Intrinsic multiplication rate variation and plasticity of human blood stage malaria parasites

Abstract

Pathogen multiplication rate is theoretically an important determinant of virulence, although often poorly understood and difficult to measure accurately. We show intrinsic asexual blood stage multiplication rate variation of the major human malaria parasite Plasmodium falciparum to be associated with blood-stage infection intensity in patients. A panel of clinical isolates from a highly endemic West African population was analysed repeatedly during five months of continuous laboratory culture, showing a range of exponential multiplication rates at all timepoints tested, mean rates increasing over time. All isolates had different genome sequences, many containing within-isolate diversity that decreased over time in culture, but increases in multiplication rates were not primarily attributable to genomic selection. New mutants, including premature stop codons emerging in a few isolates, did not attain sufficiently high frequencies to substantially affect overall multiplication rates. Significantly, multiplication rate variation among the isolates at each of the assayed culture timepoints robustly correlated with parasite levels seen in patients at clinical presentation, indicating innate parasite control of multiplication rate that contributes to virulence.

DNA replication dynamics during erythrocytic schizogony in the malaria parasites Plasmodium falciparum and Plasmodium knowlesi

“…Both species were strikingly variable in the number of daughter cells produced per schizont. Such variation has been observed repeatedly in P. falciparum, with mean merozoite numbers of 15-22 reported in different strains [13,[21][22][23]. This cannot be entirely due to asynchrony in cultured cells: for example, the majority of P. knowlesi cells entered S-phase within a single hour, yet nuclear numbers were extremely variable at 31hpi, when just 2h later the great majority of these schizonts would burst.…”

How Many Is Enough? - Challenges of Multinucleated Cell Division in Malaria Parasites

“…Finally, all these parameters should be linked to parasite multiplication rates to predict how they might correlate with disease severity. Knowing that multiplication rates can increase throughout culture adaptation, we further need to assess the validity of those cellular parameters in samples that have more recently been isolated from patients (Stewart et al, 2020). Ultimately, we advocate for the systematic assessment of merozoite number in Plasmodium mutants that develop a growth phenotype, so that we can expand our list of candidate proteins implicated in defining progeny numbers and advance our understanding of malaria parasites proliferation mechanisms.…”

“…In 3D7 average numbers of 22 have been reported (Dorin-Semblat et al, 2008;Garg et al, 2015). In newly isolated Ghanaian parasite strains, values between 16-24 were found, although those were only measured after six months of continuous in vitro culture and once multiplication rates had significantly increased (Stewart et al, 2020). The counted number of merozoites can, however, vary significantly depending on the used visualization method (Garg et al, 2015).…”

A heat-shock response regulated by the PfAP2-HS transcription factor protects human malaria parasites from febrile temperatures

“…Genome-wide sequence analysis has previously found that nonsense mutations arise in pfap2-hs during adaptation to culture conditions 30 , 31 , but are virtually absent from clinical isolates (in the www.malariagen.net/data/pf3k-5 dataset 32 , only one out of >2,500 isolates carries a high-confidence SNP resulting in a premature stop codon). The lack of mutations observed in clinical isolates suggests that there is a selection against loss-of-function mutations in PfAP2-HS during human infections, where parasites are frequently exposed to febrile conditions.…”