Malaria is notoriously unpredictable. The increased number of cases in the Senegal study was observed over a single season (three to four months). I'm a little surprised they are being reported at this stage.
Malaria cases vary from month to month and year to year. Several seasons' data are needed before any firm conclusions can be drawn about trends.
It seems unlikely that use of insecticide-treated bed nets for two years would lead to a dramatic change in the population's level of immunity, or alone lead to a marked increase in resistance in mosquitoes.
The best way to prevent resistance would be not to use the drugs and insecticides at all. But this would deny half the world's population living at risk of malaria the tools estimated to have prevented 19 million cases of disease and 200,000 deaths in 2009 alone.
The Senegal study presents an interesting hypothesis which needs to be tested – but it should not dampen the vigour with which we pursue malaria control.
The writer is a professor at the London School of Hygiene and Tropical Medicine and an adviser to the charity Malaria No More