AZ Partners in Science - 2013
Temporal variation in oviposition activity of Aedes aegypti mosquitoes in the Sonoran desert region and dengue transmission risk
Tracking the Culprit Carrying Dengue Fever
Robin Rathman, a biology teacher at Cienega High School in Vail, Arizona, is participating in a study of the Aedes aegypti mosquito, the principal vector of dengue fever, a serious viral disease that affects close to half the human population.
“My role is to look at the egg-laying behavior of Aedes aegypti in Tucson and note activity over time,” Rathman said. “It’s part of a larger study to see how mosquito egg-laying activity might be tied in with climate.
The two-year study (2014-2015) is being done under the direction of Assistant Professor Kathleen Walker, University of Arizona department of entomology.
Rathman is trapping, rearing and identifying mosquitoes on a weekly basis from February through November in Tucson, where dengue is absent. Meanwhile, additional trapping takes place in Nogales, Sonora, Mexico, where the disease is also absent, and Hermosillo, Sonora, where dengue is present. The cities run along a north/south alignment, with fairly hot and dry conditions in the north (Tucson) and hotter, more humid conditions in the south (Hermosillo).
“In Tucson we have the mosquito and no dengue. The question is why,” Rathman said. “Is there something different about the mosquitoes in Hermosillo versus the ones in Nogales, versus the ones in Tucson?”
One possibility that Walker’s research group has already figured out is that the Hermosillo mosquitoes seem to live longer than Tucson mosquitoes.
“So Tucson represents a pretty harsh environment for them,” Rathman said. “They have to live for 12 days after they bite a person with dengue in order for the virus to make more progress. We’ve found mosquitoes in Tucson aren’t living for the 12 days, and so they’re not able to transmit the dengue.”
Researchers pull the mosquitoes abdomens apart and examine the ovaries under a microscope, Rathman said. “You can tell how old the mosquitoes are from the structure of the ovaries.” The presence of certain proteins also reveal a mosquito’s age, she said.
Rathman has set six mosquito traps in central and southeast Tucson. “Basically they contain stinky water, produced by a hay infusion, to attract mosquitoes. The bugs lay their tiny eggs on the traps’ damp paper. Rathman collects the papers once a week and, using a magnifying glass, carefully counts the eggs. During one week in August she counted as many as 300 eggs on a paper. Then she allows them to hatch to verify that they are Aedes aegypti.
Her students are interested in this project, Rathman said.
“Some of them get very excited and they come and tell me, ‘I had a mosquito laying on me yesterday. Am I going to get dengue fever?’ She reminds that that the disease isn’t present in Tucson – yet. A changing climate could alter that happy circumstance.
“A few of my students who have lived in Mexico have had dengue, so they can tell us what it’s like,” she said. “It’s horrible. It feels like your bones are breaking. And you get all this pressure behind your eyes. You get fever and it’s really bad.”
She noted there are four serotypes of the dengue virus. “And if you get it again a second or third time, chances are higher that you might get hemorrhagic fever, and that’s fatal.”