But major obstacles remain before 'malaria-proof' is released from lab

Art Chimes | St. Louis, Missouri 19 July 2010
 

Photo: M. Riehle, University of Arizona
Under UV light, this mosquito larva reveals a red fluorescent marker in its nervous system, causing eyes and nerves to glow. The marker's presence tells the researchers in Riehle's team that this individual carries the genetic construct rendering it immune to the malaria parasite.

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PloS Pathogens

Malaria kills about a million people each year, mostly children in Africa.

Efforts to combat the disease have centered on controlling the mosquito that transmits the malaria parasite. Bed nets and eradication programs have had success, but now a team of U.S. researchers is trying a different approach — a genetically modified mosquito that can not transmit the disease.

University of Arizona scientist Michael Riehle explains that as the malaria parasite reproduces inside the mosquito, there is one part of the parasite's life cycle when it is particularly vulnerable.

"We're targeting the malaria parasites as they travel across the midgut," he explained. "And we chose that because that's the stage where the fewest number of malaria parasites are present."

Only a few dozen of the plasmodium parasites, in fact. Unless they're stopped, they would eventually multiply in the thousands to infect the next person bit by the mosquito.

Riehle Lab, University of Arizona
Michael Riehle, holding genetically altered mosquitoes, and his team work in a highly secure lab environment to prevent genetically altered mosquitoes from escaping.

So Riehle and his colleagues developed a genetic modification that disrupts some key functions in the mosquito, including its immune response and lifespan. The modified mosquitoes die sooner, meaning they have less time to bite a new victim and transmit malaria. More importantly, the genetic changes kill the parasites in the midgut.

But Riehle admits, they don't know exactly why.

"One of the things we want to know is definitely how this is working. We have some ideas as to how the parasite's being killed, but we really don't know at this point. And so future studies are going to figure out what exactly this gene is doing in there to kill the malaria parasite. And that should help us generate an even more effective malaria-proof mosquito."

If they succeed, a malaria-proof mosquito could be a powerful weapon in the fight against a killer disease — assuming it can actually be deployed.

Riehle says the engineered mosquito would have to be further modified to displace the mosquitoes that carry malaria.

"And the idea is, you give the mosquitoes some sort of mechanism that gives them a competitive advantage in the wild. Therefore, when you release them, the mosquitoes can out-compete the wild mosquitoes, and over time, over a period of several years, actually replace the population."

Creating a genetically-modified mosquito to prevent malaria transmission is one thing; modifying it to drive the existing mosquitoes to extinction may be another. And University of Arizona scientist Michael Riehle admits there are, as he put it, "a number of hurdles" to overcome. In any event, he says it will be at least 10 years before the genetically modified mosquitoes might be ready to leave the lab.

He describes this novel way of preventing the spread of malaria in the journal PloS Pathogens.