The largest genetic study of mosquitoes has found their ability to resist insecticides is evolving rapidly and spreading across Africa, putting millions of people at higher risk of contracting malaria.

British scientists who led the work said mosquitoes' growing resistance to control tools such as insecticide-treated bed nets and insecticide spraying, which have helped cut malaria cases since 2000, now threatens "to derail malaria control" in Africa.

"Our study highlights the severe challenges facing public efforts to control mosquitoes and to manage and limit insecticide resistance," said Martin Donnelly of the Liverpool School of Tropical Medicine, who worked on the study with a team from Britain's Wellcome Trust Sanger Institute.