Protecting Against West Nile Virus

For Immediate Release: Thursday, June 11, 2009

It's time to send out the West Nile Virus alerts for mosquito season, but Kenny Carver already started his annual campaign against the insects in Washington County. Carver, a 2004 graduate of Eastern Oregon University, hadn't planned to become an expert in mosquito abatement, but his work in Union and Multnomah counties prepared him for his current assignment: to protect the people in Washington County from the West Nile Virus carried by mosquitoes. He now works for Washington County as the Mosquito Control Coordinator.

His adversary is formidable. "There are mosquitoes that thrive in the cold waters of Alaska and other species that inhabit hot springs," Carver reports. Almost anywhere that water sits in ponds, backwaters, bird baths, and the drains in parking lots (called catch basins) and along gutters will harbor mosquito larvae.

Carver's main job is "surveillance," looking for spots that mosquitoes have started to breed. He uses a dipper in ponds and catch basins to catch larvae. He collects recently dead birds and tests them for West Nile Virus. And he has traps that use dry ice (mosquitoes are attracted to carbon dioxide), little fans and netting to capture adult mosquitoes so he can test them for the virus.

The first approach that Carver uses to control mosquitoes is to eliminate their "viable habitat:" buckets, old tires, and planters that collect water are easy targets and easy to deal with, just empty them out. "Homeowners can be really helpful by being sure that places with standing water on their property where mosquitoes breed are drained," according to Carver. "Birdbaths are fine as long as the water is changed at least once a week. Swimming pools that are properly chlorinated won't support mosquito larvae, either." 

Sometimes water gathers when there is a drainage problem. Carver works with the property owners to stop the source of the water, or move it away from where water can gather into pools. 

"When it comes to treatment of self-contained water bodies, our first line of defense is mosquito-eating fish, called Gambusia," says Carver. From his office, he gives away hundreds of the almost translucent two-inch long fish for free to homeowners, farmers, timber mills, and businesses. Mosquito fish are non-native to Oregon and therefore state law restricts their use to self-contained water bodies which are not fed or drained by natural waterways.

If Gambusia aren't enough, Carver and his team plant a "larvicide" in mosquito breeding habitat throughout the county. The larvicide is actually a naturally occurring bacterium found in soil, BTI, for bacillus thuringiensis israelensis, contained in small pellets.

Carver also works with other government agencies, schools, shopping centers, and other businesses, apartment buildings and anywhere people gather to provide education and services. "We'll help the owners understand what they can do to eliminate mosquitoes."

In Washington County, Carver has found West Nile Virus in birds but not yet in mosquitoes, horses or people.  About 80 % of the people who get it have no symptoms and usually don't even know that they had it. 

But approximately 20% of people who get West Nile virus will experience mild, flu-like symptoms. Less than 1% will develop severe illness – usually people older than 50 years, or with hypertension, diabetes or who consume high levels of alcohol.

"We don't want to create fear," says Carver, "but we want to encourage people to take practical protective measures." 

He suggests:

• Eliminate breeding spots around your home: empty buckets, drain old tires, clean out rain gutters, change water in bird baths and similar fixtures at least weekly.
• Wear protective clothing when you're out in the mornings and evenings, when mosquitoes are most active.
• Check to be sure screens in your home are secure.
• Use a mosquito repellant with DEET in it, or natural repellents like picaridin or oil of lemon eucalyptus.

To contact Kenny Carver for information or to obtain free Gambusia fish, call 503-846-2904.

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