Assessment of genetic diversity of Plasmodium falciparum circumsporozoite protein in Sudan: the RTS,S leading malaria vaccine candidate

Malaria Journal

Yassir Osman Mohammed¹  Lubna Taj Elssir¹  Mohammed-Ahmed B. Elnour¹  Omnia Altahir¹  Nouh Saad Mohamed²  Mustafa Abubakr³  Ahad R. Elsadig⁴  Mohamed S. Ali⁵  Yousif Ali⁶  Hanadi AbdElbagi⁷  Abdalla Elssir Ahmed⁷  Ayman Ahmed⁷  Emmanuel Edwar Siddig⁸  Rihab Ali Omer⁹ 

[1] Department of Parasitology and Medical Entomology, Tropical Medicine Research Institute, National Centre for Research, Khartoum, Sudan;Department of Parasitology and Medical Entomology, Tropical Medicine Research Institute, National Centre for Research, Khartoum, Sudan;Molecular Biology Unit, Sirius Training and Research Centre, Khartoum, Sudan;Department of the Integrated Vector Management (IVM), Federal Ministry of Health, Khartoum, Sudan;El-Raqi Hospital, National University, Khartoum, Sudan;Faculty of Medicine, EL-Neelain University, Khartoum, Sudan;Health Emergencies and Epidemics Control General Directorate, Sudan Federal Ministry of Health, Khartoum, Sudan;Molecular Biology Unit, Sirius Training and Research Centre, Khartoum, Sudan;Mycetoma Research Center, University of Khartoum, Khartoum, Sudan;Pediatric Epidemiology, Clinic and Polyclinic for Child and Adolescent Medicine, Medical Faculty, University of Leipzig, Leipzig, Germany;

关键词: Malaria;    Plasmodium falciparum;    Vaccine;    RTS,S;    Hapd;    N-terminal, central repeats, and C-terminal regions;   

DOI  :  10.1186/s12936-021-03971-0

来源: Springer

【 摘 要 】

BackgroundThe currently used malaria vaccine, RTS,S, is designed based on the Plasmodium falciparum circumsporozoite protein (PfCSP). The pfcsp gene, besides having different polymorphic patterns, can vary between P. falciparum isolates due to geographical origin and host immune response. Such aspects are essential when considering the deployment of the RTS,S vaccine in a certain region. Therefore, this study assessed the genetic diversity of P. falciparum in Sudan based on the pfcsp gene by investigating the diversity at the N-terminal, central repeat, and the C-terminal regions.MethodsA cross-sectional molecular study was conducted; P. falciparum isolates were collected from different health centres in Khartoum State between January and December 2019. During the study period, a total of 261 febrile patients were recruited. Malaria diagnosis was made by expert microscopists using Giemsa-stained thick and thin blood films. DNA samples were examined by the semi-nested polymerase chain reaction (PCR). Single clonal infection of the confirmed P. falciparum cases, were used to amplify the pfcsp gene. The amplified amplicons of pfcsp have been sequenced using the Sanger dideoxy method. The obtained sequences of pfcsp nucleotide diversity parameters including the numbers of haplotypes (Hap), haplotypes diversity (Hapd), the average number of nucleotide differences between two sequences (p), and the numbers of segregating sites (S) were obtained. The haplotype networks were constructed using the online tcsBU software. Natural selection theory was also tested on pfcsp using Fuand Li’s D, Fuand Li’s F statistics, and Tajima’s D test using DnaSP.ResultsIn comparison with the different pfcsp reference strains, the Sudanese isolates showed high similarity with other African isolates. The results of the N-terminal region showed the presence of 2 different haplotypes with a Hapd of 0.425 ± 0.00727. The presence of the unique insertion of NNNGDNGREGKDEDKRDGNN was reported. The KLKQP motif was conserved in all the studied isolates. At the central repeat region, 11 haplotypes were seen with a Hapd of 0.779 ± 0.00097. The analysis of the genetic diversity in the C-terminal region showed the presence of 10 haplotypes with a Hapd of 0.457 ± 0.073. Several non-synonymous amino acids changes were also seen at the Th2R and the Th3R T-cell epitope regions including T317K, E317K, Q318E, K321N, I322K, T322K, R322K, K324Q, I327L, G352N, S354P, R355K, N356D, Q357E, and E361A.ConclusionsIn this study, the results indicated a high conservation at the pfcsp gene. This may further contribute in understanding the genetic polymorphisms of P. falciparum prior to the deployment of the RTS,S vaccine in Sudan.

【 授权许可】

CC BY