Bionomics of Anopheline species and malaria transmission dynamics along an altitudinal transect in Western Cameroon

Abstract

BackgroundHighland areas of Africa are mostly malaria hypoendemic, due to climate which is not appropriate for anophelines development and their reproductive fitness. In view of designing a malaria control strategy in Western Cameroon highlands, baseline data on anopheline species bionomics were collected.MethodsLongitudinal entomological surveys were conducted in three localities at different altitudinal levels. Mosquitoes were captured when landing on human volunteers and by pyrethrum spray catches. Sampled Anopheles were tested for the presence of Plasmodium circumsporozoite proteins and their blood meal origin with ELISA. Entomological parameters of malaria epidemiology were assessed using Mac Donald's formula.ResultsAnopheline species diversity and density decreased globally from lowland to highland. The most aggressive species along the altitudinal transect was Anopheles gambiae s.s. of S molecular form, followed in the lowland and on the plateau by An. funestus, but uphill by An. hancocki. An. gambiae and An. ziemanni exhibited similar seasonal biting patterns at the different levels, whereas different features were observed for An. funestus. Only indoor resting species could be captured uphill; it is therefore likely that endophilic behaviour is necessary for anophelines to climb above a certain threshold. Of the ten species collected along the transect, only An. gambiae and An. funestus were responsible for malaria transmission, with entomological inoculation rates (EIR) of 90.5, 62.8 and zero infective bites/human/year in the lowland, on the plateau and uphill respectively. The duration of gonotrophic cycle was consistently one day shorter for An. gambiae as compared to An. funestus at equal altitude. Altitudinal climate variations had no effect on the survivorship and the subsequent life expectancy of the adult stage of these malaria vectors, but most probably on aquatic stages. On the contrary increasing altitude significantly extended the duration of gonotrophic cycle and reduced: the EIR, their preference to human blood and consequently the malaria stability index.ConclusionMalaria epidemiological rooting in the outskirts of Western Cameroon highlands evolves with increasing altitude, gradually from stable to unstable settings. This suggests a potential risk of malaria epidemic in highlands, and the need for a continuous epidemiological surveillance.

Plasmodium index, prevention, and control of malaria in Dschang municipality, Cameroon

“…[17,18] Many epidemiological studies are documented on malaria in several parts of Cameroon with regards to vectors/treatment dynamics. [19][20][21][22][23] The PI of 15.3% obtained in this study is much lower than the 37% reported by Couprie et al [24] in 1990 from Bamendjin, which is almost in the same latitude as Dschang. This could be explained by the fact that Dschang is relatively urban, while Bamendjin is a rural area.…”

Advances and Perspectives in the Study of the Malaria Mosquito Anopheles funestus

“…1A). Being predominantly a savannah mosquito [18], this malaria vector is present in many other areas, such as high altitude zones (900 m in Madagascar [19], 1400 m in Central Africa [20] and up to 2000 m in Kenya [21]) and forested areas of West and Central Africa [18,[22][23][24][25]. Moreover, it can inhabit extreme dry conditions in the Sahel, when suitable breeding place are available, such as human-made irrigation zones [26,27].…”

Distribution of Plasmodium falciparum gametocytes and malaria-attributable fraction of fever episodes along an altitudinal transect in Western Cameroon

“…Surprisingly, malaria prevalence at Djuttitsa was higher than expected from the entomological inoculation rate previously determined [40]. This discrepancy may be due to human migration.…”