Abstract
BackgroundUnderstanding the genetic diversity of candidate genes for malaria vaccines such as circumsporozoite protein (csp) may enhance the development of vaccines for treating Plasmodium knowlesi. Hence, the aim of this study is to investigate the genetic diversity of non-repeat regions of csp in P. knowlesi from Malaysian Borneo and Peninsular Malaysia.MethodsA total of 46 csp genes were subjected to polymerase chain reaction amplification. The genes were obtained from P. knowlesi isolates collected from different divisions of Sabah, Malaysian Borneo, and Peninsular Malaysia. The targeted gene fragments were cloned into a commercial vector and sequenced, and a phylogenetic tree was constructed while incorporating 168 csp sequences retrieved from the GenBank database. The genetic diversity and natural evolution of the csp sequences were analysed using MEGA6 and DnaSP ver. 5.10.01. A genealogical network of the csp haplotypes was generated using NETWORK ver. 4.6.1.3.ResultsThe phylogenetic analysis revealed indistinguishable clusters of P. knowlesi isolates across different geographic regions, including Malaysian Borneo and Peninsular Malaysia. Nucleotide analysis showed that the csp non-repeat regions of zoonotic P. knowlesi isolates obtained in this study underwent purifying selection with population expansion, which was supported by extensive haplotype sharing observed between humans and macaques. Novel variations were observed in the C-terminal non-repeat region of csp.ConclusionsThe csp non-repeat regions are relatively conserved and there is no distinct cluster of P. knowlesi isolates from Malaysian Borneo and Peninsular Malaysia. Distinctive variation data obtained in the C-terminal non-repeat region of csp could be beneficial for the design and development of vaccines to treat P. knowlesi.
Highlights
Understanding the genetic diversity of candidate genes for malaria vaccines such as circumsporozo‐ ite protein may enhance the development of vaccines for treating Plasmodium knowlesi
A distinct cluster was observed for outgroups, and the P. knowlesi isolates were genetically closer to Plasmodium coatneyi based on the non-repeat csp sequence
The nucleotide alignment of the csp in this study showed that the average number of pairwise nucleotide differences (K) was 8.958
Summary
Understanding the genetic diversity of candidate genes for malaria vaccines such as circumsporozo‐ ite protein (csp) may enhance the development of vaccines for treating Plasmodium knowlesi. Malaria is considered an emerging zoonotic disease Humans may acquire these parasites when they are close to the habitats of macaques infected with the parasites through anopheline mosquito vectors in forests. Chong et al Malar J (2020) 19:377 that 228 million new malaria cases and 405,000 deaths from malaria occurred around the world in 2018 [1]. These data are at odds with the vision set by the World Health Organization in early 2015, which has a goal of at least a 90% reduction of the global malaria incidence and mortality rates by 2030 [2]
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