Defining malaria transmission dynamics in the Gambia

Though still affecting an important proportion of the world population, malaria has declined substantially in the last few years, thanks also to the scale up of interventions such as bed nets treated with insecticide. Such decrease has been observed also in sub-Saharan African countries. It is now recognised that the knowledge needed to support any elimination effort is limited and that a new attempt in this direction should be supported by a strong research component. This research program aims at understanding the dynamics of malaria transmission and the reasons why this can substantially differ within few kilometres. The populations of 12 villages will be intensively followed up for 3 transmission seasons to understand who the malaria carriers are and how the infection spreads across the populations. Information on the vector population, including the presence of insecticide resistance, and on the human behaviour will be collected to partly explain the likely differences between the study villages. The results of this research program will be important for any sub-Saharan African country willing to go towards elimination of malaria. They will be disseminated through international and regional conferences, and by international peer-reviewed publications and communications.

Malaria elimination came recently back onto the global public health agenda when a substantial malaria decrease was observed worldwide, including in sub-Saharan Africa. In The Gambia, malaria has markedly decreased over the last few years, a result attributed to the interventions' scale-up. Transmission will further decrease but the impact will not be uniform and pockets of transmission will remain. The objectives of this proposed research program is to understand the dynamics of malaria transmission in a context of high coverage of standard control interventions.
Six areas with substantial transmission have been identified and 2 villages per area (lowest and highest malaria prevalence), selected and intensively followed up (monthly bleeds and passive case detection) for 3 transmission seasons. Blood samples will be screened for infection and then those positive genotyped. The human reservoir will be defined by membrane feeding assays and by detecting gametocytes with molecular methods. For the vector, target-site, metabolic and behavioural resistance will be determined. For human behavioural factors, a mixed methods study design (qualitative and quantitative) will be used. Modelling will synthesize information, quantify uncertainty and generate new hypotheses.
The results of this research program will be important for any sub-Saharan African country willing to go towards elimination of malaria. They will be disseminated through conferences, and by international publications and communications.

The proposed research program has the potential of having a large impact on the way malaria control and elimination are tackled in sub-Saharan Africa. The component on the dynamics of transmission will provide knowledge on the residual foci of malaria infection in a context of high coverage of control interventions. It will identify some or most of the determinants (related to the vector and to human behaviour) maintaining these foci. In addition, it will provide information on whether it is possible and how to identify asymptomatic carriers and individuals infectious to mosquitoes. Therefore, the primary beneficiary from the research will be the Gambian National Malaria Control Program (NMCP) and the Gambians still living in areas with ongoing transmission. Results of this program will help the NMCP to better target residual foci of transmission and to decrease the risk of malaria transmission for the local populations. Considering that the situation in The Gambia is similar to other countries in the West African region, the corresponding NMCP will also be able to use the information produced to better target their efforts. This research program will also provide valuable information to international agencies, e.g. World Health Organization, involved in the formulation of guidelines related to malaria elimination or in the funding of elimination efforts.

The component on tools will result in a simple, easy-to-use, molecular diagnostic test to identify asymptomatic parasite carriers. The NMCPs (in African and in other endemic continents) and any other organization involved in malaria control/elimination activities will benefit enormously from the availability of such test(s) as they will be able to identify and immediately treat asymptomatic carriers. This should reduce the human reservoir and reduce or eliminate transmission. Though asymptomatic carriers are not ill, the availability of the test will allow better targeting them in campaigns aiming at treating all infected individuals. By decreasing the risk of unnecessarily treating uninfected people, it will reduce the occurrence of adverse drug reactions. Commercial private sector could use the results for the mass production of the test. Similarly, the proteomics study will generate knowledge that could be used by the commercial private sector to develop a new diagnostic test.