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Initial malarial infection mostly causes symptomatic illness in humans. Infection that is not fatal induces complete protection from severe illness and death, and thus complete protection from severe illness or death is granted with sufficient exposure. However, malaria parasite immunity necessitates constant exposure. Therefore, it is important to evaluate lowered immunity and recurrent susceptibility to symptomatic disease in lower transmission areas. We aimed to investigate selection pressure based on transmission levels, antimalarial drug use, and environmental factors. We whole genome sequenced (WGS) P. falciparum clinical samples from Chinese hosts working in Ghana and compared the results with the WGS data of isolates from native Ghanaians downloaded from pf3k. The P. falciparum samples were generally clustered according to their geographic origin, and Chinese imported samples showed a clear African origin with a slightly different distribution from the native Ghanaian samples. Moreover, samples collected from two host populations showed evidence of differences in the intensity of selection. Compared with native Ghanaian samples, the China-imported isolates exhibited a higher proportion of monoclonal infections, and many genes associated with RBC invasion and immune evasion were found to be under less selection pressure. There was no significant difference in the selection of drug-resistance genes due to a similar artemisinin-based combination therapy medication profile. Local selection of malarial parasites is considered to be a result of differences in the host immunity or disparity in the transmission opportunities of the host. In China, most P. falciparum infections were imported from Africa, and under these circumstances, distinct local selective pressures may be caused by varying acquired immunity and transmission intensity. This study revealed the impact of host switching on the immune system, and it may provide a better understanding of the mechanisms that enable clinical immunity to malaria. [ABSTRACT FROM AUTHOR]

To reveal the genetic characteristics of one member of the Plasmodium falciparum repetitive interspersed family (rif), we sequenced the rif gene (PF3D7_1254800) in 53 field isolates collected from Ghana-imported cases into China and compared them with 350 publicly available P. falciparum rif sequences from global populations. In the Ghana-imported population, the nucleotide diversities were 0.05714 and 0.06616 for the full length and variable region of rif gene, respectively. Meanwhile, 22 and 20 haplotypes were identified for the full length and variable region of rif gene (Hd = 0.843 and 0.838, respectively). Diversity of rif gene in Ghana-imported population was higher than that observed in Cambodia, Thailand, Vietnam, Myanmar, Mali, Ghana, and Senegal populations. In this analysis, we found high genetic diversity of rif gene in global P. falciparum populations and identified 158 haplotypes. Tajima's D -test shows that there are large differences in the direction of selection between the conserved and variable region of rif gene. Tajima's D value for the variable region was 0.20074, indicating that balancing selection existed in this region. We found that the variable region was the main target of selection for positive diversification, and most mutation sites were located in this region. The population structure suggested optimized cluster values of K = 6. The five groups in Ghana-imported population included a unique subpopulation. Our results reveal the dynamics of the rif gene (PF3D7_1254800) in P. falciparum populations, which can aid in the rational design of P. falciparum rif -based vaccines. • Genetic polymorphism of the rif gene (PF3D7_1254800) was analyzed from global P. falciparum isolates. • Nucleotide diversity of rif gene from the 53 Ghana imported isolates was 0.05714. • Variable region of rif gene is dominant target of positive selection for Ghana imported isolates. [ABSTRACT FROM AUTHOR]