Genetic polymorphism of circumsporozoite protein of Plasmodium falciparum among Chinese migrant workers returning from Africa to Henan Province

Abstract

Background: Plasmodium falciparum malaria is recognized as a major global public health problem. The malaria vaccine was important because the case fatality rate of falciparum malaria was high. Plasmodium falciparum circumsporozoite protein (PfCSP) is one of the potential vaccine candidates, but the genetic polymorphism of PfCSP raises concerns regarding the efficacy of the vaccine. This study aimed to investigate the genetic polymorphism of PfCSP and provide data for the improvement of PfCSP-based vaccine (RTS,S malaria vaccine).

Methods: Blood samples were collected from 287 Chinese migrant workers who were infected with P. falciparum and returning from Africa to Henan Province during 2016-2018. The Pfcsp genes were analysed to estimate the genetic diversity of this parasite.

Results: The results showed that there were two mutations at the N-terminus of imported Pfcsp in Henan Province, including insertion amino acids (58.71%, 118/201) and A → G (38.81%, 78/201). The number of repeats of tetrapeptide motifs (NANP/NVDP/NPNP/NVDA) in the central repeat region ranged mainly from 39 to 42 (97.51%, 196/201). A total of 14 nonsynonymous amino acid changes were found at the C-terminus. The average nucleotide difference (K) of imported Pfcsp in Henan Province was 5.719, and the haplotype diversity (Hd) was 0.964 ± 0.004. The estimated value of dN-dS was 0.047, indicating that the region may be affected by positive natural selection. The minimum number of recombination events (Rm) of imported Pfcsp in Henan Province was close to that in Africa. The analysis of genetic differentiation showed that there may be moderate differentiation between East Africa and North Africa (Fst = 0.06484), and the levels of differentiation in the other regions were very small (Fst < 0.05).

Conclusions: The N-terminus of Pfcsp was relatively conserved, and the central repeat region and the Th2R and Th3R regions of the C-terminus were highly polymorphic. The gene polymorphism pattern among Chinese migrant workers returning from Africa to Henan Province was consistent with that in Africa. The geographical pattern of population differentiation and the evidence of natural selection and gene recombination suggested that the effect of polymorphism on the efficacy of PfCSP-based vaccines should be considered.

Keywords: Africa; Circumparzoite protein; Genetic polymorphism; Henan Province; Imported malaria; Plasmodium falciparum.

Fig. 1

A Analysis of the N-terminal polymorphism of imported PfCSP in Henan Province. Dots represent the same residue as the 3D7 reference sequence. Dashes indicate intervals to maximize alignment. The yellow shaded area represents the predicted T-cell epitope area. The underlined conserved motif (KLKQP) was involved in the invasion of spores into mosquito salivary glands and bound to hepatocytes before invasion. The number of samples refers to the frequency of each haplotype. B Polymorphism characteristics of the central repeat region of imported PfCSP in Henan Province; 1: tetrapeptide motif NANP; 2: tetrapeptide motif NVDP; 3: tetrapeptide motif NPNP; 4: tetrapeptide motif NVDA; 1 and 2 represent known tetrapeptide repeats, and yellow shaded areas 3 and 4 represent newly discovered tetrapeptide motifs

Fig. 2

Analysis of C-terminal haplotypes of imported PfCSP in Henan Province; The dots represent the same residue as the 3D7 reference sequence. The blue shaded area represents the Th2R area. The orange shaded area represents the Th3R area. The number of samples refers to the frequency of each haplotype

Fig. 3

Analysis of the C-terminal nucleotide diversity of imported PfCSP in Henan Province. The nucleotide sequences of the C-terminal nonrepeat region (amino acid sites 311 ~ 363 fragments) of imported PfCSP in Henan Province were selected. The nucleotide diversity (π) was calculated by DnaSP software with a sliding window length of 10 bp and a step size of 5 bp