Diversity, Distribution, and Plasmodium falciparum Sporozoite Infectivity of Anopheles Mosquitoes in Flood-Prone Communities of Kasese District, Western Uganda: A Cross- Sectional Household Entomological Study
This cross-sectional study in flood-prone communities of Kasese District, Uganda, reveals a diverse assemblage of Anopheles mosquito species and ongoing low-level Plasmodium falciparum transmission, highlighting the need for targeted vector control interventions in these climate-vulnerable areas.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
In the highlands of western Uganda, where deep river valleys cut through steep hills, the air carries a familiar and persistent threat: malaria. This disease, caused by a microscopic parasite, is transmitted to humans through the bite of specific mosquitoes. For decades, scientists have known that the environment shapes the lives of these insects. When it rains, water collects in temporary pools, creating breeding grounds. When floods recede, they leave behind a different landscape of permanent, vegetated water sources. The mosquitoes that thrive in these changing conditions are not all the same; some prefer the temporary puddles of the rainy season, while others cling to the steady, slow-moving streams left behind by floods. Understanding which species are present, where they live, and whether they carry the malaria parasite is the key to stopping the disease. If the mix of mosquitoes changes because of flooding or climate shifts, the strategies used to protect people must change with them.
A team of researchers recently set out to map this invisible landscape in the Kasese District, a region known for its history of severe flooding. Between February and May of 2025, they visited 154 households in villages situated near three major rivers. Their goal was to catch the mosquitoes that rest inside and outside these homes, identify exactly what kind they were, and check if any of them were infected with the malaria parasite. They used simple, battery-powered light traps placed near sleeping areas and in the trees outside, collecting the insects overnight. Once caught, the mosquitoes were carefully examined under microscopes to determine their species, and the heads and chests of the female mosquitoes were tested in a laboratory to see if they carried the infectious stage of the malaria parasite.
The study revealed a complex picture of mosquito life in these flood-prone communities. The researchers found that mosquitoes were present in nearly 90 percent of the homes they visited, but the specific type of mosquito that causes the most malaria, known as Anopheles gambiae, was not the only player. While this species made up the majority of the catch, the team also identified several other types, including Anopheles funestus. This finding is significant because different mosquitoes have different habits. The Anopheles funestus species, for instance, tends to breed in larger, more permanent water bodies that remain even after the floodwaters recede. This suggests that even when the heavy rains stop and the temporary pools dry up, the risk of malaria does not necessarily disappear, as these other species can sustain transmission.
Perhaps the most surprising discovery concerned the relationship between the mosquitoes and the bed nets families use for protection. The researchers expected to find fewer mosquitoes in homes with many bed nets. Instead, they found the opposite: households with a large number of old, worn-out nets were more likely to have mosquitoes inside than homes with fewer, newer nets. This does not mean the nets are useless; rather, it suggests that families who have been bitten or know the risk is high are the ones who have accumulated nets over time. However, as these nets age, the insecticide that kills the mosquitoes wears off, leaving the families vulnerable. The study also noted that the presence of mosquitoes was higher in homes without screened windows, highlighting how simple structural changes could help keep the insects out.
When the researchers tested the mosquitoes for the malaria parasite, they found that the infection rate was low but present. Out of the hundreds of female mosquitoes tested, only three were found to be carrying the parasite. Crucially, all three of these infected mosquitoes belonged to the Anopheles funestus species. None of the more common Anopheles gambiae mosquitoes tested positive. This points to a specific danger: even if the most common mosquito species is not currently infected, the less common ones can still carry the disease, especially in areas where floods have altered the environment. The study was conducted during an unusually dry period, which likely kept the overall number of mosquitoes lower than usual, yet the researchers still detected active transmission.
The work underscores that malaria control cannot rely on a single approach. Because the landscape changes with the floods, the mix of mosquito species changes with it. The presence of multiple species, including those that breed in permanent water and those that rest indoors, means that the disease can persist through different seasons and weather patterns. The researchers conclude that to protect communities in Kasese, health programs need to look beyond just the most common mosquito. They must account for the diverse habits of all the species present and ensure that protective measures, like bed nets, are replaced before they lose their power. By understanding the specific ways these insects adapt to a flood-prone world, communities can better prepare for the next season, regardless of whether the rains bring a deluge or a drought.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.