Building Better Mosquitoes

Sunday, September 01, 1996
Most efforts to combat such mosquito-borne diseases as malaria and dengue have focused on either vaccinating humans or wiping out mosquitoes with pesticides. Unfortunately, both methods have been only partially successful. We’re almost running out of options, says virologist Ken Olson of the Arthropod-Borne and Infectious Diseases Laboratory at Colorado State University. The spread of these diseases is increasing, control of mosquito populations is very lax worldwide, and mosquitoes are becoming pesticide resistant. That’s why Olson and his colleagues are taking a novel approach to disease control. They’re vaccinating mosquitoes, not people, making them resistant to dengue and thus incapable of infecting humans.

Dengue is a viral disease transmitted through mosquito saliva. And like most mosquito-borne viruses, the dengue virus carries its genetic information in the form of rna. So Olson decided to genetically engineer a stretch of rna that would bind to a complementary section of dengue rna that codes for a crucial viral protein.

He then inserted his creation into a Sindbis virus, a mosquito- borne virus that sometimes causes rashes and other minor symptoms in humans. His hope was that when the Sindbis virus replicated inside mosquito cells, it would produce copies of the engineered rna, which would bind to the rna of any dengue virus that was around. The altered rna would prevent the dengue from making a necessary protein, foiling the assembly of new viruses.

Olson injected both his doctored Sindbis viruses and dengue viruses into 26 Aedes aegypti mosquitoes, one of the two species that carry dengue. When he examined their saliva two weeks later, Olson found that all but one of the 26 mosquitoes were free of dengue. And the lone exception contained only a minute trace of the virus. Without dengue viruses in their saliva, says Olson, mosquitoes can’t transmit the disease to humans--and no other creature carries the virus. If you stop the ability of the mosquito to transmit to humans, says Olson, you’ll shut down dengue in nature.

Olson’s work is but a first step toward stopping the spread of dengue and other viruses. We’ve shown what we like to call proof of concept, says Olson. We can genetically alter a mosquito to where it will no longer transmit an important path-ogen. However, researchers still need to go beyond vaccinating mosquitoes to somehow integrating disease resistance into the genetic material of mosquitoes so they can pass their resistance to offspring. Olson believes that someone will solve the problem in the next decade. We wouldn’t be doing this research if we didn’t think it was ultimately practical, he says. Down the road, this could be a viable way of controlling disease transmission.
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