Wind-borne mosquitoes carry infectious pathogens over hundreds of miles

Wind-borne mosquitoes carry infectious pathogens over hundreds of miles

Balloon sampling has now confirmed that mosquitoes migrating high over West Africa often carry transmissible pathogens, a finding that could change the way we track and combat vector-borne diseases.

Study: Pathogens are spread by high-flying wind flies. Image credit: Shutterstock AI/Shutterstock.com

In a recent study inPNASResearchers tested whether mosquitoes that migrate to high altitudes carry infectious pathogens.

They found that high-flying mosquitoes were often infected with 21 mosquito-borne pathogens and were often already infectious. These included West Nile virus, dengue fever, several avian Plasmodium species and several filarial nematodes.

High-altitude mosquito flights continued to pose an unproven threat

Wind-borne long-distance migration of insects is a well-known phenomenon, often extending hundreds of kilometers in a single night and involving large amounts of biomass. Mosquitoes and other insects that act as vectors, pests or beneficial insects are known to participate in these flights.

However, there remain large gaps in our knowledge regarding the ecological and epidemiological impacts of these migrations, particularly for tropical mosquitoes. Previous research has shown that mosquitoes can travel to high altitudes and spread pathogens over long distances. However, this hypothesis relies primarily on indirect meteorological or epidemiological correlations rather than direct detection of infected mosquitoes in the air column.

Recent African field studies have shown that many mosquito species regularly fly between 40 and 290 m above the ground, often during disease transmission season. These migrants are dominated by gravid females that fed on vertebrates, suggesting they were previously exposed to pathogens. Many of these species are considered vectors of viruses, protozoa, or helminths, raising the possibility that infectious mosquitoes may be transported to new areas by winds at higher elevations.

DNA barcoding revealed 61 species in elevation

The researchers collected mosquitoes using nets suspended from helium balloons positioned between 120 and 290 m above the ground in Ghana and Mali. Sampling took place on 191 nights between 2018 and 2020.

A total of 1,247 mosquitoes were captured, of which 1,017 female specimens were examined for infections. Species identification was achieved using mitochondrial cytochrome c oxidase subunit I (COI) barcode sequencing, allowing classification into 61 species in 10 genera.

To detect infection, the team conducted cross-genus polymerase chain reaction (PCR) tests targeting the major groups of mosquito-borne pathogens: flaviviruses, alphaviruses, Plasmodium spp. and filarial nematodes.

Both abdominal and head-thoracic tissues were tested to distinguish mere exposure (pathogen genetic material in the abdomen from a blood meal) from disseminated infection (pathogen present in the thorax, indicating spread beyond the gut and possible transmission competence). When dissection was not possible, whole body samples were used.

Positive samples were subjected to Sanger sequencing or metagenomic analysis to confirm pathogen identity and detect additional viruses or parasites. Infection prevalence was assessed overall and by species. The study also assessed co-infection patterns and compared abdominal and thoracic infection rates to infer likely vector competence and transmission potential during or after long-distance migration.

Every eighth mosquito carried at least one pathogen

High altitude sampling revealed a diverse assemblage of mosquito species dominated by Culex, Aedes and Anopheles. Of the 994 mosquitoes identified as species, 61 different species were represented, including known vectors of malaria and arboviruses. The majority were women, and almost half were pregnant, reflecting previous blood feeding and an increased likelihood of exposure to pathogens.

The pathogen screening revealed significant infection rates. Overall, 8% of mosquitoes tested positive for Plasmodium species, 3.5% for flaviviruses and 1.6% for nematodes. As expected, abdominal infections were more common than head and thorax infections, but disseminated infections (indicating likely transmissibility) were found in several species. Approximately 6.3% of mosquitoes transmit disseminated infections of all pathogen groups, including several dominant high mountain species.

A total of 21 vertebrate-infecting pathogens were detected. These included 15 avian Plasmodium species, West Nile virus, Orthobunyavirus M'Poko virus, dengue virus (PCR detectable but not sequence confirmed) and three nematodes. Nineteen of the 21 detected pathogens were associated primarily with wild birds or forest hosts, suggesting that high-altitude mosquito transmission may be particularly relevant to pathogen cycles in wildlife.

Remarkably, coinfection patterns did not deviate from random expectations. Overall, 12.7% of mosquitoes carried at least one pathogen and 15 species had disseminated infections, suggesting possible transmissibility.

Airborne mosquitoes could spread disease across regions

This study provides the first direct evidence that mosquitoes migrating to high altitudes often carry multiple vertebrate pathogens, and a smaller but significant proportion are already infective with them. These results support long-standing but previously unproven hypotheses that windborne migration of mosquitoes contributes to the long-distance spread of pathogens.

Evidence of disseminated infections in dominant aerial species suggests that long-range movement may help maintain forest cycles and generate new outbreaks far from original host populations.

Strengths of this analysis include large-scale, multi-year air sampling; molecular pathogen screening across multiple taxonomic groups; and confirmation by sequencing or metagenomics. Limitations include the modest sample sizes for some species, the inability to assess true transmission after landing, and the exclusion of some pathogen groups.

Nevertheless, the evidence strongly suggests that high-altitude mosquito traffic represents an underappreciated component of pathogen ecology. Because most detected pathogens were sylvatic pathogens, this mechanism may play a greater role in the spread of wild pathogens than in the direct transmission of human disease, although the possibility of spillover transmission remains. The study concludes that incorporating aerial mosquito migration into surveillance and control strategies is critical to understanding and managing vector-borne disease risks.

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