Health & Science : Sunday, October 08, 2000

Imported virus expands range, types of victim

By Michael Ruane
The Washington Post

WASHINGTON - The disease has spread more than 300 miles since the initial
outbreak in New York. It has infected three times as many types of birds as
last year. And it now is being carried by eight kinds of mosquitoes.

West Nile virus, in evidence between the Washington, D.C., area and New
Hampshire, is thriving and expanding, experts said, and probably will spread
across the country within three years.

"Three years from now, I think it'll be over most all of the country," said
Ward Stone, New York state's veteran wildlife pathologist, who has watched
the virus since it first appeared in the United States last fall. "Three
years from now ... it will be a national problem."

The virus, first identified in Uganda in the 1930s, normally is not
dangerous to humans. But in children and senior citizens, it can cause
potentially fatal inflammation of the brain and its protective sac.

Transmitted by mosquitoes and transported mostly by birds bitten by the
insects, the illness first appeared in the United States last year. It
largely was confined to the New York City region, where it killed seven
people and made 62 seriously ill.

It survived the winter, and its spread continued this year.

Although anti-mosquito efforts this year have limited human fatalities to
one and serious cases to 17, the virus has alarmed scientists for other
reasons.

It has, for example, infected many more kinds of wildlife than it did last
year, from 20 to 60 types of birds and spreading out to mammals such as
chipmunks, raccoons and bats.

For unknown reasons, scientists say, it continues to particularly ravage
crows, producing a 100 percent fatality rate.

The virus has been found this year in eight types of mosquitoes - as opposed
to last year's lone culprit, the bird-loving Culex pipiens - and probably
will spread to more.

Most such viruses are borne by only a few kinds of mosquitoes, experts said.

In addition, several of the new mosquito types have a particular taste for
mammals and humans: Aedes vexans, for example.

"It's one of the most common mosquitoes in North America," said Maryland's
mosquito-control chief, Cyrus Lesser. "From the Arctic to Mexico, it's
basically everywhere." It aggressively bites birds, people and other
mammals, he said. "Whatever presents itself."

The added mosquito types are worrisome, Lesser said, because they may
increase the rate of transmission and involve mammals as well as birds. "It
opens a whole new world to the virus," he said.

The most striking change over last year, though, has been its geographic
expansion - hundreds of miles from the New York City region to almost all of
New England and the mid-Atlantic states this year.

Last year, the virus appeared in New York, Connecticut and New Jersey, said
Stone. This year, it also has cropped up in Rhode Island, Massachusetts, New
Hampshire, Pennsylvania, Maryland and Washington, D.C., and possibly Canada.

Robert McLean, director of the U.S. Geological Survey wildlife health
center, said the fear is that the virus is establishing itself in regions
north, west and south of its original area around New York. Next spring,
when birds migrate northward in their typical fan pattern, they could spread
the virus toward the Midwest.

Eventually, if birds carry it to the Gulf Coast, their migrations could
transport it up what is known as the Mississippi flyway and out to the rest
of the country, he said.

"I don't want to seem alarmist," McLean said. "But we are concerned."

Stone added: "Because we have a lot of species that have never experienced
this virus before, at least in the first few years, we can expect a very
heavy mortality rate in these birds.

"We can kind of think, although it's most likely to be on the eastern coast,
there's a good likelihood that it will spread to all parts of the country
where weather conditions and the right mosquitoes are there to maintain it.

"I'm pretty worried about what it's doing and what it's going to continue to
do to the wildlife of the country."

Stephen Guptill, a Virginia-base USGS physical scientist who has mapped the
virus over two years, said: "The thing we know for certain is that the virus
has established itself in North America. There was a chance that it could
have been a one-time event. It could have gone away.

"We know that's not the case," he said. "It's here, and it's here to stay."