Genetic polymorphism and natural selection of circumsporozoite protein in Myanmar Plasmodium vivax

Abstract

Background: Circumsporozoite surface protein (CSP) of malaria parasites has been recognized as one of the leading vaccine candidates. Clinical trials of vaccines for vivax malaria incorporating Plasmodium vivax CSP (PvCSP) have demonstrated their effectiveness in preventing malaria, at least in part. However, genetic diversity of PvCSP in the natural population is still a major concern.Methods: A total of 171 blood samples collected from patients infected with Plasmodium vivax in Myanmar analysed in this study. The gene for PvCSP was amplified by polymerase chain reaction, followed by T&A cloning and sequencing. Polymorphic characteristics and natural selection of Myanmar PvCSP population in Myanmar were analysed using DNASTAR, MEGA6 and DnaSP programs. The polymorphic pattern and natural selection of publicly accessible global PvCSP sequences were also comparatively analysed.Results: Myanmar PvCSP sequences were divided into two subtypes VK210 and VK247 comprising 143 and 28 sequences, respectively. The VK210 subtypes showed higher levels of genetic diversity and polymorphism than the VK247 subtypes. The N-terminal non-repeat region of PvCSP displayed limited genetic variations in the global population. Different patterns of octapeptide insertion (ANKKAEDA in VK210 and ANKKAGDA in VK247) and tetrapeptide repeat motif (GGNA) were identified in the C-terminal region of global PvCSP population. Meanwhile, the central repeat region (CRR) of Myanmar and global PvCSP, both in VK210 and VK247 variants, was highly polymorphic. The high level of genetic diversity in the CRR has been attributed to the different numbers, types and combinations of peptide repeat motifs (PRMs). Interestingly, 27 and 5 novel PRMs were found in Myanmar VK210 and VK247 variants, respectively.Conclusion: Comparative analysis of the global PvCSP population suggests a complex genetic profile of PvCSP in the global population. These results widen understanding of the genetic make-up of PvCSP in the global P. vivax population and provide valuable information for the development of a vaccine based on PvCSP.

Genetic characterization of Plasmodium vivax isolates from Pakistan using circumsporozoite protein (pvcsp) and merozoite surface protein-1 (pvmsp-1) genes as genetic markers

“…In the present study, the genetic polymorphism in the pvcsp and pvmsp-1 genes were studied in detail. The results of the study support the findings of the previously published data showing that VK210 strain is predominant type with the prevalence rate ranging between 56-100% in Iran [20,24], Myanmar [15,40], Brazil [39], India [14,49], Thailand [41,42], Azerbaijan [19], China [13,42] and Mexico [43]. There are only few malaria endemic areas where VK247 isolates are commonly present [39].…”

“…The analysis of CRR region of Pakistani pvcsp isolates is indicative of positive selection when compared with pvcsp isolates of Iran and India. The negative Tajima's D values of Myanmar pvcsp population imply purifying negative selection [15]. The evidence from the previous studies has reported that the arrangements and numbers of PRMs in CRR are indicative of occurrence of phenomenon of natural selection on the pvcsp isolates [15,45,46].…”

“…Genetic sequences of pvcsp and pvmsp-1 are being used to understand the genetic diversity [11][12][13]. The pvcsp is a highly immunogenic sporozoite surface protein, hence a good vaccine candidate, is encoded by single copy gene [8] and comprises of a central repeat domain that varies across Plasmodium species having two non-repetitive domains at N-and C-terminals [14,15]. The varying degree of number of peptides in the central repeat region reveals three variants of P. vivax namely VK210, VK247, P. vivax-like [16,17].…”

Genetic Characterization of Plasmodium vivax Isolates from Pakistan Using Circumsporozoite Protein (PvCSP) and Merozoite Surface Protein-1 (PvMSP-1) genes as genetic markers 

“…The analysis of CRR region of Pakistani PvCSP isolates is indicative of positive selection when compared with PvCSP isolates of Iran and India. The negative Tajima's D values of Myanmar PvCSP population imply purifying negative selection [15]. The evidence from the previous studies has reported that the arrangements and numbers of PRMs in CRR are indicative of occurrence of phenomenon of natural selection on the PvCSP isolates [45,46].…”

“…Genetic sequences of PvCSP and PvMSP-1 are being used to understand the genetic diversity [11][12][13]. PvCSP, a highly immunogenic sporozoite surface protein, hence a good vaccine candidate, is encoded by single copy gene [8] and comprises of a central repeat domain that varies across Plasmodium species having two non-repetitive domains at N-and C-terminals [14,15]. The varying degree of number of peptides in the central repeat region reveals three variants of P. vivax namely VK210, VK247, P. vivax-like [16,17].…”