Tucson: UA Research Targets Mosquito-Borne Illnesses

Genetics vs. bug-borne illness

By Otto Ross

ARIZONA DAILY STAR 11/12/09

Genetically engineered mos­quitoes created by UA entomol­ogists could provide a valuable weapon against malaria, dengue, West Nile and other mosquito-transmitted diseases. “We’re interested in under­standing the life span of mos­quitoes and trying to figure out ways to manipulate it for con­trolling mosquito-borne dis­eases,” said Michael Riehle, principal investigator of the project and an assistant profes­sor at the University of Arizona.

With more than a million an­nual deaths resulting from malaria, Riehle hopes that his project will be a first step in cre­ating a more effective method of fighting the disease.

“The tools we have to combat malaria right now are failing,” Riehle said. “The big things we have right now are insecticides to kill mosquitoes and drugs to kill the malaria parasites within people, and both have resist­ances developing to them. So a lot of the common insecticides and a lot of the common anti­malaria drugs are not effective.”

Riehle’s solution is to ap­proach the problem from within by genetically decreasing the life span of mosquitoes to the point that they won’t have time to develop diseases and become infectious. The average life span of a mosquito is about two weeks. This is also about the amount of time it takes for a mosquito to be able to transmit malaria and other diseases to humans. For this reason, a small reduction in a mosquito’s life span could have dramatic ef­fects, said Vanessa Corby-Har­ris, a postdoctoral student who works in Riehle’s lab.

“Even just a reduction of one day would make a big differ­ence,” she said. “If we can just knock it down just that small amount, that’s what were inter­ested in doing.”

However, decreasing the life span of mosquitoes in the lab makes those insects less capable of competing with the unaltered type in nature. If the transgenic mosquitoes are to have any chance of replacing mosquitoes now found in the wild, the ento­mologists need to simultaneously increase their reproduction rate to compensate for their shorter lives. The team hopes to achieve both of these goals by genetical­ly manipulating insulin signal­ing cascades within the mos­quitoes. The signaling cascades are usually activated when in­sulin is secreted within the mosquito and are involved in a variety of functions, including metabolism, growth and repro­duction. Overstimulating the cascade seems to reduce the life span of mosquitoes and in­crease the reproduction rate. Inversely, inhibiting the cascade typically lengthens life span and decreases reproduction rate.

The research team recently won a $100,000, one-year Grand Challenges Exploration grant from the Bill and Melinda Gates Foundation to prove this in a lab. The grant is aimed at funding high-risk, high-reward projects such as Riehle’s.

There is a risk that the needed decrease in life span and in­crease in reproduction can’t be achieved, Riehle said.

“But if it does pan out as good as we hope or better, it has a chance to — I’m hesitant to say ‘eliminate malaria’ — but it could be a major tool in our tool chest to combat malaria.”

If the project is successful, Riehle will apply for a two-year grant extension of up to $1 mil­lion. The next stage in the proj­ect would involve building larg­er enclosures to continue to study life span and also begin introducing genetically modi­fied mosquitoes into a group of wild mosquitoes in a controlled environment.

Contact reporter Otto Ross at 573-4125 or oross@azstarnet.com