Arizona hardest hit by West Nile
By Meriah Doty
CNN
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| | WEST NILE'S REACH | The West Nile Virus, first identified in 1937 in the West Nile region of Uganda, spread to the United States five years ago.
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(CNN) -- The pace of this year's epidemic of West Nile virus infection in humans appears to be outstripping last year's, with Arizona home to the largest number of cases, according to recent federal figures.
So far this season, 265 cases of the disease have been identified in 18 states, up from the same time last year, the Centers for Disease Control and Prevention in Atlanta, Georgia, reports.
As of Tuesday, Arizona has reported 161 cases, almost half of the total of human cases in the United States this year and more than 10 times the number it reported last year.
"We're really in the eye of the storm," said Michael Murphy, communications director for the Arizona Department of Health Services.
Many experts had predicted earlier this year that California would be the epidemic's hotspot. State officials there have reported 42 human cases to the CDC so far this year, a jump from a total of three last season. They've also attributed the state's first death to West Nile.
But Murphy said California will have to wait probably at least until next year to hold the dubious distinction of most West Nile cases, given Arizona's numbers.
"A lot of people think this is a dry desert state," said Murphy. But Arizona has many unnatural sources of water like pools that aren't well maintained, irrigation, golf courses -- places where mosquitoes can breed, he said.
Dr. Robert Tesh, a professor at the Center for Tropical Diseases at the University of Texas Medical Branch, is one of those experts who sees California as a potential area for a large outbreak.
"If you look at the pattern of the virus ... each year it seems to move West," he explained, also noting that California contains a big population of the type of mosquito most responsible for transmission of West Nile in humans and birds.
Last year, Colorado reported the highest number of West Nile cases and deaths, followed by Nebraska, South Dakota and Texas.
Murphy's fear is the number of human cases in Arizona will explode during monsoon season. "We could have numbers like Colorado did last year -- as many as 3,000 [cases of human infection]."
Last year, federal figures show 9,862 cases of human infection, 264 of them fatal. The case count typically ramps up the last part of the summer.
At least six people have died from West Nile this year, according to the CDC. Two died in Arizona; the others in California, Texas, Ohio, and Iowa.
This year, 49 percent of U.S. cases reported in humans have been the disease's more severe forms -- West Nile meningitis or West Nile encephalitis, which causes swelling of the brain.
The less severe West Nile fever has occurred in 31 percent of U.S. cases; the remaining cases did not provide that information to the CDC.
West Nile virus is primarily transmitted by the bite of an infected mosquito. Most people who become infected have mild or no symptoms. According to the Food and Drug Administration, an estimated one in 150 people infected develop the more severe form of the disease.
A vaccine is several years away from hitting the market, but even a government-approved vaccine should only be used on select groups of people, according to Tesh.
"You probably don't want to vaccinate the whole population," he said, because of the small risk of actually contracting severe forms of West Nile.
Those who would benefit from a vaccine, Tesh said, are those who are more likely to get a severe form of West Nile, such as the elderly or people with weakened immune systems -- cancer or transplant patients, for example.
"We know that elderly people are at higher risk," he said. Lab workers who are in frequent presence of the virus also would be good candidates to get vaccinated.
