Windborne long-distance migration of malaria mosquitoes in the Sahel

Authors: HUESTIS, DIANA - Nih, National Institutes Of Allergy And Infectious Diseases; DAO, ADAMA - University Of Bamako; DIALLO, MOUSSA - University Of Bamako; SANOGO, ZANA LAMISSA - University Of Bamako; SAMAKE, DIJIBRIL - University Of Bamako; YARO, SEYDOU - University Of Bamako; OUSMAN, YOSSI - University Of Bamako; LINTON, YVONNE-MARIE - Walter Reed Army Medical Center; KRISHNA, A. - National Instiute Of Allergy And Infectious Diseases (NIAID, NIH); VERU, LAURA - National Instiute Of Allergy And Infectious Diseases (NIAID, NIH); KRAJACIC, BENJAMIN - National Instiute Of Allergy And Infectious Diseases (NIAID, NIH); FAIMAN, R. - National Instiute Of Allergy And Infectious Diseases (NIAID, NIH); FLORIO, JENNA - National Instiute Of Allergy And Infectious Diseases (NIAID, NIH); CHAPMAN, JASCON - Rothamsted Research; REYNOLDS, DON - University Of Greenwich; WEETMAN, DAVID - Liverpool School Of Tropical Medicine; MITCHELL, R. - Smithsonian Institute; DONNELLY, MARTIN - University Of Kwazulu-Natal; TALAMAS, E. - University Of Kwazulu-Natal; Chamorro, Maria; STROBACH, UDI - University Of Maryland; LEHMANN, TOVI - National Instiute Of Allergy And Infectious Diseases (NIAID, NIH)

Submitted to: Nature
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2019
Publication Date: 10/1/2019
Citation: Huestis, D., Dao, A., Diallo, M., Sanogo, Z., Samake, D., Yaro, S.A., Ousman, Y., Linton, Y., Krishna, A., Veru, L., Krajacic, B., Faiman, R., Florio, J., Chapman, J., Reynolds, D., Weetman, D., Mitchell, R., Donnelly, M., Talamas, E., Chamorro, M.L., Strobach, U., Lehmann, T. 2019. Windborne long-distance migration of malaria mosquitoes in the Sahel. Nature. 28(4):6.

Interpretive Summary: Malaria, which is transmitted by mosquitoes, has not been eliminated and remains a significant health problem in Africa. The mosquitoes are able to persist in areas where surface water is absent for long periods of time during the year (between 3-8 months) and scientists have speculated that certain mosquitoes and other arthropods are undertaking long-distance migration. This study confirms this hypothesis by aerial sampling of mosquitoes and other arthropods 40-290 m above ground, providing the first evidence of long-distance movement by air of the primary vector of malaria in Africa, and as a result migration of the pathogen they transmit. An additional important finding was the species and sex of the mosquitoes sampled; the primary malaria vectors was sampled and 80% of the mosquitoes collected were females, of which 90% had taken a blood meal before migration. This implies that the pathogen will be transported long distances by the females. Based on the data, trajectories and estimates of total migrating numbers were calculated. Thus, results provide strong evidence that millions of previously blood-fed, malaria vectors frequently migrate over hundreds of kilometers, thus capable of spreading malaria over these distances. Malaria elimination success in Africa depends on whether sources of migrant vectors can be identified and controlled.

Technical Abstract: Over the past two decades, control efforts have halved malaria cases globally, yet burdens remain high in much of Africa and elimination has not been achieved. Studies seeking to understand the paradoxical persistence of malaria in areas where surface water is absent for 3–8 months of the year, suggested that certain Anopheles mosquitoes employ long-distance migration3. Here, we confirmed this hypothesis by aerial sampling of mosquitoes 40–290 m above ground, providing the first evidence of windborne migration of African malaria vectors, and consequently the pathogens they transmit. Ten species, including the primary malaria vector Anopheles coluzzii, were identified among 235 anophelines captured during 617 nocturnal aerial collections in the Sahel of Mali. Importantly, females accounted for >80% of all mosquitoes collected. Of these, 90% had taken a blood meal before their migration, implying that pathogens will be transported long distances by migrating females. The likelihood of capturing Anopheles species increased with altitude and during the wet seasons, but variation between years and localities was minimal. Simulated trajectories of mosquito flights indicated mean nightly displacements of up to 300 km for 9-hour flight durations. Annually, the estimated number of mosquitoes at altitude crossing a 100 km line perpendicular to the winds were 8.1x104, 6x106, and 4.4x107, for the vector species An. gambiae s.s., An. coluzzii, and An. squamosus, respectively. These results provide compelling evidence that millions of previously blood-fed, malaria vectors frequently migrate over hundreds of kilometers, and thus almost certainly spread malaria over such distances. Malaria elimination success may, therefore, depend on whether sources of migrant vectors can be identified and controlled.