Estimating merozoite release number and reinvasion efficiency in Plasmodium falciparum cell culture

Abstract

During its asexual growth, Plasmodium falciparum undergoes a number of 48 h intra-erythrocytic cycles, punctuated by reinvasion events. The biomass formation dynamics can be described by three key parameters: the period of the growth cycle (for P. falciparum, typically 48 h), the merozoite release number (variable between 8 and 32), and the reinvasion efficiency (variable between 20 and 40% in cell cultures). An accurate estimation of these parameters is important to describe growth dynamics, and for evaluating working mechanisms of anti-malaria drugs. Standard techniques for the estimation of merozoite release number and reinvasion efficiency are based on interpretation of microscope images, typically involve fairly low numbers of observations and are laborious. Here, we employ a combined experimental and mathematical modelling approach that is based on metabolic end-product formation and parasitaemia dynamics, to quantify the key parameters for Plasmodium biomass formation in cell cultures in vitro. We present experimental data for Plasmodium falciparum, together with a mechanistic model for the mathematical analysis, and finally an easy-to-use method for a direct analysis of the experimental data. The results are in agreement with previously published results, but – importantly – are average values for all cells in the culture, i.e. based on a large number of cells, and are reproducible between independent experiments.