On the Trail of West Nile Virus

Experts can't predict where the mosquito-borne disease will surface this summer

TUESDAY, June 4, 2002 (HealthDayNews) -- When the West Nile virus first appeared in the United States in 1999, it was seen as an exotic, potentially deadly threat that created fear and confusion in the New York City area.

Since then, it has spread north to the Canadian border, west to Arkansas and Illinois and south to Florida. As of this year, the mosquito-borne virus has been identified in 27 states and the District of Columbia.

It's anybody's guess where it will show up this summer, experts say, so local health officials should plan for sooner rather than later.

There's been nothing like West Nile in the United States in about 300 years, when yellow fever was introduced into the Western Hemisphere during colonial times, says Durland Fish, an associate professor in the department of epidemiology and public health at Yale University's School of Medicine.

And while it doesn't pose a major risk to healthy individuals, people with weakened immune systems face such threats as encephalitis, even death.

"This has not happened in recent times, and so it's very difficult to predict what's going to happen. The virus has moved more rapidly than anyone really had anticipated," Fish says.

Scientists aren't able to forecast exactly where the virus will show up this summer, adds Chester Moore, supervisory research entomologist for the Centers for Disease Control and Prevention (CDC).

"There is no good way to even guess," Moore says.

For example, West Nile virus was expected to spread south from the New York City area in 2000. While it did move south to North Carolina, the main spread was north toward the Canadian border.

"In 2001, we expected that it would continue to spread, but it spread much faster than we had anticipated," Moore says. "So, I really don't think it's possible to guess what will happen this next summer."

Both Moore and Fish agree that West Nile virus is in the United States to stay, and it will eventually spread across the entire country.

"I think it's a major public health threat," says Dr. Richard Levinson, associate executive director of the American Public Health Association.

However, he adds, it isn't exactly the plague.

"It's not going to sweep the nation in an epidemic involving thousands or millions of people, but it will keep cropping up from time to time," Levinson says.

Romania and Israel, for example, have had outbreaks of West Nile virus involving several hundred people.

The virus was first identified in Uganda in 1937. Today, it's commonly found in Africa, West Asia and the Middle East.

It travels primarily between mosquitoes and birds. But infected female mosquitoes can transmit the virus to humans, horses and other animals when they take a blood meal.

Moore says there are 26 species of American mosquitoes identified as carriers of West Nile virus, but only about six are considered major transmitters of the virus.

In 1999, there were 62 confirmed human cases of West Nile virus, resulting in seven deaths. In 2000, there were 21 human cases leading to two deaths, and in 2001 there were 48 cases that resulted in five deaths, according to the CDC.

People who are healthy needn't panic if they become infected, since the symptoms are usually mild and include fever, headaches, body aches, skin rashes, and swollen lymph glands, says the National Institute of Allergy and Infectious Diseases.

Only those with weakened immune systems, such as people with cancer or AIDS, face greater dangers, one of which can be encephalitis, an inflammation of the brain.

If West Nile virus appears in your area, you need to protect yourself and your family against mosquitoes. The mosquito species that carry the virus are dawn and dusk feeders, so avoid going outside at those times, Levinson suggests.

Wear protective clothing and use insect repellent. And get rid of any standing water from your property to eliminate mosquito breeding sites.

"That's the major thing that an individual can do to protect themselves -- just keep away from mosquitoes," Levinson says.

"For the average person, they should find out from the local health officials, if they can, just what level of virus activity occurs in their specific area," Fish says.

He notes the majority of states affected by West Nile virus have surveillance programs that monitor bird and mosquito populations.

"There's certainly no cause for panic or anything. The chances of getting a serious infection, from what we know at this point in time, is fairly low," Fish says.

In March, U.S. government scientists announced they've developed a vaccine that protects mice from West Nile virus. They hope to begin human trials late this year.

However, Levinson has doubts about a vaccine. He's not convinced it would be cost-effective because the number of cases and locations of West Nile virus will vary year to year.

"So, any program of massively immunizing the population against (the virus) would be very wasteful. If you give (the vaccine) to 300 million people, and a 100 people get (the virus) every two years, it's really quite wasteful," Levinson says.

Even giving the vaccine to people in an area where West Nile virus has been detected wouldn't be efficient, he says.

What to Do: For more information about West Nile virus, go to the Centers for Disease Control and Prevention, or the National Institute of Allergy and Infectious Diseases.

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