DNA marker reveals pyrethroid resistance in malaria mosquitoes

A new study, jointly led by Liverpool School of Tropical Medicine and the Centre for Research in Infectious Diseases (CRID) in Cameroon, has detected a DNA marker in a gene encoding for a key enzyme, known as cytochrome P450, that helps mosquitoes to break down and survive exposure to pyrethroids, the main insecticides used for treating bed nets.

This new finding, published in Science Translational Medicine, will help to better implement insecticide resistance management strategies and contribute to reducing the burden of malaria in sub-Saharan Africa, home to 90% of cases globally. 

Professor Charles Wondji, Professor of Genetics and Vector Biology at Liverpool School of Tropical Medicine and lead author on the study, said: "Our study designed field-applicable tools to easily track the spread of metabolic resistance in the major malaria mosquito species and assess its impact on control interventions. These important findings can help to maintain the effectiveness of insecticide-based tools such as bed nets which remain a cornerstone of malaria prevention."

Bed nets and indoor residual spraying have been critical to controlling the spread of malaria, but progress has slowed over the last decade because of increased insecticide resistance, notably through metabolic resistance processes in mosquitoes through the production of detoxification enzymes.

This growing global threat must be addressed to improve the effectiveness of current and future vector control strategies and further reduce the malaria burden, with 200 million cases and 600,000 deaths annually worldwide. 

Previous studies have identified genetic markers for other forms of resistance, but identifying DNA-based mechanisms in mosquitoes that cause metabolic resistance has proven more challenging.

This new research is the first to identify a DNA marker for metabolic pyrethroid resistance in West and Central African populations of Anopheles gambiae, one of the main malaria-carrying mosquito species.

Based on this marker, the researchers developed a reliable diagnostic test that will enable the detection and monitoring of pyrethroid resistance, the assessment of potential cross-resistance to new insecticides, and ultimately better inform choice of bed nets according to the genetic make-up of targeted mosquito populations.