Genetic diversity of circumsporozoite protein in Plasmodium knowlesi isolates from Malaysian Borneo and Peninsular Malay
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Malaria Journal Open Access
RESEARCH
Genetic diversity of circumsporozoite protein in Plasmodium knowlesi isolates from Malaysian Borneo and Peninsular Malaysia Eric Tzyy Jiann Chong1, Joveen Wan Fen Neoh2, Tiek Ying Lau2, Yvonne Ai‑Lian Lim3,4, Hwa Chia Chai5, Kek Heng Chua5 and Ping‑Chin Lee1*
Abstract Background: 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. 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. Methods: A 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 Malay‑ sia. 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. Results: The phylogenetic analysis revealed indistinguishable clusters of P. knowlesi isolates across different geo‑ graphic regions, including Malaysian Borneo and Peninsular Malaysia. Nucleotide analysis showed that the csp nonrepeat 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. Conclusions: The csp non-repeat regions are relatively conserved and there is no distinct cluster of P. knowlesi iso‑ lates 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. Keywords: Plasmodium knowlesi, Circumsporozoite protein, genetic diversity, Malaysian Borneo Background Malaria in humans is caused by Plasmodium species, including Plasmodium vivax, Plasmodium ovale spp., Plasmodium malariae, Plasmodium falciparum, and *Correspondence: [email protected] 1 Biotechnology Programme, Faculty of Science and Natural Resources, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, Malaysia Full list of author information is available at the end of the article
Plasmodium knowlesi. Plasmodium parasites also infect crab-eating macaque (Macaca fascicularis), also known as the long-tailed macaque, and southern pigtailed macaque (Macaca nemestrina). Thus, 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.
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