Characterizing the genetic diversity of the monkey malaria parasite Plasmodium cynomolgi

Abstract

Plasmodium cynomolgi is a malaria parasite that typically infects Asian macaque monkeys, and humans on rare occasions. P. cynomolgi serves as a model system for the human malaria parasite Plasmodium vivax, with which it shares such important biological characteristics as formation of a dormant liver stage and a preference to invade reticulocytes. While genomes of three P. cynomolgi strains have been sequenced, genetic diversity of P. cynomolgi has not been widely investigated. To address this we developed the first panel of P. cynomolgi microsatellite markers to genotype eleven P. cynomolgi laboratory strains and 18 field isolates from Sarawak, Malaysian Borneo. We found diverse genotypes among most of the laboratory strains, though two nominally different strains were found to be genetically identical. We also investigated sequence polymorphism in two erythrocyte invasion gene families, the reticulocyte binding protein and Duffy binding protein genes, in these strains. We also observed copy number variation in rbp genes.

Keywords: Evolution; Genetic variation; Microsatellite repeats; Plasmodium cynomolgi; Plasmodium vivax.

Figure 1. Geographical origins of P. cynomolgi strains

Strain name, aliases, and year of isolation are shown. Blue, red, and grey markers indicate specific, approximate, and dubious origins respectively, gleaned from the literature (see Supplementary Materials for references). The reported Sulawesi (Celebes) origin for the Smithsonian strain is dubious because the island lies outside of the range of the host monkey species Macaca speciosa. Asterisk (*) indicates that the site was the shipping point of the host monkey, but the location of capture of the monkey is unknown. A star shows the location of Kapit Town in Malaysian Borneo, where P. cynomolgi field isolates genotyped in this paper were collected.

Figure 2. Dendrogram showing inter-isolate differentiation based on concatenated P. cynomolgi nucleotide sequences from four genes

Dendrogram based on distance matrices from 8031 bp of concatenated nucleotide sequence of rbp1a, rbp3, and dbp1 from eight P. cynomolgi strains and five P. vivax reference strains built by Neighbor Joining with 1000 bootstraps using the HKY substitution model. The numbers shown along nodes represent bootstrap values. Identical topology was obtained using Maximum Likelihood (not shown).