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

Abstract

Background The 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. Methods A 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. Results In 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. Conclusions In 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.

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

“…This result was attributed to the sample sizes [ 31 ]. Larger sample size from other different regions and the selected regions of this study might provide different results if this insertion occurs by chance in the Sudanese Pfcsp gene [ 32 ]. The N-terminal region can be an attractive component of PfCSP-based vaccine due to the N-terminus of imported Pfcsp was relatively conserved.…”

The Low Variability of Tc24 in Trypanosoma cruzi TcI as an Advantage for Chagas Disease Prophylaxis and Diagnosis in Mexico

“…The identification of the genetic variants that circulate in a region is essential in order to establish the potential efficiency of prophylactic vaccines. This was demonstrated in the currently used malaria vaccine against Plasmodium falciparum in Sudan and other African countries [ 51 ]. On the other hand, previous studies related to the evaluation of the genetic diversity of other neglected tropical parasites have provided relevant information about the strategies related to the mitigation of transmission or the effectiveness of the control, as in the case of Plasmodium vivax in the southeast of Mexico [ 52 ].…”

Blood meal profile and positivity rate with malaria parasites among different malaria vectors in Sudan

“…The chances of Anopheles to encounter the parasite in the blood meal of infected human can be very high during the peak transmission season [ 30 , 38 , 47 ]. This can affect significantly the role of vector population in transmitting malaria, such as described by Guelbéogo et al [ 47 ], who reported a high frequency of Anopheles coluzzii engorged females with human-animal mixed blood meals.…”

“…Using the semi-nested PCR, the primers used for the detection of the 4 human malaria parasites in Sudan including P. falciparum, P. vivax, Plasmodium ovale , and Plasmodium malariae were adopted from Rubio et al [ 37 ] including; UN-R: 5′ GAC GGT ATC TGA TCG TCT T 3′, UN-F: 5′ AGT GTG TAT CAA TCG AGT TT 3′, for the first PCR reaction and UN-F primer and Fal-R: 5′ AGT TCC CCT AGA ATA GTT ACA 3′, Viv-R: 5′ AGG ACT TCC AAG CCG AAG 3′, Ova-R: 5′ GCA TAA GGA ATG CAA AGA ACA G 3′, and Mal-R: 5′ GCC CTC CAA TTG CCT TCT 3′, for the second PCR reaction to confirm the presence of Plasmodium species. PCR cycling condition was adjusted according to Mohamed et al [ 38 ]. Positive DNA of P. falciparum, P. vivax, P. ovale , and P. malariae were used as positive controls in each PCR run.…”