Diversity, composition, altitude, and seasonality of high-altitude windborne migrating mosquitoes in the Sahel: Implications for disease transmission

Recent studies have reported Anopheles mosquitoes captured at high-altitude (40–290 m above ground) in the Sahel. Here, we describe this migration modality across genera and species of African Culicidae and examine its implications for disease transmission and control. As well as Anopheles, six other genera—Culex, Aedes, Mansonia, Mimomyia, Lutzia, and Eretmapodites comprised 90% of the 2,340 mosquitoes captured at altitude. Of the 50 molecularly confirmed species (N = 2,107), 33 species represented by multiple specimens were conservatively considered high-altitude windborne migrants, suggesting it is a common migration modality in mosquitoes (31–47% of the known species in Mali), and especially in Culex (45−59%). Overall species abundance varied between 2 and 710 specimens/species (in Ae. vittatus and Cx. perexiguus, respectively). At altitude, females outnumbered males 6:1, and 93% of the females have taken at least one blood meal on a vertebrate host prior to their departure. Most taxa were more common at higher sampling altitudes, indicating that total abundance and diversity are underestimated. High-altitude flight activity was concentrated between June and November coinciding with availability of surface waters and peak disease transmission by mosquitoes. These hallmarks of windborne mosquito migration bolster their role as carriers of mosquito-borne pathogens (MBPs). Screening 921 mosquitoes using pan-Plasmodium assays revealed that thoracic infection rate in these high-altitude migrants was 2.4%, providing a proof of concept that vertebrate pathogens are transported by windborne mosquitoes at altitude. Fourteen of the 33 windborne mosquito species had been reported as vectors to 25 MBPs in West Africa, which represent 32% of the MBPs known in that region and include those that inflict the heaviest burden on human and animal health, such as malaria, yellow fever, dengue, and Rift Valley fever. We highlight five arboviruses that are most likely affected by windborne mosquitoes in West Africa: Rift Valley fever, O'nyong'nyong, Ngari, Pangola, and Ndumu. We conclude that the study of windborne spread of diseases by migrating insects and the development of surveillance to map the sources, routes, and destinations of vectors and pathogens is key to understand, predict, and mitigate existing and new threats of public health

Windborne long-distance migration of malaria mosquitoes in the Sahel

Over the past two decades efforts to control malaria have halved the number of cases globally, yet burdens remain high in much of Africa and the elimination of malaria has not been achieved even in areas where extreme reductions have been sustained, such as South Africa1,2. Studies seeking to understand the paradoxical persistence of malaria in areas in which surface water is absent for 3–8 months of the year have suggested that some species of Anopheles mosquito use long-distance migration3. Here we confirm this hypothesis through aerial sampling of mosquitoes at 40–290 m above ground level and provide—to our knowledge—the first evidence of windborne migration of African malaria vectors, and consequently of the pathogens that they transmit. Ten species, including the primary malaria vector Anopheles coluzzii, were identified among 235 anopheline mosquitoes that were captured during 617 nocturnal aerial collections in the Sahel of Mali. Notably, females accounted for more than 80% of all of the mosquitoes that we collected. Of these, 90% had taken a blood meal before their migration, which implies that pathogens are probably transported over long distances by migrating females. The likelihood of capturing Anopheles species increased with altitude (the height of the sampling panel above ground level) and during the wet seasons, but variation between years and localities was minimal. Simulated trajectories of mosquito flights indicated that there would be mean nightly displacements of up to 300 km for 9-h flight durations. Annually, the estimated numbers of mosquitoes at altitude that cross a 100-km line perpendicular to the prevailing wind direction included 81,000 Anopheles gambiae sensu stricto, 6 million A. coluzzii and 44 million Anopheles squamosus. These results provide compelling evidence that millions of malaria vectors that have previously fed on blood frequently migrate over hundreds of kilometres, and thus almost certainly spread malaria over these distances. The successful elimination of malaria may therefore depend on whether the sources of migrant vectors can be identified and controlled

VARIATION SAISONNIERE DES ARTHROPODES DINTERET MEDICAL, VETERINAIRE ET AGRICOLE DANS DIFFERENTES ZONES ECO-CLIMATIQUES DU MALI

