Mosquito numbers stay same

Dry weather hasn't deterred pesky bugs

N.S. NOKKENTVED, THE OLYMPIAN

Originally published August 20, 2001

OLYMPIA -- A dry year has not affected the number of mosquitoes, but it has changed the species present in Western Washington.

The kind of mosquitoes that usually arrive here in mid-August have been here since May, said Tom Barton of the Cowlitz County Mosquito Control District.

But this year, because there was no flooding along the Columbia River, the area hasn't seen the kinds of mosquitoes associated with flooding, he said.

In some areas where local conditions have changed, the numbers and kinds of mosquitoes also have changed, Barton said. For example, mosquitoes that depend on cattails in Silver Lake disappeared when the lake was drained to repair the dam. With the lake level back up, so are the mosquitoes, he said.

But short rains followed by warm weather have allowed local mosquitoes to thrive, he said.

State health officials don't have numbers on mosquito populations, said Tom Gibbs, public health adviser with the Washington Department of Health. Mosquito control districts keep track of the pesky bugs. The districts were established to combat encephalitis carried by the common mosquito.

No encephalitis since 1980s

Most of the districts are in Eastern Washington. But a few districts were established in Western Washington, mostly in response to nuisance complaints, Gibbs said. Because of those mosquito control efforts, there hasn't been a case of mosquito-borne human-horse encephalitis in the state since the 1980s, he said.

Public health officials, however, have started to pay closer attention to mosquitoes again since the potentially deadly West Nile virus showed up in New York in 1999, he said.

Washington officials are working on response plans with the help of grants from the Atlanta-based Centers for Disease Control, Gibbs said. The virus is expected eventually to spread nationwide -- so far it has reached Ohio.

Efforts include monitoring dead birds and notification of veterinarians and doctors to look for symptoms of otherwise unexplained illness, Gibbs said. The virus is passed to humans and horses when they are bitten by mosquitoes that have fed on infected birds.

Through July, West Nile virus has been documented in Connecticut, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Florida, Georgia, Virginia, Ohio and the District of Columbia, according the CDC's Web site.

The virus can cause encephalitis, which can be fatal in severe cases.

In 1999, 62 cases of severe disease, including seven deaths, occurred in the New York area. In 2000, 21 cases were reported, including two deaths.

The fatality rate among severe encephalitis cases cause by West Nile virus is 3 percent to 15 percent and is highest among the elderly. Fewer that 1 percent of those infected with West Nile virus will develop severe illness.

People who survive may develop an immunity.

N.S. Nokkentved covers the outdoors for The Olympian. He can be reached at 360-754-5445.

The Olympian Copyright 2001

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