Complexity of the Malaria Vectorial System in Cameroon: Contribution of Secondary Vectors to Malaria Transmission

BackgroundAs part of a study to determine the impact of insecticide resistance on the effectiveness of long-lasting insecticide treated nets (LLINs) in the north of Cameroon, the unexpectedly high density and anthropophilic behaviour of Anopheles rufipes lead us to investigate this species bionomics and role in human malaria parasite transmission.MethodsFor four consecutive years (2011–2014), annual cross-sectional sampling of adult mosquitoes was conducted during the peak malaria season (September-October) in three health districts in northern Cameroon. Mosquitoes sampled by human landing catch and pyrethrum spray catch methods were morphologically identified, their ovaries dissected for parity determination and Anopheles gambiae siblings were identified by molecular assay. Infection with P. falciparum and blood meal source in residual fauna of indoor resting anopheline mosquitoes were determined by enzyme-linked-immunosorbent assays.Results Anopheles gambiae (sensu lato) (s.l.) comprised 18.4% of mosquitoes collected with An. arabiensis representing 66.27% of the sibling species. The proportion of An. rufipes (2.7%) collected was high with a human-biting rate ranging between 0.441 and 11.083 bites/person/night (b/p/n) and an anthropophagic rate of 15.36%. Although overall the members of An. gambiae complex were responsible for most of the transmission with entomological inoculation rates (EIR) reaching 1.221 infective bites/person/night (ib/p/n), An. arabiensis and An. coluzzii were the most implicated. The roles of An. funestus, An. pharoensis and An. paludis were minor. Plasmodium falciparum circumsporozoite protein rate in Anopheles rufipes varied from 0.6 to 5.7% with EIR values between 0.010 and 0.481 ib/p/n.ConclusionsThe study highlights the epidemiological role of An. rufipes alongside the members of the An. gambiae complex, and several other sympatric species in human malaria transmission during the wet season in northern Cameroon. For the first time in Cameroon, An. rufipes has been shown to be an important local malaria vector, emphasising the need to review the malaria entomological profile across the country as pre-requisite to effective vector management strategies.

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“…nili and An. moucheti ) have been described [10] with nine secondary vectors of local importance ( An. paludis , An.…”

Section: Discussionmentioning

confidence: 99%

“…nili (Theobald, 1904) and An. moucheti Evans, 1925 are classified as major vectors [10]. The other species amongst which are An.…”

Section: Introductionmentioning

confidence: 99%

Role of Anopheles (Cellia) rufipes (Gough, 1910) and other local anophelines in human malaria transmission in the northern savannah of Cameroon: a cross-sectional survey

et al. 2017

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“…[8]. However, as studies of malaria transmission have identified the presence of more than one significant malaria vector within some regions [37], [38] there is again reason to doubt the validity of this assumption in many contexts.…”

Section: Methodsmentioning

confidence: 99%

Malaria in Africa: Vector Species' Niche Models and Relative Risk Maps

2007

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A central theoretical goal of epidemiology is the construction of spatial models of disease prevalence and risk, including maps for the potential spread of infectious disease. We provide three continent-wide maps representing the relative risk of malaria in Africa based on ecological niche models of vector species and risk analysis at a spatial resolution of 1 arc-minute (9 185 275 cells of approximately 4 sq km). Using a maximum entropy method we construct niche models for 10 malaria vector species based on species occurrence records since 1980, 19 climatic variables, altitude, and land cover data (in 14 classes). For seven vectors (Anopheles coustani, A. funestus, A. melas, A. merus, A. moucheti, A. nili, and A. paludis) these are the first published niche models. We predict that Central Africa has poor habitat for both A. arabiensis and A. gambiae, and that A. quadriannulatus and A. arabiensis have restricted habitats in Southern Africa as claimed by field experts in criticism of previous models. The results of the niche models are incorporated into three relative risk models which assume different ecological interactions between vector species. The “additive” model assumes no interaction; the “minimax” model assumes maximum relative risk due to any vector in a cell; and the “competitive exclusion” model assumes the relative risk that arises from the most suitable vector for a cell. All models include variable anthrophilicity of vectors and spatial variation in human population density. Relative risk maps are produced from these models. All models predict that human population density is the critical factor determining malaria risk. Our method of constructing relative risk maps is equally general. We discuss the limits of the relative risk maps reported here, and the additional data that are required for their improvement. The protocol developed here can be used for any other vector-borne disease.

