The Impact of Novel Vector Control Tools on Asymptomatic Plasmodium falciparum Infection Prevalence
and Transmission Potential
Project Summary
Malaria is a major cause of morbidity and mortality in many countries in the tropics and subtropics. Most malaria
programs focus on diagnosis and treatment of clinical infections and blanket vector control through bed net
distributions. This strategy does not adequately target the asymptomatic reservoir, which is the source of up to
95% of malaria transmission. There is a lack of understanding of the ability of many current and new malaria
control tools to shrink the asymptomatic reservoir because many studies evaluating interventions focus on
clinical incidence as the main outcome. Spatial repellents are a novel tool for malaria control. They release
volatile compounds that drive away mosquitos from houses. Spatial repellents might reduce clinical incidence
by up to 50%. Their impact on the prevalence of asymptomatic infections has not been systematically studied.
The ability of spatial repellents to reduce clinical incidence is currently being field-tested in a funded large-scale
cluster randomized trial in western Kenya. Our preliminary data shows that nearly half of all individuals in the
study site carried asymptomatic malaria infections at baseline. Given the importance of these infections as a
source of transmission, there is a need to understand whether spatial repellents can also reduce this reservoir
in order to assess their full potential to combat malaria. Here, we propose to study the impact of spatial repellents
on asymptomatic P. falciparum prevalence. The objectives of this application are to: 1) Quantify reductions
in asymptomatic prevalence after the introduction of spatial repellents. We will screen 9000 blood samples
currently being collected for P. falciparum infections by qPCR and microscopy. 2) Compare mosquito-to-
human and human-to-mosquito transmission in intervention and control clusters. We will quantify
gametocytes and compare parasite and gametocyte prevalence and density to vector density, sporozoite rate,
and entomological inoculation rate (EIR) at different time points before and after blood sample collections. The
outcomes of the proposed research include: 1) Knowledge of the potential of spatial repellents to reduce
asymptomatic prevalence, and 2) an understanding of the changes in mosquito-to-human and human-
to-mosquito transmission after introduction of spatial repellents. Our data on the relationships between
parasitological and entomological measures of transmission intensity, collected in 20 clusters at three timepoints,
will enable a better understanding on the impact of malaria control beyond the use of spatial repellents. Our work
aims to accelerate malaria elimination, and thus to improve the lives of people living in malaria-endemic
countries.
