June 16, 2005

Taking a Bite Out of Disease-Bearing Mosquitoes

Tulane researcher seeks to build a better bug trap

For almost an hour at a time, twice a day, two days a week in the deep heat of a Louisiana summer, Dawn Wesson stands in an urban backyard like a human scarecrow, arms spread wide, trying to attract mosquitoes.

She wears no repellant, but she does wear full protective gear, including a lightweight coverall with head net and gloves. The two species of mosquitoes that can transmit yellow fever and dengue fever will be attracted to her odor and try to land.

The last case of locally transmitted yellow fever in New Orleans occurred 100 years ago this week, but the mosquitoes have remained. In many other parts of the world, however, they still do transmit the potentially fatal disease.

Which is why Wesson, who holds a doctorate in medical entomology and is an associate professor of tropical medicine at the Tulane School of Public Health and Tropical Medicine, has volunteered to be a "human landing collection." This is the gold standard for the collection of mosquitoes that like to feed on humans or other large mammals, even now in the 21st century.

Wesson has about 30 seconds between the time a mosquito lands, and when it starts to feed, to catch it. The idea, she explained, is to ambush the insect from up above or behind using a simple suction hose. Wesson positions the hose then sucks with her mouth. There's a screen halfway up the tube so no insects end up in her mouth or nose.

"It's a bit of a game," Wesson said. "You don't catch them all, that's for sure."

The ones that do get caught end up in colonies in Wesson's lab. The purpose: to help Wesson develop a "mosquito motel," where bugs can check in but can't check out.

If the idea is successful, Wesson hopes the traps will be distributed to areas of the world where yellow and dengue fever are still rife. But they could also be used in areas where mosquitoes -- such as those that carry West Nile virus -- are less dangerous but still worrisome, places like Atlanta or Houston or New Orleans.

The goal is to attract and kill enough mosquitoes in a given area so they won't be able to transmit disease.

Like her collection methods, Wesson's prototype trap looks like it will be surprisingly low-tech.

The "motel" consists of a black plastic cup that appears as if it were borrowed from a fraternity beer party, only this one says, "Do Not Disturb. Mosquito Collection in Progress."

Approximately 50 such cups can be found in secluded, shady sites around New Orleans, mostly people's backyards. Inside are seed germination papers where the female mosquitoes lay their eggs. Researchers collect the paper once a week so the larva don't hatch in the field.

The mosquito motel will eventually contain a compound to attract females as they look for a place to lay their eggs (female mosquitoes are more problematic than males because they suck blood -- and transmit disease -- while males only feed on sugar).

The final trap is likely to be red or black (mosquitoes like dark colors, something to remember next time you're dressing for the outdoors) and will have compounds both to attract the insects and to kill them.

As Wesson pursues her research, blood is a key weapon against the pesky bugs. Once a month, a student drives 45 minutes to a slaughterhouse and buys cow blood for $10 a gallon. Once a week, the mosquitoes feed on this blood, heated to human temperatures. "They have water, sugar and the occasional blood meal and they're pretty happy in there," Wesson said.

But it's a short, happy life as Wesson and her fellow researchers study the mosquitoes' breeding and behavior patterns, with the ultimate aim of finding ways to attract and kill the bugs, thereby controlling the diseases they can spread.

In the meantime, Wesson is focusing some of her attention back home. She recently received a grant from the U.S. Centers for Disease Control and Prevention to track West Nile virus and pregnancy. In 2003, there were more than 70 documented cases of pregnant women contracting West Nile. Some of these women had babies with birth defects or who died, but so far there is no concrete evidence that West Nile infection was the culprit, she said.

This year's West Nile cycle is likely to hit the West Coast hardest, Wesson said, although Louisiana has already had positive mosquito pools as well as birds that have tested positive for the disease.

More information

Tulane School of Public Health and Tropical Medicine

For more on West Nile Virus, visit the U.S. Centers for Disease Control and Prevention (www.cdc.gov ).