A total of 1,590 cases of West Nile virus, including 66 deaths, were reported through late August this year in the United States, the highest human toll reported by that point in the calendar since the mosquito-borne disease was first detected in the country in 1999, health officials said on Wednesday.
The toll is increasing quickly and "we think the numbers will continue to rise," said Dr. Lyle Petersen, director of the U.S. Centers for Disease Control and Prevention's Division of Vector-Borne Infectious Diseases.
Through last week, 1,118 cases and 41 deaths had been reported. The updated figures represent a 40 percent increase in the number of cases and a 61 percent spike in the number of deaths, but are short of the all-time record for a full year: 9,862 cases and 264 deaths in 2003.
In hard-hit Texas, the number of confirmed cases soared to 733, up 197 from last week, said Dr. David Lakey, commissioner of the Texas Department of State Health Services. Deaths reached 31, up 10 from last week.
"It looks like it is going to be our worst year ever," said Lakey. "As I look at the data, I'm not convinced we have peaked."
All 48 contiguous states have reported cases of West Nile virus in birds, which act as hosts; in mosquitoes, which transmit it by biting birds and then mammals including humans; or in people. Only Alaska and Hawaii have been spared. And 43 states have at least one human case.
"The virus is endemic at this point throughout the United States," with the possible exception of high-altitude regions such as the Rocky Mountains, said the CDC's Petersen. "There is a risk almost everywhere."
So far, however, more than 70 percent of the human cases have been reported in just six states: Texas, South Dakota, Mississippi, Oklahoma, Louisiana, and Michigan.
Only 2 percent to 3 percent of cases of West Nile fever are reported to health officials, said Petersen, which suggests that the actual number of cases is 30 to 50 times higher than reported.
That is partly because an estimated 80 percent of infected people have no symptoms, said Dr. Robert Haley, of the University of Texas Southwestern Medical Center in Dallas, in an essay last week in the Journal of the American Medical Association.
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