High genetic and haplotype diversity in vaccine candidate but not among malaria-infected children in Ibadan, Nigeria.

Malaria remains a global public health challenge. The disease has a great impact in sub-Saharan Africa among children under five years of age and pregnant women. Malaria control programs targeting the parasite and mosquitoes vectors with combinational therapy and insecticide-treated bednets are becoming obsolete due to the phenomenon of resistance, which is a challenge for reducing morbidity and mortality. Malaria vaccines would be effective alternative to the problem of parasite and insecticide resistance, but focal reports of polymorphisms in malaria candidate antigens have made it difficult to design an effective malaria vaccine. Therefore, studies geared towards elucidating the polymorphic pattern and how genes targeted for vaccine design evolve are imperative. We have carried out molecular and genetic analysis of two genes encoding vaccine candidates-the cell traversal ookinetes and sporozoites () and reticulocyte binding protein 5 () in parasite isolates from malaria-infected children in Ibadan, Nigeria to evaluate their genetic diversity, relatedness and pattern of molecular evolution. and genes were amplified from positive samples. Amplified fragments were purified and sequenced using the chain termination method. Post-sequence edit of fragments and application of various population genetic analyses was done. We observed a higher number of segregating sites and haplotypes in the than in gene, the former also presenting higher haplotype (0.942) and nucleotide diversity ( = 0.01219 and  = 0.01148). In contrast, a lower haplotype (0.426) and nucleotide diversity ( = 0.00125;  = 0.00095) was observed in the gene. Neutrality tests do not show deviation from neutral expectations for , with the circulation of multiple low frequency haplotypes (Tajima's = -0.21637; Fu and Li's = -0.08164; Fu and Li's = -0.14051). Strong linkage disequilibrium was observed between variable sites, in each of the genes studied. We postulate that the high diversity and circulation of multiple haplotypes has the potential of making a -subunit vaccine ineffective, while the low genetic diversity of gene substantiates its evolutionary conservation and potential as a malaria vaccine candidate.