Bionomics and distribution of malaria vectors in Kisumu city, Western Kenya: Implications for urban malaria transmission.

BACKGROUND

Increasing urbanization in tropical Africa may create new niches for malaria vectors, potentially leading to higher disease transmission rates. Vector control efforts remain largely targeted at ecologically rural bio-complexities with multiple hosts. Understanding mosquito species composition, ecology, host diversity and biting behavior in urban areas is crucial for planning effective control. This study assessed mosquito species diversity, abundance, behavioral patterns, and sporozoite infection rates of vectors along an urban-rural transect in Kisumu city, western Kenya.

METHODS

Indoor and outdoor host-seeking and resting adult mosquitoes were collected using Centers for Disease Control and Prevention miniature light traps (CDC-LT) and mechanical aspirators (Prokopack) along an urban-rural transect. Females mosquitoes collected were identified using morphological taxonomic keys to species level. Specimens belonging to the complex and group were further processed using polymerase chain reaction (PCR) to identify members of each complex/group. Subsequently, sporozoite infection rates of the anopheline mosquitoes were determined using a multiplexed real-time quantitative PCR (qPCR) assay.

RESULT

A total of 3,394 female mosquitoes were collected and identified. These comprised of s.l. (68%), group (19.8%), (7.8%), (2.6%), (1.6%), and (0.2%). All six species were found in urban zone, but only three were found in peri-urban and rural sites. Overall, urban collections accounted for the majority of these collections (55.5%) of mosquitoes collected, followed by those from peri-urban (30%) and rural sites (14.5%). Species distribution across the three ecotypes showed was the dominant species in urban (84.3%) and peri-urban (89%) sites, while s.s. was predominantly found in the rural zone (60.2%) alongside (39.7%). was the predominant species in peri-urban (98.4%) and rural (85.7%) areas, with accounted for 1.6% and 14.3%, respectively. In urban areas, all samples from the group were identified as s.s.. Majority (55.5%) of mosquitoes were collected indoors, while secondary vectors were primarily caught outdoors. Overall, sporozoite rates were higher outdoors 3.5% compared to indoors 1.45% in rural areas. Specifically, sporozoite infectivity rates for s.s and collected indoors in the rural zone was 2.5%, 1.4% and 1% respectively. Outdoors in rural areas, had a sporozoite rate of 5.3%, while had a rate of 2.1%. In peri-urban areas had a sporozoite rate of 2.3%. No sporozoites were detected in samples from urban sites.

CONCLUSION

The study highlights a shift of diversity of species towards urban areas with increased outdoor activity, and significant outdoor malaria transmission in rural and peri-urban areas, emphasizing the need for tools targeting outdoor-biting mosquitoes. The presence of in urban settings is of interest and highlights the critical importance of sustained entomological surveillance to inform integrated vector control and prevent future transmission risks.