Diversity of anopheline species and malaria transmission dynamics in high-altitude areas of western Cameroon.

Background: Assessing vector bionomics and their role in transmission is crucial to improving vector control strategies. Several entomological studies have been conducted to describe malaria transmission in different eco-epidemiological settings in Cameroon; however, data gaps persist, particularly in the highland areas. This study aimed to characterize malaria vectors in three localities along an altitudinal gradient in the western region: Santchou (700 m), Dschang (1400 m) and Penka Michel (1500 m).

Methods: Human landing catches were conducted from May to June 2023 in 17 villages (including 10 health zones in Dschang, 4 in Santchou and 3 in Penka Michel) from 6:00 p.m. to 9:00 a.m. Mosquitoes were sorted into genera and all Anopheles species were identified using morphological taxonomic keys and species-specific Polymerase Chain reaction (PCR). Entomological indicators, including species composition, abundance, biting behaviour, infection rate and entomological inoculation rate (EIR) were assessed. Genomic DNA from the head and thorax was extracted and tested for Plasmodium infection by real-time PCR.

Results: A total of 2835 Anopheles mosquitoes were identified, including Anopheles gambiae sensu lato (s.l.) (82.88%), Anopheles funestus s.l. (15.92%), Anopheles nili (0.09%) and Anopheles ziemanni (1.11%), with An. gambiae s.l. being the most prevalent at all sites. Anopheles gambiae s.l. had a significantly higher human-biting rate at Penka Michel (45.25 bites/human/night) compared to Santchou (3.1 bites/human/night [b/h/n]) and Dschang (0.41 bites/human/night) (p-value < 0.001). It was also the main malaria vector, with an entomological inoculation rate (EIR) 13 times higher in Penka Michel than Santchou (1.11 vs. 0.08 infective bites/human/night). The data suggest a very focal distribution of infective An. gambiae s.l. mosquitoes. Plasmodium falciparum was the dominant malaria parasite (67% in Santchou, 62% in Penka Michel), but Plasmodium malariae (33% in Santchou, 31% in Penka Michel) and Plasmodium ovale (1.21% only in Penka Michel) infections were also detected.

Conclusion: The study highlights a difference in mosquito composition and host-seeking behaviour across altitudes, emphasizing the need for continued surveillance to monitor vector populations. To combat the persistence of malaria in Cameroon, it is crucial to implement additional tools like larviciding, integrated and environmental management, particularly against outdoor-biting mosquitoes, to prevent potential malaria outbreaks in these highland areas.