Windborne long-distance migration of malaria mosquitoes in the Sahel

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 even where extreme reductions have occurred over many years, such as in South Africa 1,2 . 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 migration 3 . 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 numbers of mosquitoes at altitude crossing a 100-km line perpendicular to the winds included 81,000 An. gambiae s.s., 6 million An. coluzzii, and 44 million An. squamosus. 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

Assessment of the probability of entry of Rift Valley fever virus into the EU through active or passive movement of vectors

“…Wind dispersal. A recent paper showed that wind dispersal of mosquitoes is possible (Huestis et al, 2019). In this study a maximum wind dispersal of 295 km was observed.…”

“…Most of the outbreaks reported to the OIE between 2006-2019 were located at a distance of more than 30 km from a large airport or port, which is beyond the active flight range of the RVF mosquito vectors (Figure 2, Figure 3, Appendix A). For the modelling of import through flights or ports we assumed that a mosquito can potentially be present at the premises of an airport or port introduced by wind from an outbreak located at a maximum distance of 295 km (Huestis et al, 2019) from the airport or port. The present document has been produced and adopted by the bodies identified above as author(s).…”

“…The green line indicates the maximum active flight range of the RVF mosquito vectors. The red line indicates the 295 km limit of wind dispersal observed in(Huestis et al, 2019).…”

Quantifying flight aptitude variation in wildA. gambiaes.l. in order to identify long-distance migrants

“…coluzzii and An. gambiae s.s., as well as several secondary malaria vectors regularly engage in seasonal flights 40-290 m above ground (Huestis et al 2019). Because of the large number of migrants, most of which were gravid females, and the large distances they were able to cover, the likely epidemiological significance of such movements was inescapable.…”

“…However, recent aerial sampling data (Huestis et al 2019) has led us to modify the latter prediction, to suggest the presence of migrants across the three species. The data from the aerial sampling study (Huestis et al 2019) also led us to modify our initial prediction reflecting the high frequency of gravid females in altitude. Finally, we investigated whether putative migrants (based on our flight mill data) exhibit different wing morphology.…”