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Fulltext A reference genome and methylome for the Plasmodium knowlesi A1-H.1 line

Benavente ED, de Sessions PF, Moon RW, Grainger M, Holder AA, Blackman MJ, et al.

Int J Parasitol, 2018 03;48(3-4):191-196.
PMID: 29258833 DOI: 10.1016/j.ijpara.2017.09.008

Plasmodium knowlesi, a common parasite of macaques, is recognised as a significant cause of human malaria in Malaysia. The P. knowlesi A1H1 line has been adapted to continuous culture in human erythrocytes, successfully providing an in vitro model to study the parasite. We have assembled a reference genome for the PkA1-H.1 line using PacBio long read combined with Illumina short read sequence data. Compared with the H-strain reference, the new reference has improved genome coverage and a novel description of methylation sites. The PkA1-H.1 reference will enhance the capabilities of the in vitro model to improve the understanding of P. knowlesi infection in humans.
Fulltext Identification and validation of a novel panel of Plasmodium knowlesi biomarkers of serological exposure

Herman LS, Fornace K, Phelan J, Grigg MJ, Anstey NM, William T, et al.

PLoS Negl Trop Dis, 2018 Jun;12(6):e0006457.
PMID: 29902183 DOI: 10.1371/journal.pntd.0006457

BACKGROUND: Plasmodium knowlesi is the most common cause of malaria in Malaysian Borneo, with reporting limited to clinical cases presenting to health facilities and scarce data on the true extent of transmission. Serological estimations of transmission have been used with other malaria species to garner information about epidemiological patterns. However, there are a distinct lack of suitable serosurveillance tools for this neglected disease.
METHODOLOGY/PRINCIPAL FINDINGS: Using in silico tools, we designed and expressed four novel P. knowlesi protein products to address the distinct lack of suitable serosurveillance tools: PkSERA3 antigens 1 and 2, PkSSP2/TRAP and PkTSERA2 antigen 1. Antibody prevalence to these antigens was determined by ELISA for three time-points post-treatment from a hospital-based clinical treatment trial in Sabah, East Malaysia (n = 97 individuals; 241 total samples for all time points). Higher responses were observed for the PkSERA3 antigen 2 (67%, 65/97) across all time-points (day 0: 36.9% 34/92; day 7: 63.8% 46/72; day 28: 58.4% 45/77) with significant differences between the clinical cases and controls (n = 55, mean plus 3 SD) (day 0 p<0.0001; day 7 p<0.0001; day 28 p<0.0001). Using boosted regression trees, we developed models to classify P. knowlesi exposure (cross-validated AUC 88.9%; IQR 86.1-91.3%) and identified the most predictive antibody responses.
CONCLUSIONS/SIGNIFICANCE: The PkSERA3 antigen 2 had the highest relative variable importance in all models. Further validation of these antigens is underway to determine the specificity of these tools in the context of multi-species infections at the population level.
Fulltext Analysis of nuclear and organellar genomes of Plasmodium knowlesi in humans reveals ancient population structure and recent recombination among host-specific subpopulations

Diez Benavente E, Florez de Sessions P, Moon RW, Holder AA, Blackman MJ, Roper C, et al.

PLoS Genet, 2017 Sep;13(9):e1007008.
PMID: 28922357 DOI: 10.1371/journal.pgen.1007008

The macaque parasite Plasmodium knowlesi is a significant concern in Malaysia where cases of human infection are increasing. Parasites infecting humans originate from genetically distinct subpopulations associated with the long-tailed (Macaca fascicularis (Mf)) or pig-tailed macaques (Macaca nemestrina (Mn)). We used a new high-quality reference genome to re-evaluate previously described subpopulations among human and macaque isolates from Malaysian-Borneo and Peninsular-Malaysia. Nuclear genomes were dimorphic, as expected, but new evidence of chromosomal-segment exchanges between subpopulations was found. A large segment on chromosome 8 originating from the Mn subpopulation and containing genes encoding proteins expressed in mosquito-borne parasite stages, was found in Mf genotypes. By contrast, non-recombining organelle genomes partitioned into 3 deeply branched lineages, unlinked with nuclear genomic dimorphism. Subpopulations which diverged in isolation have re-connected, possibly due to deforestation and disruption of wild macaque habitats. The resulting genomic mosaics reveal traits selected by host-vector-parasite interactions in a setting of ecological transition.
Fulltext Normocyte-binding protein required for human erythrocyte invasion by the zoonotic malaria parasite Plasmodium knowlesi

Moon RW, Sharaf H, Hastings CH, Ho YS, Nair MB, Rchiad Z, et al.

Proc Natl Acad Sci U S A, 2016 Jun 28;113(26):7231-6.
PMID: 27303038 DOI: 10.1073/pnas.1522469113

The dominant cause of malaria in Malaysia is now Plasmodium knowlesi, a zoonotic parasite of cynomolgus macaque monkeys found throughout South East Asia. Comparative genomic analysis of parasites adapted to in vitro growth in either cynomolgus or human RBCs identified a genomic deletion that includes the gene encoding normocyte-binding protein Xa (NBPXa) in parasites growing in cynomolgus RBCs but not in human RBCs. Experimental deletion of the NBPXa gene in parasites adapted to growth in human RBCs (which retain the ability to grow in cynomolgus RBCs) restricted them to cynomolgus RBCs, demonstrating that this gene is selectively required for parasite multiplication and growth in human RBCs. NBPXa-null parasites could bind to human RBCs, but invasion of these cells was severely impaired. Therefore, NBPXa is identified as a key mediator of P. knowlesi human infection and may be a target for vaccine development against this emerging pathogen.