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


METHODS
Longitudinal 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.


RESULTS
Anopheline 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.


CONCLUSIONS
Malaria 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.
Tchuinkam
Timoléon
T
Laboratory of Applied Biology and Ecology, Department of Animal Biology, Faculty of Sciences, University of Dschang, PO Box 067 Dschang, Cameroon. timtchuinkam@yahoo.fr
Simard
Frédéric
F
Lélé-Defo
Espérance
E
Téné-Fossog
Billy
B
Tateng-Ngouateu
Aimé
A
Antonio-Nkondjio
Christophe
C
Mpoame
Mbida
M
Toto
Jean-Claude
JC
Njiné
Thomas
T
Fontenille
Didier
D
Awono-Ambéné
Herman-Parfait
HP
D000818:Animals; D000852:Anopheles / Q000254:growth & development* / Q000469:parasitology*; D001769:Blood / Q000276:immunology; D002163:Cameroon; D004463:Ecology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008288:Malaria / Q000635:transmission*; D010961:Plasmodium / Q000302:isolation & purification*; D015800:Protozoan Proteins / Q000302:isolation & purification; D018570:Risk Assessment
D015800:Protozoan Proteins; C041595:circumsporozoite protein, Protozoan