Bionomics and vectorial role of anophelines in wetlands along the volcanic chain of Cameroon

Abstract

Background: The epidemiological profiles of vector-borne diseases, such as malaria, are strongly associated with landscape components. The reduction of malaria burden in endemic and epidemic regions mainly depends on knowledge of the malaria-transmitting mosquito species, populations and behavioural characteristics, as well as malaria exposure risks. This work aimed at carrying out a holistic study in order to characterise Anopheles species in relation to human malaria in seven wetlands along the lower section of the volcanic chain of Cameroon.

Results: Eight malaria vectors: Anopheles arabiensis, An. coluzzii, An. funestus (s.s.), An. gambiae, An. hancocki, An. melas, An. nili and An. ziemanni, were found biting humans. Anopheles gambiae was widespread; however, it played a secondary role in the Ndop plain where An. ziemmani was the primary vector species (79.2%). Anophelines were more exophagic (73.6%) than endophagic (26.4%), showing a marked nocturnal activity (22:00-4:00 h) for An. coluzzii and An. gambiae while An. funestus (s.s.) was mostly caught between 1:00 and 6:00 h and An. ziemanni having an early evening biting behaviour (18:00-00:00 h). Female Anopheles were mostly observed to have relative high parity rates (≥ 70%), with the exception of the Meanja site where species parity varies from 46 to 55%. Overall, the transmission level was low with entomological inoculation rates estimated to 0.7 infected bites per person per month (ib/p/mth) in Tiko and Ndop, 1.4 ib/p/mth in Mamfe and 2.24 ib/p/mth in Santchou.

Conclusions: The present study represents detailed Anopheles vector characterisation from an understudied area along the volcanic chain of Cameroon with endemic malaria transmission. The significant differences in bionomics and Anopheles species distribution within the studied wetlands, highlights the importance of providing baseline data and an opportunity to assess the outcome of ongoing malaria control interventions in the country.

Keywords: Anopheles vectors; Malaria; Volcanic chain of Cameroon; Volcanic massif; Wetlands.

Fig. 1

3D map of the study area

Fig. 2

Main genera of mosquitoes identified morphologically from wetlands of the different massifs of the volcanic chain of Cameroon. A significant difference based on a Chi-square test (P < 0.0001) was noted in the mosquito distribution for all sites

Fig. 3

Diversity of Anopheles species (identified morphologically and using molecular techniques) from wetlands of major volcanic massifs across the study area. A significant difference based on a Chi-square test (P < 0.0001) was noted in anopheline abundance in all sites

Fig. 4

Indoor and outdoor exposure to major anophelines per wetland. Anophelines were mostly collected outdoors; note that there were no specimens collected indoors in Kumba and Mamfe. t-test statistical significance was determined using the Boferonni-Dunn method for each Anopheles species biting behaviour per wetland. ^#P = 0.0986, *P < 0.05, **P < 0.001. Abbreviation: ns, not significant

Fig. 5

Biting cycles of most predominant anophelines collected indoors (upper panels) and outdoors (lower panels) per wetland. An. coluzzii and An. gambiae were the most abundant specimens sampled both indoors and outdoors; An. ziemanni bites early in the evening