May 28, 2004

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COLLEGE STATION - A graduate student's class project is helping cities in Brazos County target hot spots for the West Nile virus and the mosquito that carries it.

Catherine Zindler, a research assistant and graduate student with the department of entomology at Texas A&M University, developed a map using geo-referenced and remote sensing data. The map will help Bryan and College Station concentrate control efforts for the Culex quinquefasciatus, or the southern house mosquito.

Zindler undertook the project in partial fulfillment for two classes with Dr. Sorin Popescu, assistant professor, and Dr. Raghavan Srinivasan, director of the Spatial Sciences Laboratory.

"We don't have a risk map for many areas, especially for the Bryan-College Station area," Zindler explained.

Dr. Jim Olson, Texas Agricultural Experiment Station entomologist, said, "The study gives a visual representation and spatial analysis of the highest risk areas for mosquitoes, birds and humans." This gives the cities of Bryan and College Station a better idea of where to survey and use control methods for the mosquitoes, he said.

Spatial sciences use a variety of mapping methods to give the location of features on the Earth's surface and enable people to see the interaction between them. "Without this, I wouldn't have been able to see the correlation between manhole covers, vegetation, flood plains and dead birds," Zindler said..

The southern house mosquito is the primary vector of the West Nile virus in southern and southeastern Texas, Olson said.

"It breeds in septic water, both above and below ground," he said. "It can't get too soupy for it ... the more waste in it the better."

For the computer-generated map, Zindler overlaid maps of flood plains, creeks and the location of manhole covers – an indication of sewer lines – with last summer's dead bird data provided by the Brazos County Health Department. Dead birds – especially cardinals and blue jays – are susceptible to and indicative of the virus' presence. She integrated remote sensing vegetative maps to indicate where birds are most likely to nest.

The result? The areas where the dead birds were found overlapped the areas with the manhole covers, she said.

The Harris County Mosquito Control District is trying to create a similar map, but the effort is slowed by the tremendous task of mapping all of the manhole covers in the area.

An animation of weekly dead bird locations allowed her to follow the progression of the virus last summer. It also followed the migration of birds from northern areas of Bryan to the southern areas of College Station. The map allowed Zindler and the county health department to pinpoint areas of high risk.

"If we don't have a risk map," Zindler said, "we have to wait until somebody becomes infected and sick—or we have a lot of dead birds—to know we should go in and test sites. People need to know if West Nile has been found in their community."

Brazos County reported five cases of West Nile virus in humans last summer. Each was found in a high-risk or very high-risk area on Zindler's map.

"If I'm living in a high-risk area, then I would want to take precautions. I would want to listen and do what I'm supposed to do: Wear my mosquito repellent and mow my yard in the hot part of the day so the mosquitoes won't bite me," she said.

The risk map also allows the county health department to plan its spraying program. Zindler said. "You don't want to spray areas with insecticides unless there's good reason to. We know this is where (the mosquitoes) rest, in sewers, but now we know that it's really actually important to spray the sewers."

The department of entomology will continue her project this summer by surveying those areas targeted as high risk. Mosquitoes will be collected from these areas at four locations once a week for eight weeks. Those will be sent to the Texas Department of Health for testing as to presence of West Nile.

And Zindler? She not only helped track West Nile virus in the county, but she got A's for the project and A's for the semester in both classes.