High Vector Diversity and Malaria Transmission Dynamics in Five Sentinel Sites in Cameroon

Abstract

BackgroundMalaria remains one of the main causes of morbidity and mortality in Cameroon. To inform vector control intervention decision making, malaria vector surveillance was conducted monthly from October 2018 to September 2020 in five selected sentinel sites (Gounougou and Simatou in the North, Bonabéri, Mangoum and Nyabessang in the South).MethodsHuman landing catches (HLCs), U.S. Centers for Disease Control and Prevention (CDC) light traps, and pyrethrum spray catches (PSCs) were used to assess vector density and species composition, human biting rate (HBR), endophagic index, indoor resting density (IRD), parity, sporozoite infection rates, entomological inoculation rate (EIR), and Anopheles vectorial capacity. ResultsA total of 139,322 Anopheles mosquitoes from 21 species were collected across all sites and methods. Out of the 21 species, eleven were implicated in malaria transmission including An. gambiae s.l., An. funestus s.l., An. nili, An. moucheti, An. paludis, An. demeilloni, An. pharoensis, An. ziemanni, An. multicinctus, An. rufipes, and An. marshallii. Anopheles gambiae s.l. remains the major malaria vector (71% of the total Anopheles) collected across all sites, though An. moucheti and An. paludis had highest sporozoite rates in Nyabessang. The mean indoor HBR of Anopheles ranged from 11 bites/person/night (b/p/n) in Bonabéri to 104 b/p/n in Simatou, while outdoors, it varied from 24.2 b/p/n in Mangoum to 98.7 b/p/n in Simatou. Anopheles gambiae s.l. was actively biting until at least 8:00 a.m., and similarly for An. moucheti in Nyabessang. The mean Anopheles IRD was 17.1 females/room, and the parity rate was 68.9%. The monthly mean EIRs recorded was 46.1 infective bites/person/month (ib/p/m) in Gounougou, 91.2 ib/p/m in Simatou, 38.2 ib/p/m in Mangoum, 28.4 ib/p/m in Nyabessang, and 19.9 ib/p/m in Bonabéri. Anopheles gambiae s.l. was confirmed as the main malaria vector with the highest vectorial capacity in all sites based on sporozoite rate, except in Nyabessang. ConclusionThese findings highlight the high malaria transmission occurring in Cameroon and will support the National Malaria Control Program to design evidence-based malaria vector control strategies, effective and integrated vector control interventions deployment to reduce malaria transmission and burden in Cameroon, where several Anopheles species could potentially maintain year-round transmission.

Entomological longitudinal surveys in two contrasted eco-climatic settings in Cameroon reveal a high malaria transmission from Anopheles funestus associated with GSTe2 metabolic resistance

“…The presence of An. nili s.s as the sole species of the group is similar to the studies conducted in Nyabessang (Southern Region) [34], in the Northern part of the Benin [35], in the Southern and Western forest areas of Côte d'Ivoire [36] and in the Sudano-Guinean Zone of Senegal [37]. Secondary malaria vectors such as An.…”

“…nili s.l all had very high parity rates ranging from 52-100%, showing that vectors lived long enough to complete the sporogony cycle of the parasite to become infectious. Similar observations were highlighted by Fondjo et al [34] in different localities of the country. This could indicate a limited e cacy of vector control tools in these locations potentially associated with escalation of pyrethroid resistance [40].…”

Considerations for first field trials of low-threshold gene drive for malaria vector control

“…Measurement of both entomological and epidemiological efficacy is likely to be more complicated where the gene drive system is released in a single species but where there are multiple species of Anopheles malaria vectors at the release location. Therefore, any change in the EIR of target populations from release of the gene drive system could be partially confounded by continuing pathogen transmission by other sibling species, or by other malaria vector species, such as Anopheles funestus [36][37][38]. Modelling may help to predict the full impact if these other vector species are also targeted as there may be non-linear relationships between species abundance and malaria prevalence as transmission drops to low levels.…”