Fitness costs of pfhrp2 and pfhrp3 deletions underlying diagnostic evasion in malaria parasites

Abstract

BackgroundRapid diagnostic tests based on detection of histidine rich proteins (HRP) are widely used for malaria diagnosis, but parasites carrying pfhrp deletions can evade detection and are increasing in frequency in some countries. Models aim to predict conditions under which pfhrp2 and/or pfhrp3 deletions will increase, but a key parameter – the fitness cost of deletions – is unknownMethodsWe removed pfhrp2 and/or pfhrp3 from a Malawian parasite clone using CRISPR/Cas9 and measured fitness costs by conducting pairwise competition experiments.ResultsWe observed significant fitness costs of 0.087 ± 0.008 (1 s.e.) per asexual cycle for pfhrp2 deletion and 0.113 ± 0.008 (1 s.e.) for the pfhrp2/3 double deletion, relative to the unedited progenitor parasite. The results demonstrate ∼10% reduced survival of parasites bearing deletions of these loci.ConclusionsPrior modelling suggested that diagnostic selection may drive increased frequency of pfhrp2 and pfhrp3 deletions when fitness costs are ≤10%. Our laboratory competition experiments are consistent with costs of pfhrp2/3 deletions lying at this critical tipping point. These results may inform future modelling efforts and help us to understand why pfhrp2/3 deletions are increasing in some locations (Ethiopia/Eritrea) but not in others (Mekong region).