A hybrid "super mosquito" that is resistant to the insecticide used to treat life-saving anti-malaria bed nets has emerged in Mali as a result of the interbreeding of two species of malaria mosquito.
Gregory Lanzaro, medical entomologist and professor at University of California Davis (UC Davis) and leader of the research team behind the discovery, says they are calling the hybrid mosquito a "super" mosquito because it can survive exposure to the insecticides used to treat bed nets.
He and his team report their findings in the Proceedings of the National Academy of Sciences.
Prof. Lanzaro says the study provides convincing evidence that a man-made change - namely the introduction of insecticides - into the environment of the malaria-carrying mosquitoes altered their evolutionary relationship and broke down the "reproductive isolation that separates them."
"What we provide in this new paper is an example of one unusual mechanism that has promoted the rapid evolution of insecticide resistance in one of the major malaria mosquito species," adds Prof. Lanzaro, who is also Director of the Vector Genetics Laboratory at UC Davis.
'Adaptive introgression' coincided with increased use of insecticide-treated bed nets
The super-mosquito that Prof. Lanzaro and colleagues identified is a hybrid of two malaria-carrying mosquitoes - Anopheles gambiae and Anopheles coluzzii. Previously, entomologists thought these two mosquitoes were different forms of A. gambiae, but now they are recognized as separate species.
In their study, Prof. Lanzaro and colleagues describe how the hybrid emerged when a type of gene-swapping called "adaptive introgression" occurred at the same time as increased usage of insecticide-treated bed nets.
Malaria is a potentially life-threatening disease caused by the Plasmodium parasite, which enters the human bloodstream via the bite of an infected mosquito. In the human body, the parasite multiplies in the liver and then infects red blood cells. If not treated, malaria disrupts blood supply to vital organs and can eventually lead to death.
Malaria kills hundreds of thousands of people every year, most of them sub-Saharan children under the age of 5.
Key anti-malaria control methods include prompt and effective treatment, use of insecticide nets and indoor spraying with insecticides.
Prof. Lanzaro says insecticide-treated nets have made a significant contribution in the global fight against malaria, and credits them with saving thousands, probably tens of thousands of lives in Mali alone.
But he says he and his team were not surprised to find insecticide resistance in the malaria mosquito. They and other scientists have been watching it grow for some time.
"Recently," he adds, "it has reached a level at some localities in Africa where it is resulting in the failure of the nets to provide meaningful control, and it is my opinion that this will increase."
Urgent need for new malaria control strategies
There is a pressing need for new malaria control strategies, urges Prof. Lanzaro.
Different types of malaria control are in development. Recently, Medical News Today reported how researchers have developed a fast-acting anti-malaria compound that removes all traces of malaria parasite in mice within 48 hours.
Other anti-malaria insecticides are also in development, as are biological agents that use bacteria and fungi to kill mosquitoes, and genetic treatments that alter mosquito genes to either kill them or remove their ability to pass on malaria.
The World Health Organization (WHO) say thanks to increased disease control, deaths to malaria have fallen dramatically worldwide, and new cases are falling steadily. Also, more and more countries are moving toward eliminating malaria altogether. In its 2014 report, WHO show how global malaria deaths fell by 47% between 2000 and 2013.
Meanwhile, we recently learned of another study that sheds light on how mosquitoes transmit malaria. Writing in Science Express, the international team describes how it sequenced the genomes of 16 species of Anopheles mosquito to provide new clues on how they adapt to humans as primary hosts of malaria.