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Press Release | Nov. 13, 2019

Malarial Mosquitos Migrate Long Distances on High Level Wind Currents

Anopheles malaria vectors have been collected up to 290 meters up in the atmosphere, proving for the first time that they are able to undertake long-distance migrations, potentially spreading, introducing or re-introducing vector-borne diseases to their destinations. These findings, published in Nature, were collected by a global team, including scientists from the Walter Reed Biosystematics Unit, housed within the Smithsonian National Museum of Natural History, and part of the Walter Reed Army Institute of Research.

Though eradication efforts have made major progress, malaria remains a significant threat to public health and regional stability, particularly across Africa.  In regions with dry seasons, mosquito populations and disease transmission decrease dramatically; however, upon the first introduction of wide-spread standing water through rain, populations return dramatically.  Several theories for this repopulation phenomenon exist, including dormancy and migration from regions without dry seasons. 

This study, taking place across a nearly two-year period, collected hundreds of thousands of insects from sticky nets suspended from helium balloons at heights ranging from 40 to 290 meters above four villages in Mali’s Sahel region.  Of these insects, nearly 250 were Anopheles mosquitoes, including the major African malaria vectors Anopheles gambiae and An. coluzzii.  Critically, females (which bite and can transmit malaria) outnumbered males 4:1, and 90% were gravid (i.e. contained eggs), and therefore had taken at least one potentially infected blood meal < 36 hours before capture. Furthermore, and contrary to conventional views, it was demonstrated that these migrations regularly span tens to hundreds of kilometers per night. 

In essence, these findings argue that previously blood-fed, and therefore potentially infected, mosquitos travel significant distances, and that air-borne migration may be responsible for the introduction (or reintroduction) of malaria or other infectious diseases to the region – as is now thought to be the case during previous outbreaks in Israel and Egypt. 

Dr. Yvonne-Marie Linton, co-author of the Nature paper and research director of WRBU commented “That almost all the females collected were gravid is highly significant in terms of mosquito-borne disease transmission. As well as malaria-infected females being carried over long distances, some mosquito-borne viruses (e.g. West Nile virus) directly infect their offspring, meaning that infected females arrive gravid at their new destination ready to lay c.80-100 already infected eggs.”

These findings have significant impacts for control and elimination efforts for vector-borne disease; mosquito control efforts and vector hazard models will have to take long-distance migration into account.  WRAIR, WRBU and its partners remain committed to developing novel interventions to prevent the transmission of malaria, including mosquito repellents, chemoprophylaxis, biologics and more in order to eliminate this threat to Service Members deployed around the world.

More commentary from study authors is available here and here.