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November 10, 2008
Bug hunters net clues to West Nile virus

By CAROL Clark

If you’ve walked along Peavine Creek near campus this fall, you may have noticed a group of students stalking mosquitoes. For months, they have dipped up eggs and larvae from stagnant pools. They’ve also set traps in trees and vacuumed the air to snag flying adults, using a backpack aspirator that looks like the nuclear accelerator from “Ghostbusters.”

“It’s a bit of an adventure,” says Gonzalo Vazquez Prokopec, a postdoctoral research associate, stepping from stone to stone in the creek.

“No mosquitoes,” he reports, as he checks a trap baited with a chemical that mimics the scent of human sweat. “This site is pretty pristine. When we go to our other research sites, along Tanyard Creek, we can easily find 500 females in one of our traps. Here, we get only 150 of them, max.”

Prokopec is a leader of the Emory team that is collaborating with the CDC, the University of Georgia, and health officials from the state and Fulton County to solve a mystery surrounding West Nile virus: Why have clusters of human cases in Atlanta occurred near streams that occasionally get raw sewage runoff, known as combined sewer overflows?

Luis Chaves, another postdoctoral researcher, and Uriel Kitron, chair of environmental studies, are also leading the project. Seven students, and two research assistants, are doing fieldwork and getting hands-on experience.

“It’s amazing how much you can learn when you work on a project like this,” says Alexandra Van Nostrand, a senior majoring in environmental studies.

West Nile virus is a mosquito-born virus that was first detected in the United States in 1999 during an outbreak in New York. The virus gradually spread to other states, carried by infected birds. Georgia reported its first human case in 2001.

The Tiger mosquito is the common backyard pest in Georgia that attacks any bare patch of skin. But it’s a different type of mosquito, Culex quinqufasciatus, that is the main vector here for West Nile virus.

“The Culex mosquito bites birds that are infected with West Nile Virus, and it also bites humans,” Prokopec explains. “That creates the bridge, that carries the virus to people.”

The researchers are doing a comparative analysis of mosquitoes and water samples from sites along Peavine Creek, which does not get combined sewer overflows, and Tanyard Creek in Buckhead, which does. Their preliminary results have confirmed that the Culex mosquitoes are much more prevalent in the sites with sewage runoff. They are now trying to zero in on the reasons why.

“The fieldwork can get grimy, but it’s also fun,” says An Nguyen, a sophomore majoring in environmental studies. “We are analyzing what’s in the polluted water, to see if something is making it tasty to the mosquitoes. It makes me feel good to help fight a serious disease.”

As the cooler weather keeps the mosquitoes dormant, the researchers will focus their work in the lab, where they have meticulously counted, weighed and frozen hundreds of the bugs. The mosquitoes will be analyzed to determine if they carry the DNA of West Nile virus, and to learn whether their final blood meal came from a human or an animal.

Van Nostrand is taking a class in geographic information systems, and will be generating maps for spatial analyses of how vegetation and socio-economic factors could protect against the disease. “We know there are Culex mosquitoes in Fulton County,” she says. “What we don’t know is why the rate of human cases of West Nile virus is so low.”

The researchers hope to get funding to keep the project going long-term. Studying urban mosquito ecology can provide baseline data that could later prove useful for many emerging diseases. For instance, the pervasive Tiger mosquito is a potential vector for pathogens such as the deadly Chikungunya virus, which is native to Africa and Asia but recently caused an outbreak in Italy.

“Mosquitoes are a big concern of most health departments, but they don’t usually have the funding or personnel to do rigorous, standardized studies of them,” Prokopec says.

To learn more about the project, visit: http://www.envs.emory.edu/research/WNV/index.htm.