April 2, 2013, 6:24 p.m.
A surprising research discovery in mosquitoes could affect future prospects for malaria control. A team of scientists from West Africa, the United States and the United Kingdom found that the mosquito, Anopheles gambiae, which was thought to be splitting into two completely new species, may actually have a more complex range of forms due to frequent inter-mating. The resulting hybrids may have implications for insecticide resistance and malaria parasite infectivity.
The study published in the April 2013 issue of the journal Genetics, documents substantial amounts of hybridization among two separate mosquito types in a large area spanning four countries in sub-Saharan western Africa.
"Our research shows that Anopheles gambiae mosquitoes, which are responsible for most cases of malaria in Africa, are more genetically complex than we thought due to interbreeding," said David J. Conway, Ph.D., one of the researchers from the London School of Hygiene & Tropical Medicine in the United Kingdom, and the Medical Research Council Unit in The Gambia. "Mosquitoes are very good at evolving quickly and this information will help us use existing control methods appropriately and consider possible new tools that will further malaria control efforts in Africa."
The scientists collected mosquitoes from houses located within 100 kilometers of the Atlantic coast in Senegal, Gambia, Guinea Bissau, and Republic of Guinea. They characterized the mosquitoes' DNA to identify the proportions of each major type, "M," "S," and hybrid "M/S" forms. Pools of each of the forms of mosquitoes from representative sites were analyzed for genome-wide genetic profiles revealing that the genomes, which are known to be different between the forms, are not different in these areas. That is, the genetic variation that exists is shared between the forms, as if they were a single species.
"Mosquito-borne illnesses can be a death sentence in developing nations," said Mark Johnston, Editor-in-Chief of the journal Genetics. "It is crucial that we understand the genetic architecture of mosquito populations so we can develop ways to safeguard people from malaria. This research reveals some of the difficulty of eradicating this disease."
The genome-wide SNP array was supported by joint funding from several sources including Burroughs Wellcome Fund Request 1008238, the Broad Institute Director's Fund, Harvard School of Public Health Department of Immunology and Infectious Diseases under direction of D.F. Wirth, Wellcome Trust Programme Grant 077229/Z/05/Z to F.C. Kafatos and G.K. Christophides, and the DeLuca Professorship from Boston College to MATM. This work was enabled by funding from the UK Medical Research Council (MRC) and FNIH/Gates Grand Challenges in Global Health to the MRC Unit in The Gambia.