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“…Rota is in a rural setting, on the marshes of Lake Victoria in Western Kenya, with a tropical climate and annual rainfall Ͼ1,000 mm. In all three highly endemic malaria localities, transmission is perennial, with inoculation rates of Ϸ200 (Tibati), Ϸ300 (Simbock), and 100-300 (Rota) infective bites per human per year (2,3,37). keys (6, 7), the mosquitoes were dissected in a saline solution on the morning of their collection in Cameroon and 1 week after collection in Rota to allow for the development of oocysts in infected females.…”

Section: Methodsmentioning

confidence: 99%

“…Prevention and cure of the disease are major publichealth challenges that are tackled by using several strategies, among them vector control. The transmission of Plasmodium falciparum, the agent of malignant malaria, involves a complex vectorial system consisting of Ϸ10 Anopheles species, colonizing different ecoclimatic settings, regions, and seasons in strongly variable relative abundances (2)(3)(4)(5).…”

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Population genetic structure of Plasmodium falciparum in the two main African vectors, Anopheles gambiae and Anopheles funestus

Annan

Durand

Ayala

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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We investigated patterns of genetic diversity of Plasmodium falciparum associated with its two main African vectors: Anopheles gambiae and Anopheles funestus. We dissected 10,296 wildcaught mosquitoes from three tropical sites, two in Cameroon (Simbock and Tibati, separated by 320 km) and one in Kenya (Rota, >2,000 km from the other two sites). We assayed seven microsatellite loci in 746 oocysts from 183 infected mosquito guts. Genetic polymorphism was very high in parasites isolated from both vector species. The expected heterozygosity (HE) was 0.79 in both species; the observed heterozygosities (HO) were 0.32 in A. funestus and 0.42 in A. gambiae, indicating considerable inbreeding within both vector species. Mean selfing (s) between genetically identical gametes was s ‫؍‬ 0.33. Differences in the rate of inbreeding were statistically insignificant among sites and between the two vector species. As expected, because of the high rate of inbreeding, linkage disequilibrium was very high; it was significant for all 21 loci pairs in A. gambiae and for 15 of 21 pairs in A. funestus, although only two pairwise comparisons were between loci on the same chromosome. Overall, the genetic population structure of P. falciparum, as evaluated by F statistics, was predominantly clonal rather than panmictic, a population structure that facilitates the spread of antimalarial drug and vaccine resistance and thus may impair the effectiveness of malaria control efforts. malaria ͉ epidemiology ͉ evolutionary genetics ͉ Cameroon ͉ Kenya M alaria is the most significant and widespread vectortransmitted human disease, accounting yearly for several hundred million clinical cases and Ͼ2 million deaths, mostly affecting young children and pregnant women in subSaharan Africa (1). Prevention and cure of the disease are major publichealth challenges that are tackled by using several strategies, among them vector control. The transmission of Plasmodium falciparum, the agent of malignant malaria, involves a complex vectorial system consisting of Ϸ10 Anopheles species, colonizing different ecoclimatic settings, regions, and seasons in strongly variable relative abundances (2-5).The two most important vectors of malignant malaria in Africa are Anopheles gambiae and Anopheles funestus because of their widespread distribution, highly anthropophilic and endophilic behavior, and long life spans (6, 7). A. gambiae is the most important vector throughout Africa and the most extensively studied Anopheles species (8). The effectiveness of malaria transmission emerges from the complementary ecoclimatic attributes and seasonal patterns of both species. A. funestus breeds in permanent larval sites that enable this species, in regions of seasonal transmission, to extend parasite transmission far into the dry season, after the temporary breeding pools of A. gambiae have dried out (7, 9-11).Differences in the biology and ecology of these two main vectors might entail a differential impact on the genetic composition of the P. falciparum populations they harbo...

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Complexity of the Malaria Vectorial System in Cameroon: Contribution of Secondary Vectors to Malaria Transmission

Cited by 129 publications

References 32 publications

Role of Anopheles (Cellia) rufipes (Gough, 1910) and other local anophelines in human malaria transmission in the northern savannah of Cameroon: a cross-sectional survey

Role of Anopheles (Cellia) rufipes (Gough, 1910) and other local anophelines in human malaria transmission in the northern savannah of Cameroon: a cross-sectional survey

Malaria in Africa: Vector Species' Niche Models and Relative Risk Maps

Population genetic structure of Plasmodium falciparum in the two main African vectors, Anopheles gambiae and Anopheles funestus

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