Entomological and Anthropological Factors Contributing to Persistent Malaria Transmission in Kenya, Ethiopia, and Cameroon

Abstract

Introduction: In order to improve our understanding of the fundamental limits of core interventions and guide efforts based on prioritization and identification of effective/novel interventions with great potentials to interrupt persistent malaria transmission in the context of high vector control coverage, the drivers of persistent disease transmission were investigated in three eco-epidemiological settings; forested areas in Cameroon, coastal area in Kenya and highland areas in Ethiopia.

Methods: Mosquitoes were sampled in three eco-epidemiological settings using different entomological sampling techniques and analysed for Plasmodium infection status and blood meal origin in blood-fed specimens. Human behavioural surveys were conducted to assess the knowledge and attitude of the population on malaria and preventive measures, their night activities, and sleeping pattern. The parasitological analysis was conducted to determine the prevalence of Plasmodium infection in the population using rapid diagnostic tests.

Results: Despite the diversity in the mosquito fauna, their biting behaviour was found to be closely associated to human behaviour in the three settings. People in Kenya and Ethiopia were found to be more exposed to mosquito bites during the early hours of the evening (18-21h) while it was in the early morning (4-6 am) in Cameroon. Malaria transmission was high in Cameroon compared to Kenya and Ethiopia with over 50% of the infected bites recorded outdoors. The non-users of LLINs were 2.5 to 3 times more likely to be exposed to the risk of acquiring malaria compared to LLINs users. Malaria prevalence was high (42%) in Cameroon, and more than half of the households visited had at least one individual infected with Plasmodium parasites.

Conclusions: The study suggests high outdoor malaria transmission occurring in the three sites with however different determinants driving residual malaria transmission in these areas.

Keywords: Cameroon; Ethiopia; Kenya; human behavior; malaria vectors; persistent malaria transmission.

Figure 1.

Map showing the study sites in the 3 sub-Saharan African malaria-endemic countries.

Figure 2.

Anopheline mosquito species composition and behavior from Kenya, Ethiopia, and Cameroon.

Figure 3.

Hourly biting activity of Anopheles mosquitoes both indoors (black lines) and outdoors (green lines) for the Anopheles vector and Anopheles gambiae sensu lato. Gray shading represents the proportion of children aged 6–14 years asleep at each hour of the night.

Figure 4.

Exposure risk to indoor and outdoor mosquito bites with age category in Ethiopia, Cameroon, and Kenya. A1, A2, and A3 represent directely measured human biting rate and human location for Anopheles gambiae sensu lato in Ethiopia, Cameroon, and Kenya, respectively. B1, B2, and B3 represent behavior-adjusted biting rate for an individual for An. gambiae and C1, C2, and C3 for Anopheles coustani, Anopheles moucheti, and Anopheles funestus, respectively, for Ethiopia, Cameroon, and Kenya.