Restricted genetic heterogeneity of the Plasmodium vivax transmission-blocking vaccine (TBV) candidate Pvs48/45 in a low transmission setting: Implications for the Plasmodium vivax malaria vaccine development

Genetic polymorphisms of Plasmodium vivax transmission-blocking vaccine candidates Pvs48/45 and Pvs47 in Thailand

BACKGROUND

The genetic diversity of malaria parasites varies between regions in the world. The genetic polymorphisms of the genes Pvs48/45 and Pvs47 which encode gametocyte/gamete proteins of Plasmodium vivax, were studied because of their potential as transmission-blocking vaccine (TBV) targets. The aim of the present study was to investigate the genetic diversity of Pvs48/45 and Pvs47 in clinical isolates from endemic areas of Thailand.

METHODS

Plasmodium vivax samples collected from four provinces neighbouring either Myanmar or Malaysia were analysed using polymerase chain reaction and nucleotide sequencing.   RESULTS: Fifteen and 18 amino acid substitutions were observed in 36 Pvs48/45 and 62 Pvs47 deduced amino acid sequences, respectively. Eleven haplotypes were identified in Pvs48/45 and 26 in Pvs47. Overall, low nucleotide diversities were observed for Pvs48/45 (π = 0.00104) and Pvs47 (π = 0.00321). Tajima's D, and Fu and Li's D* and F* values were negative for both genes, Pvs48/45 and Pvs47 while a significant difference was found in Pvs48/45 (P < 0.05).

CONCLUSION

The limited polymorphism of the two investigated TBV candidate antigens observed in this study is consistent with findings in worldwide isolates. The collected genetic diversity data could be helpful for developing effective TBVs in malaria-endemic areas.

Towards Eradication of Malaria: Is the WHO's RTS,S/AS01 Vaccination Effective Enough?

BACKGROUND

Recent advances in mosquito eradication and antimalarial treatments have reduced the malaria burden only modestly. An effective malaria vaccine remains a high priority, but its development has several challenges. Among many potential candidates, the RTS,S/AS01 vaccine (MosquirixTM) remains the leading candidate.

OBJECTIVE AND METHOD

This review aims to understand the advances in the RTS,S/AS01 vaccine, and future comments regarding the vaccine's effectiveness in malaria eradication. Literature review for the past five decades was performed searching PubMed, EMBASE Ovid, and Cochrane Library, with using the following search items: ("malaria" OR "WHO's malaria" OR "Plasmodium falciparum" OR "RTS,S" OR "RTS,S/AS01" OR "RTS,S/AS02" OR "pre-erythrocytic malaria" OR "circumsporozoite" OR "Mosquirix") AND ("vaccine" OR "vaccination").

RESULTS

RTS,S/AS01, a recombinant pre-erythrocytic vaccine containing Plasmodium falciparum surface-protein (circumsporozoite) antigen, is safe, well-tolerated, and immunogenic in children. Three doses, along with a booster, have a modest efficacy of about 36% in children (age 5-17 months) and about 26% in infants (age 6-12 weeks) against clinical malaria during a 48-month follow-up. However, the efficacy varies among population subgroups and with the parasite strain, it reduces without a booster and offers protection for a limited duration. Because of its potential cost-effectiveness and positive public health effect, the vaccine is being investigated in a pilot program for mortality benefits and broader deployment.

CONCLUSION

The RTS,S/AS01 vaccine prevents malaria; however, it should be considered another addition to the malaria-control program and not as an eradication tool because of its relatively low to modest efficacy.