Genetic polymorphism of circumsporozoite protein of Plasmodium falciparum isolates in children in Brazzaville, Republic of Congo

The first WHO-approved malaria vaccines (RTS, S/AS01, and R21/Matrix M) target part of the Plasmodium falciparum circumsporozoite protein (PfCSP), displays a degree of polymorphism that may raise concerns about vaccine efficacy. As a prelude to vaccine implementation, the study here reports investigation on Pfcsp gene polymorphisms in isolates from Congolese individuals in the Republic of Congo. Blood samples were collected from 202 children infected with P. falciparum during a cross-sectional study from March to October 2021. The full-length Pfcsp gene was amplified by nested PCR and sequenced using the Oxford Nanopore platform. Overall, 30 haplotypes were identified in the N-terminal region of the protein. The A98G mutation was the most frequent (25.6%), while KLKQP was the most conserved motif. In the central repeat region, 50 haplotypes were found, with a predominance of the NANP motif, although some haplotypes contained the NVDP, NEDP and NVNP variants. C-terminal region was highly polymorphic, with 76 haplotypes identified among the 174 sequenced samples. In the C-terminal Th2R region, the major mutations identified included K317E (87.4%) and N321K (83.9%), with a nucleotide diversity of π = 0.16. In the Th3R region, the E357Q (75.9%) mutation was predominant, with a nucleotide diversity of π = 0.08. Neutrality tests revealed contrasting patterns of evolution between the Th2R and Th3R regions. This study provides baseline data on Pfcsp genetic diversity in a defined area of the Republic of Congo. The results highlight the degree of variation in natural parasite populations at gene loci relevant to vaccine-targeted epitopes of (PfCSP) antigen. Further research incorporating immunological data will be needed to conduct in-depth assessments of vaccine efficacy.