Malaria super–spreading mosquitoes can now be identified more easily. Researchers from the Institut Pasteur, CNRS and IRD, in collaboration with scientific teams from four African countries and the United States, have identified a genetic marker that helps detect malaria–susceptible mosquitoes which are more likely to be infected with Plasmodium parasites in the wild, thereby having greater chance to transmit the disease to humans. Called the 2La inversion, this marker is a frequent and geographically widespread genetic difference found in Anopheles gambiae mosquitoes, the major African malaria vector. Insects which carry this marker tend to spend more time outside, while most forms of malaria control target insects which are present indoors.

These results, published in the journal eLife on June 23rd, could lead to the development of new targeted strategies aimed at controlling vectors.

Researchers from the Institut Pasteur, CNRS and IRD, in collaboration with African and American scientists, have reported the existence of super–spreading mosquitoes in nature, which are particularly competent in transmitting the malaria parasite. Hence, thanks to this study, which was carried out in various villages of Guinea Conakry, Kenya and Burkina Faso, and which was led by Kenneth Vernick, head of the unit of Genetics and Genomics of Insect Vectors at Institut Pasteur, the scientists identified a genetic marker which is linked to a frequent and geographically widespread genetic difference that has large effect on malaria infection in mosquitoes – and, consequently, on an insect’s likelihood to transmit the disease. Named 2La, this marker is the first widespread genetic variation for malaria infection reported in the wild vector population.

The 2La genetic marker is a chromosome inversion. In Anopheles mosquitoes, this genetic variation is present in two forms: the 2La genetic sequence and the 2L+a genetic inversion. The study found that mosquitoes carrying the 2L+a genetic marker inversion (aka the susceptible marker) are twice as likely to be infected with malaria than mosquitoes carrying the other form (i.e. 2La).

The researchers also found a difference in mosquito behavior associated with the genetic marker: super–spreading mosquitoes, carrying the susceptible marker, spend more time outdoors compared to the other mosquitoes which tend to stay indoors.

These results indicate that, where abundant, especially in Central and East Africa, these mosquitoes may be responsible for a majority of malaria cases during the transmission season.

Considering that most efforts currently made in the fight against malaria vectors target both infected and non–infected mosquitoes equally as there is no easy way to distinguish between the two, and that they rely mainly on indoor directed control strategies like bed nets and insecticide spraying, these findings could open the door to the development of new vector controls targeting outdoor mosquitoes which, as this study showed, are also potent vectors of malaria.

The next steps include village–based studies of malaria mosquitoes in humid geographic zones of Africa, where the highest levels of human malaria occur, in order to confirm these results.