Mosquito vector composition and biting behavior of malaria vectors in forest versus humid savanna eco-epidemiological settings of Cameroon

BACKGROUND: The effectiveness of long-lasting insecticidal nets (LLIN) depends largely on the biting behaviour of the mosquito vectors. Therefore, understanding vector bionomics in a given epidemiological setting is essential for evaluating the impact of these malaria vector control tools. This study presents the entomological profile of malaria in two ecologically distinct settings in Cameroon, Mfou, a forest region, and Tibati, a savannah region. METHODS: Adult mosquitoes were collected both outdoors and indoors in randomly selected households between April and July 2019 using Human Landing Catches (HLCs). After morphological identification of the mosquitoes, a subset of anopheline mosquitoes from each species was dissected to determine parity status. DNA from the head and thorax was used for molecular analysis to identify individual mosquitoes to the An. gambiae complex and An. funestus group, and to detect Plasmodium infection. Entomological Inoculation Rate (EIR) was estimated based on Plasmodium infection rate as revealed by qPCR. RESULTS: A total of 3,651 Anopheles mosquitoes were collected (1,817 in Mfou and 1,834 in Tibati) and identified as belonging to 9 vector species: Anopheles gambiae sensu stricto (s.s.), An. coluzzii, An. funestus s.s., An. leesoni, An. moucheti, An. nili, An. ziemanni, An. paludis and An. pharoensis. The predominant vector was Anopheles gambiae s.l. in Mfou (68.96%; 1253/1817) with An. gambiae s.s. representing 79.22% of the An. gambiae complex. In Tibati, An. funestus s.l. was the major vector, accounting for 49.95% (916/1834) of the total Anopheles collection, and An. funestus s.s. was the main species within the An. funestus group (97.41%). Overall, host-seeking activity was not significantly different between indoor and outdoor collections at either site, with 48.71% of females caught indoors in Mfou and 46.89% in Tibati. In both sites, a peak of aggressiveness was observed outdoors between 4-5 h in the morning, with a rate of 2.68 bites per person per hour in Mfou and 2.31 in Tibati. The EIR was higher in Mfou, with an overall EIR of 1.47 infectious bites per person per night indoors and 1.00 ib/p/n outdoors, than in Tibati (indoors EIR = 0.25 ib/p/n and outdoors EIR = 0.23 ib/p/n). In Mfou, An. gambiae s.s. was the primary vector (indoors EIR = 0.84 ib/p/n and outdoors EIR = 0.60 ib/p/n), while in Tibati, An. coluzzii and An. funestus s.s. contributed equally to malaria transmission (An. coluzzii: indoors EIR = 0.11 ib/p/n and outdoors EIR = 0.05 ib/p/n; An. funestus s.s.: indoors EIR = 0.15 ib/p/n and outdoors EIR = 0.05 ib/p/n). CONCLUSION: Our study confirmed the key epidemiological role of An. gambiae s.s., An. coluzzii and An. funestus s.s. as major malaria vectors in Cameroon. Notably, we recorded substantial outdoor and early morning biting activity by Anopheles mosquitoes in the two surveyed localities. These findings underscore the limitations of bed nets as a standalone intervention and emphasize the need for complementary control strategies targeting both indoor and outdoor mosquito populations.