Introduction: Les Arthropodes sont vecteurs de nombreuses maladies chez les hommes, les animaux et les plantes. Cest pourquoi lidentification des vecteurs devient necessaire afin de mener une lutte a travers des programmes nationaux de lutte. Methodes: Cette etude a ete conduite dans trois differentes zones eco-climatiques du Mali afin de voir la variation saisonniere des Arthropodes dinteret medical, veterinaire et Agricole au Mali. La collecte des arthropodes a ete faite a laide de deux types de piege (Piege demergence et piege en T) dans les villages de Bia, de Kenieroba et de Thierola. Les identifications ont ete faites a la loupe pour les Arthropodes, et par PCR pour les moustiques. Limportance des Arthropodes collectes a ete evaluee a travers leur dominance et leur frequence en fonction des zones et des saisons. Resultats: Letude des arthropodes des trois zones a permis davoir un apercu de lensemble de variations qualitatives et quantitatives des differents Arthropodes. Un total de 20 especes dArthropodes appartenant a trois classes a ete identifie (Arachnides, Insectes Myriapodes), 13 ordres (Araneides, Coleopteres, Dermapteres, Dictyopteres, Dipteres, Hemipteres, Hymenopteres, Lepidopteres, Nevropteres, Odonates, Orthopteres, Plecopteres, Trichopteres). Les Dipteres sont mieux representes a Bia et a Thierola et les Coleopteres frequents a Kenieroba. Conclusion: Il ressort de cette etude que les Arthropodes etaient plus frequents pendant la saison des pluies sur les sites. Les Arthropodes dinteret agricole constituaient le groupe dominant sur chacun des sites, suivi de ceux dinteret medical

Data from: Marking mosquitoes in their natural larval sites using 2H-enriched water: a promising approach for tracking over extended temporal and spatial scales

1. Background. Tracking mosquitoes using current methods of mark-release-recapture are limited to small spatial and temporal scales exposing major gaps in understanding long-range movements and extended survival. Novel approaches to track mosquitoes may yield fresh insights into their biology which improves intervention activities to reduce disease transmission. Stable isotope enrichment of natural mosquito breeding sites allows large-scale marking of wild mosquitoes absent human handling. Mosquito larvae that develop in 2H-enriched water are expected to be detectable for over four months using tissue mass-fraction 2H measurements, providing opportunities for long-term mark-capture studies on a large scale. 2. Approach. A laboratory study followed by a field experiment of mosquito larval habitat 2H-enrichment was conducted in Mali, to evaluate potential labeling of wild mosquitoes. Twelve natural larval sites were enriched using [2H]-Deuterium-oxide (D2O, 99%). Enrichment level was maintained by supplementation following dilution by rains. Availability of 2H to mosquito larvae was enhanced by locally collected and cultured microorganisms (i.e. protozoa, algae and bacteria) reared in deuterated water, and provided as larval diet. Putative natural predators were removed from the larval sites and first instar larvae Anopheles gambiae s.l. larvae were added every other day. Emergence traps enabled collection of eclosing adults. Adult mosquitoes were kept at laboratory conditions for analysis of label attrition with age. 3. Results. Deuterium enrichment of wild mosquitoes above background levels (maximum = 143.1 ppm) became apparent 5-6 days after initial exposure, after which 2H values increased steadily until ~24 days later (to a mean of approx. 220 ppm). Anopheles and Culex mosquitoes showed significantly different 2H values (211 and 194.2 ppm respectively). Both genera exhibited exponential label attrition (e(-x)) amounting to 21.6% by day 30 post emergence, after which attrition rate continuously decreased. Males of both taxa exhibited a higher mean 2H value compared to females. 4. Conclusions. Deuterium-oxide proved useful in marking mosquitoes in their natural larval sites and although costly, may prove valuable for studies of mosquitoes and other aquatic insects. Based on our field study, we provide a protocol for marking mosquito larval sites using deuterium-oxide

High SARS-CoV-2 Seroprevalence among Healthcare Workers in Bamako, Mali

In Mali, a country in West Africa, cumulative confirmed COVID-19 cases and deaths among healthcare workers (HCWs) remain enigmatically low, despite a series of waves, circulation of SARS-CoV-2 variants, the country’s weak healthcare system, and a general lack of adherence to public health mitigation measures. The goal of the study was to determine whether exposure is important by assessing the seroprevalence of anti-SARS-CoV-2 IgG antibodies in HCWs. The study was conducted between November 2020 and June 2021. HCWs in the major hospitals where COVID-19 cases were being cared for in the capital city, Bamako, Mali, were recruited. During the study period, vaccinations were not yet available. The ELISA of the IgG against the spike protein was optimized and quantitatively measured. A total of 240 HCWs were enrolled in the study, of which seropositivity was observed in 147 cases (61.8%). A continuous increase in the seropositivity was observed, over time, during the study period, from 50% at the beginning to 70% at the end of the study. HCWs who provided direct care to COVID-19 patients and were potentially highly exposed did not have the highest seropositivity rate. Vulnerable HCWs with comorbidities such as obesity, diabetes, and asthma had even higher seropositivity rates at 77.8%, 75.0%, and 66.7%, respectively. Overall, HCWs had high SARS-CoV-2 seroprevalence, likely reflecting a “herd” immunity level, which could be protective at some degrees. These data suggest that the low number of cases and deaths among HCWs in Mali is not due to a lack of occupational exposure to the virus but rather related to other factors that need to be investigated