Updating Anopheles species and symbiont associations from the Sud Kivu Region of Eastern Democratic Republic of Congo
This study updates the understanding of Anopheles species diversity and symbiont associations in Sud Kivu, Eastern DRC, by revealing seasonal shifts between An. gambiae and An. demeilloni populations, confirming the presence of An. maculipalpis and An. coustani s.l., and demonstrating that while An. gambiae lacks malaria-inhibiting symbionts, An. demeilloni harbors high prevalence of Wolbachia.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Malaria remains one of the most persistent threats to human health, a disease carried by mosquitoes that kills hundreds of thousands of people every year. In the Democratic Republic of Congo, the second highest number of cases in the world, the challenge is compounded by political instability and difficult terrain, making it hard for scientists to track exactly which mosquitoes are present and how they behave. To fight this disease effectively, researchers must know the specific identity of the insects they are studying, as different species have different habits and play different roles in spreading the illness. Beyond just naming the mosquitoes, scientists are increasingly interested in the tiny organisms living inside them. Some bacteria and fungi, known as symbionts, can naturally stop a mosquito from transmitting malaria. If these microscopic allies can be understood and perhaps encouraged to spread through wild mosquito populations, they could become powerful tools to reduce the disease without relying solely on chemical sprays.
In the high-altitude villages of the Sud Kivu region in eastern Congo, a team of researchers set out to update the map of mosquito life and check for these helpful microscopic partners. The area is home to a complex mix of mosquito species, but previous records were often based on simple visual checks that could miss subtle differences between closely related insects. The team conducted two separate surveys, one spanning nearly a year from late 2021 to late 2022, and another in the summer of 2023. They collected adult mosquitoes from six different sites, using light traps and hand-held aspirators to catch them inside homes and the surrounding environment. Once captured, the insects were brought to a local laboratory for initial sorting, and then sent to the United Kingdom for detailed genetic analysis to confirm their exact species and to screen them for the presence of Wolbachia bacteria and Microsporidia MB, two types of symbionts known to interfere with malaria transmission.
The results revealed a striking shift in the mosquito population depending on the time of year. During the first survey, which covered the wetter months, the vast majority of the mosquitoes collected belonged to the Anopheles gambiae group, a primary driver of malaria transmission. Genetic testing confirmed that these were specifically the Anopheles gambiae species, with no evidence of their close relative, Anopheles coluzzii, in this part of the country. Crucially, when the researchers tested these mosquitoes for the helpful symbionts, they found nothing; the mosquitoes were completely free of both Wolbachia and Microsporidia MB. This suggests that in this specific region and during this season, the main malaria vectors do not naturally carry these protective microbes.
The picture changed dramatically when the team returned in August 2023, during a drier period. Instead of the malaria-transmitting species, the traps were filled with a different mosquito called Anopheles demeilloni. This species, which prefers semi-permanent water sources like streams that remain even when the rain stops, made up most of the catch. When the researchers tested these mosquitoes, they found a high prevalence of Wolbachia bacteria. In one village, nearly three-quarters of the Anopheles demeilloni mosquitoes carried the bacteria, while in a neighboring village, about one-third were infected. This finding is significant because it confirms that this specific mosquito species naturally hosts a stable, high-density infection of Wolbachia, which has the potential to spread through the population and block malaria transmission. The researchers also identified other less common species in the 2023 collection, including Anopheles maculipalpis and Anopheles coustani, confirming their presence in the region. Interestingly, while the team noticed variations in the wing patterns of the Anopheles coustani mosquitoes, genetic testing showed they were all the same species, highlighting how difficult it can be to tell these insects apart just by looking at them.
The study concludes that the landscape of malaria risk in eastern Congo is not static but changes with the seasons, with different mosquito species dominating at different times of the year. While the primary malaria vectors found in the wet season do not carry the protective bacteria, the presence of Wolbachia in the abundant Anopheles demeilloni during the dry season offers a natural example of how these microbes can thrive in wild populations. The researchers found no evidence of the other symbiont, Microsporidia MB, in any of the mosquitoes they tested, nor did they find any other strains of Wolbachia besides the one already known to infect Anopheles demeilloni. These findings provide a clearer, more accurate picture of the insect world in this region, showing that effective malaria control strategies must account for seasonal changes in mosquito populations and the specific biological traits of each species.
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