Puzzling Mosquito May Complicate Malaria Control

A newly discovered species of mosquito may complicate malaria-control efforts in parts of Africa. Researchers have identified an insect that looks nearly identical to a species that carries the disease, yet that may or may not transmit malaria. If ongoing studies find that the mosquito does not carry the malaria parasite, vector-control teams could waste valuable resources, including insecticides and bed nets, fighting a harmless insect.

Africa is home to at least 140 species of Anopheles mosquitoes. But only seven species are known to transmit the malaria parasite to humans, including members of the An. funestus and An. gambiae groups.

"Confusers." These mosquito larvae from Malawi belong to a new Anopheles species

A South African field team found the new mosquito species inside reed huts in rural villages in the malaria-prone nation of Malawi. Although it looked just like the vector An. funestus, genetic testing revealed that it did not match any of the known Anopheles species. So far, no specimens of the new species have been found with the malaria parasite. "If this mosquito is not a malaria vector, it is certainly a 'confuser'--looking exactly like one of the major vectors," says medical entomologist Richard Hunt, a member of the team that reports its finding this month in theAmerican Journal of Tropical Medicine and Hygiene.

And that could exacerbate vector-control efforts in Malawi, says study co-author Maureen Coetzee, who directs the medical entomology research unit at the University of the Witwatersrand in Johannesburg, South Africa. "Malaria-control resources are limited, and it would be a waste of money to kill off a mosquito species that may look exactly like a malaria vector but is not," she says. "Malawi may have to invest in a basic molecular laboratory to tell the difference."

The finding "explains a number of the rather strange results we were getting" in trying to identify mosquito species in Malawi using routine polymerase chain reaction assays, says insect molecular biologist Janet Hemingway, director of the Liverpool School of Tropical Medicine in the U.K., who was not involved in the study.

"It's more than a little depressing that after a century of work, we still seem not to know how many species there are in the funestus group, let alone how good each is at transmitting malaria," adds evolutionary biologist Andrew Read of Pennsylvania State University, University Park, who studies the evolutionary genetics of malaria and its vectors.

Indeed, Coetzee says there are likely many more Anopheles species in relatively unexamined regions of Africa such as the Democratic Republic of the Congo: "There is still an awful lot we don't know."

REFERENCE: http://sciencenow.sciencemag.org/cgi/content/full/2009/902/3?etoc