures allow mosquitoes to become infected faster.

Also, there were "elevated amounts of rain, and so a lot of mosquito breeding," he said.

Infected mosquitoes are the villains in human West Nile cases.

Birds are the main reservoir for West Nile virus. During the summer months, high levels of the virus are found in dead birds. Mosquitoes thriving in the same hot weather conditions contract the virus by feeding on infected birds. They transmit the virus when they bite humans.

West Nile can cause potentially lethal neurological diseases in people, such as West Nile encephalitis and West Nile meningitis. West Nile encephalitis is an inflammation of the brain, while West Nile meningitis inflames the membrane around the brain and the spinal cord. Among this year's cases, 829, or 38 percent, were reported as encephalitis or meningitis, the CDC reported.

A condition known as West Nile fever refers to less-severe cases that resemble influenza, which do not involve neuroinvasion. Fifty-eight percent of the 2006 cases, or 1,254, were mild. An additional 4 percent of total cases were clinically unspecified, according to CDC data.