Abstract
BackgroundPlasmodium knowlesi is one of the monkey malaria parasites that can cause human malaria. The Duffy binding protein of P. knowlesi (PkDBPαII) is essential for the parasite’s invasion into human and monkey erythrocytes. A previous study on P. knowlesi clinical isolates from Peninsular Malaysia reported high level of genetic diversity in the PkDBPαII. Furthermore, 36 amino acid haplotypes were identified and these haplotypes could be separated into allele group I and allele group II. In the present study, the PkDBPαII of clinical isolates from the Malaysian states of Sarawak and Sabah in North Borneo was investigated, and compared with the PkDBPαII of Peninsular Malaysia isolates.MethodsBlood samples from 28 knowlesi malaria patients were used. These samples were collected between 2011 and 2013 from hospitals in North Borneo. The PkDBPαII region of the isolates was amplified by PCR, cloned into Escherichia coli, and sequenced. The genetic diversity, natural selection and phylogenetics of PkDBPαII haplotypes were analysed using MEGA5 and DnaSP ver. 5.10.00 programmes.ResultsForty-nine PkDBPαII sequences were obtained. Comparison at the nucleotide level against P. knowlesi strain H as reference sequence revealed 58 synonymous and 102 non-synonymous mutations. Analysis on these mutations showed that PkDBPαII was under purifying (negative) selection. At the amino acid level, 38 different PkDBPαII haplotypes were identified. Twelve of the 28 blood samples had mixed haplotype infections. Phylogenetic analysis revealed that all the haplotypes were in allele group I, but they formed a sub-group that was distinct from those of Peninsular Malaysia. Wright’s FST fixation index indicated high genetic differentiation between the North Borneo and Peninsular Malaysia haplotypes.ConclusionsThis study is the first to report the genetic diversity and natural selection of PkDBPαII of P. knowlesi from Borneo Island. The PkDBPαII haplotypes found in this study were distinct from those from Peninsular Malaysia. This difference may not be attributed to geographical separation because other genetic markers studied thus far such as the P. knowlesi circumsporozoite protein gene and small subunit ribosomal RNA do not display such differentiation. Immune evasion may possibly be the reason for the differentiation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0610-x) contains supplementary material, which is available to authorized users.
Highlights
Plasmodium knowlesi is one of the monkey malaria parasites that can cause human malaria
The present study found distinct differences in the PkDBPαII of North Borneo upon comparison with those from Peninsular Malaysia
Multiple alignment of the PkDBPαII amino acid sequences (Additional file 1) in this study revealed that these 12 residues were conserved in the PkDBPαII of North Borneo
Summary
Plasmodium knowlesi is one of the monkey malaria parasites that can cause human malaria. The Duffy binding protein of P. knowlesi (PkDBPαII) is essential for the parasite’s invasion into human and monkey erythrocytes. Plasmodium knowlesi, a malaria parasite of macaque monkeys, was reported to cause a large number of human infections in the Malaysian state of Sarawak, North Borneo, in 2004 [1]. Subsequent to this landmark report, human knowlesi malaria cases have been documented in in other parts of Borneo Island, Peninsular Malaysia, and in many other countries in Southeast Asia [2]. PkDBPβII and PkDBPγII, bind only to macaque erythrocytes and not to the Duffy antigen of human erythrocytes [5]
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