No one's sure if the West Nile virus will come to Alaska, but experts at the Centers for Disease Control said they think there's a limited possibility, according to Louisa Castrodale, epidemiologist for the Alaska Department of Health and Social Services.
The virus, which has made its way across the eastern half of the United States this year with 113 human cases reported as of Thursday, has caused five deaths -- all in Louisiana.
One case reported in Washington state actually involves a Washing-ton resident who had spent time traveling in Louisiana at the time of infection, Castrodale said.
The virus also has spread across eastern Canada, to as far west as Manitoba, above Minnesota.
"We don't have West Nile in Alaska at this point," Castrodale said. "We might not have the right kinds of mosquitoes for it to spread here."
West Nile is spread by the mosquito species "culex."
The virus, as described on the Centers for Disease Control and Prevention Web site, is spread by the bite of an infected mosquito and can infect people, horses and many types of birds.
"Most people who become infected with West Nile virus will have either no symptoms or only mild ones. On rare occasions, West Nile virus infection can result in a severe and sometimes fatal illness known as West Nile encephalitis (an inflammation of the brain)," according to the Web site.
The virus is transmitted continuously by mosquitoes blood feeding on birds. Infectious mosquitoes then bite humans, horses or other mammals.
Castrodale said the spread of the virus is tracked by watching for dying birds and by setting out mosquito traps in areas where cases have been reported.
She said the Alaska health department "has been talking about getting together with the Centers for Disease Control and the University of Alaska at Fairbanks to do active surveillance before we see any cases here."
The CDC Web site states human illness from the virus is rare, even in areas where the virus has been reported.
"The chance that any one person is going to become ill from a mosquito bite is low," it states.
To reduce chances of becoming ill, CDC advises use of insect repellent when outdoors, wearing long-sleeved shirts and long pants, staying indoors especially during peak mosquito feeding hours -- dusk until dawn -- and limiting the number of places where mosquitoes lay their eggs by eliminating standing water sources around homes.
The number of West Nile virus cases reported in humans in the United States this year are one in Alabama, one in Illinois, 71 in Louisiana, 28 in Mississippi and 12 in Texas.
"There's a vaccine for horses, not for people," Castrodale said.
The CDC reports that a virus vaccine for horses recently was licensed, but its effectiveness is unknown. In locations where the virus is circulating, horse owners are instructed to protect horses from mosquito bites as much as possible.
The virus was first isolated in the West Nile district of Uganda in 1937. It has since been found in Africa, Europe, the Middle East, Asia and, most recently, North America. It first appeared in North America in 1999.
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