The burden of malaria remains high in many regions of Africa, despite widespread availability of malaria control measures. The recent report of increases in malaria infection rates in Africa highlights the need to ensure that current and future interventions target the key sources of malaria transmission in these settings. The susceptibility of an Anopheles mosquito to permit ingested Plasmodium gametocytes to develop fully to the transmissible sporozoite stage, or vector competence, remains poorly understood. In Malawi and many other regions in southern and eastern Africa, Anopheles funestus and Anopheles arabiensis are now the most common malaria vectors and may have important variability in vector competence that has not been considered in control and elimination efforts. Our long-term goal is to better understand the contributions of both humans and vectors to transmission of malaria parasites to design effective vector control strategies for the highest-burden regions of Africa. We have the unique opportunity to conduct a rigorous assessment of the vector competence of the key malaria vectors in Malawi through our on-going projects in the Malawi International Center of Excellence in Malaria Research (ICEMR). The proposed study is being led by an epidemiologist who serves as the project leader for a transmission study within the ICEMR that focuses on the human to vector phases of the cycle, and an entomologist who leads the ICEMR entomology core. We have established a well-functioning insectary and routinely collect live female Anopheles mosquitoes from several high transmission settings in the region. In addition, we are establishing a cohort of children and adults who will be followed to identify P. falciparum infections that contain gametocytes. We will use specimens collected from these gametocyte-infected donors to compare vector competence between colony-reared An. gambiae Kisumu and field-caught An. funestus and An. arabiensis to test the hypotheses that vector competence of natural An. funestus and An. arabiensis differs from each other and from the colony strain. We will further evaluate variation in vector competence among isofemale lines of the same Anopheles species to assess the heritability of vector competence. Finally, we propose comparing vector competence within the same species but from geographically isolated areas of Malawi. The expected outcomes of this proposal include estimates of vector competence for An. arabiensis and An. funestus. Identifying significant differences in vector competence among species, within species or based on region of origin, may indicate the need to investigate a genomic basis for vector competence. Our results will also impact the rational implementation of vector control measures in Malawi and other high transmission settings.
Anopheles funestus and Anopheles arabiensis are currently the main vectors of malaria parasites in many regions of Africa, yet critical aspects of their biology remain poorly characterized. Determining the natural variation of these vectors in modulating Plasmodium falciparum development may explain variation in the effectiveness of current and future malaria interventions. Characterizing variation within Anopheles species would also support future studies to understand the genetic basis of susceptibility to P. falciparum in these mosquito species and aid in planning future region-specific interventions.
