The West Nile virus and Alaska

Posted: Sunday, January 19, 2003

At a quarter-inch to a half-inch long, and weighing about one-third of a milligram, one of the earth's tiniest animals poses a threat to some of the largest.

The mosquito ("little fly" in Spanish or Portuguese) can be any one of more than 2,500 species of fly found throughout the world. Roughly 200 species of the annoying, biting insects are found in the United States.

Mosquitoes will do more than spoil a hike; some varieties carry diseases that infect humans and other animals. According to the American Mosquito Control Association, the types of female mosquitoes that require a blood meal for their own egg production prefer horses, cattle, smaller mammals and birds over humans.

However, mosquitoes do bite people and some species spread "arthropod-borne viruses," or "ARBO viruses," when they sneak their bloody snacks. Yellow fever, dengue fever, St. Louis encephalitis and West Nile virus are all ARBO viruses, but it is West Nile virus, or "WNV" that has captured the attention of outdoor enthusiasts, public-health officials and the press over the past two years in America.

WNV is primarily a bird disease, and it has been detected in dead birds of at least 110 species in the United States. The virus also has affected humans, horses, bats, chipmunks, rabbits and squirrels.

In birds, WNV can cause depression, weight loss and elevated white cell count, progressing to tremors, mental dullness, blindness, clumsiness, weakness in the legs and eventually seizures.

Birds that do not become ill from the virus or recover develop a lifetime immunity. Some birds recover, but have lasting neurological disorders. Parrots, parakeets and other pet species may be less susceptible to the virus, but the evidence is not conclusive.

Birds of the corvid family - crows, ravens, jays and others - and some species of raptors are most susceptible to the virus.

The only regular transmission of WNV across species results from mosquito-bird interaction. A bird that has been infected by one - or likely several - mosquitoes, becomes a "reservoir" for the disease, like a bank from which other mosquitoes make withdrawals. Enough of the virus has to build up in the blood of an animal to be passed to others.

Only one percent of humans who are infected with the virus show symptoms. Symptoms in humans can include fever, a rash, swollen glands, muscle pain and weakness. Severe symptoms, such as encephalitis or meningitis, occur in fewer than one percent of all humans who develop symptoms, according to the Centers for Disease Control.

WNV, which originated in Africa, but has spread throughout Europe and the Middle East, was first diagnosed in birds, particularly crows, in New York City in 1999. Human cases began appearing shortly afterwards.

In 2001 WNV appeared in neighboring states, and by March 2002, had been documented throughout the eastern half of the country. Just five months later, WNV could be found in 44 states, excepting only Oregon, Utah, Nevada and Idaho, plus Alaska and Hawaii. It has appeared across southern Canada, with the exception of British Columbia.

Will WNV spread to Alaska? Researchers aren't sure.

"I wouldn't say it's an impossibility," says Dr. Emi Saito, West Nile Virus Coordinator for the U.S. Geological Survey. "Some speculate that it will be there by next season. We don't really understand the ecology of the virus and how it spreads."

Long suspected of being carried by migratory birds, Saito suggests they may not be the only factor in its spread. Experiments with small samples of birds in the lab have shown that birds fed with WNV-infected mice have contracted the disease, including crows and a great horned owl. But she cautions against reading too much into experiments with small samples, "This is preliminary evidence - is it really replicating what's going on out in nature?"

Some scientists are dubious that the virus could reach Alaska. Dr. Mark Schultz, an entomologist at the Forestry Sciences Laboratory in Juneau, is skeptical that a suitable reservoir for the virus will make its way to the state with the right timing to trigger the cycle of infection.

"You have to have a susceptible bird, and the bird has to make it here alive," he says. Then the mosquitoes have to feed from the bird and infect others - "the cycle has to repeat itself."

The best preventive measures against WNV are avoiding areas with high mosquito activity, wearing clothing that covers the skin and using bug dope that contains DEET. Eliminating standing water that attracts breeding mosquitoes also is advised, such as old buckets and tires, and other places where water can collect.

Dr. Jim Scott, a veterinarian and founder of Bird TLC in Anchorage, says "we need to avoid raising a panic about WNV, since no more than 2 percent of any species is affected by the virus." Some of the response to WNV illustrates this - in 2000, pesticides killed more birds in New York than WNV.

On Tuesday, Jan. 21, the Juneau Raptor Center will host a free public presentation on West Nile virus by Kimberlee Beckmen, wildlife veterinarian for the Alaska Department of Fish and Game in Fairbanks and a member of the state's West Nile Virus Working Group. The free program starts at 7 p.m. in the Dzantik'i Heeni Middle School library.

Southeast Wild is provided by the Juneau Audubon Society, which can be reached through its Web site at www.juneau-audubon-society.org.



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