Complex non-falciparum transmission and widespread insecticide resistance sustain hyperendemic malaria in Penka-Michel, a focus of the Cameroon highlands

A 12-month longitudinal entomological study (September 2023-August 2024) in the Western Highlands of Cameroon (Penka-Michel) investigated malaria transmission dynamics and insecticide resistance markers, including target-site resistance (L1014F, N1575Y, G119S- Ace1 ) and metabolic resistance (E205D -CYP6P3 , L119F -GSTe2 , CYP6P9a/b ) mutations. Malaria transmission was driven by the coexistence of three species: Anopheles funestus (43.7%), Anopheles gambiae (42.9%), and Anopheles ziemanni (13.5%). The study site was hyperendemic with an annual Entomological Inoculation Rate (EIR) of 839.5 infective-bites/human/year. Plasmodium falciparum predominated at 51.9% (68/131), though a significant non- falciparum burden was observed ( P. malariae : 14.5%, 19/131; P. ovale : 15.3%, 20/131), including mixed infections (18.3%, 24/131). Anopheles funestus was the principal driver (Infection Rate, IR, of 7.8%) for P. falciparum and P. ovale curtisi, which peaked in the later rainy season (November). Anopheles gambiae (IR=5.4%) primarily vectored P. malariae , maintaining a sustained peak during the dry season (January). Widespread insecticide resistance was marked by high frequencies of target-site and metabolic resistance markers. Possible associations were observed between L119F-GSTe2 mutations with P. ovale curtisi transmission (IRR=1.15, p =0.03), and L1014F-kdr mutation with P. malariae (IRR=2.2, p =0.04). These dynamics underscore the intricate nature of a multifaceted, species-diverse system, where seasonal vector efficiency and insecticide resistance perpetuate the hyperendemicity of the frequently disregarded non- falciparum malaria species.