Measuring changes in Plasmodium falciparum census population size in response to sequential malaria control interventions

Here we introduce a new endpoint “census population size” to evaluate the epidemiology and control of Plasmodium falciparum infections, where the parasite, rather than the infected human host, is the unit of measurement. To calculate census population size, we rely on a definition of parasite variation known as multiplicity of infection ([Formula: see text]), based on the hyper-diversity of the [Formula: see text] multigene family. We present a Bayesian approach to estimate [Formula: see text] from sequencing and counting the number of unique DBLα tags (or DBLα types) of [Formula: see text] genes, and derive from it census population size by summation of [Formula: see text] in the human population. We track changes in this parasite population size and structure through sequential malaria interventions by indoor residual spraying (IRS) and seasonal malaria chemoprevention (SMC) from 2012 to 2017 in an area of high-seasonal malaria transmission in northern Ghana. Following IRS, which reduced transmission intensity by > 90% and decreased parasite prevalence by ~40–50%, significant reductions in [Formula: see text] diversity, [Formula: see text] , and population size were observed in ~2,000 humans across all ages. These changes, consistent with the loss of diverse parasite genomes, were short lived and 32-months after IRS was discontinued and SMC was introduced, [Formula: see text] diversity and population size rebounded in all age groups except for the younger children (1–5 years) targeted by SMC. Despite major perturbations from IRS and SMC interventions, the parasite population remained very large and retained the [Formula: see text] population genetic characteristics of a high-transmission system (high [Formula: see text] diversity; low [Formula: see text] repertoire similarity) demonstrating the resilience of P. falciparum to short-term interventions in high-burden countries of sub-Saharan Africa.