Daily Survival and Human Blood Index of Major Malaria Vectors Associated with Oil Palm Cultivation in Cameroon and Their Role in Malaria Transmission

Objective: To describe the daily survival rate, biting habits, feeding behaviour, sporozoite and entomological inoculation rates of Anopheles species and their relative contribution to Plasmodium falciparum transmission in large-scale oil palm-growing zones in Cameroon.

Methods: Entomological surveys by employing human-landing catches, both indoors and outdoors, two nights per month for 12 months from October 2004.

Results: A total of 2485 Anopheles were collected and four species recorded: An. funestus, An. hancocki, An. gambiae s.s. and An. nili. There was substantial indoors to outdoors variation and seasonality in the distribution of the Anopheles population. All four species showed similar nocturnal biting patterns and were sympatrically involved in malaria transmission simultaneously or replacing each other seasonally. Their constant presence throughout the year and longevity suggest that transmission can occur at any time if parasite reservoirs are present in the area. The circumsporozoite protein rates were 5.8%, 6.3%, 8.4% and 4.1%; mean anthropophilic rates were 97.1%, 94.5%, 73.9% and 77.6%, respectively, for An. funestus, An. gambiae s.l, An. nili and An. hancocki. The annual entomological inoculation rate was 1077 infectious bites per person. Of those An. gambiae specimens testing positive for P. falciparum sporozoites, 69.01% were M form and 30.99% were S form.

Conclusion: Any vector control strategy intending to significantly reduce the malaria burden in the palm estate will have to take into account entomological heterogeneity in addition to ecological and socio-economic multiplicity.