Geographical origin of Plasmodium vivax in the Hainan Island, China: insights from mitochondrial genome

Background Hainan Province, China, has been an endemic region with high transmission of Plasmodium falciparum and Plasmodium vivax . Indigenous malaria caused by P. vivax was eliminated in Hainan in 2011, while imported vivax malaria remains. However, the geographical origin of P. vivax cases in Hainan remains unclear. Methods Indigenous and imported P. vivax isolates (n = 45) were collected from Hainan Province, and the 6 kb mitochondrial genome was obtained. Nucleotide ( π ) and haplotype ( h ) diversity were estimated using DnaSP. The numbers of synonymous nucleotide substitutions per synonymous site ( d S ) and nonsynonymous nucleotide substitutions per nonsynonymous site ( d N ) were calculated using the SNAP program. Arlequin software was used to estimate the genetic diversity index and assess population differentiation. Bayesian phylogenetic analysis of P. vivax was performed using MrBayes. A haplotype network was generated using the NETWORK program. Results In total, 983 complete mitochondrial genome sequences were collected, including 45 from this study and 938 publicly available from the NCBI. Thirty-three SNPs were identified, and 18 haplotypes were defined. The haplotype (0.834) and nucleotide (0.00061) diversity in the Hainan populations were higher than China’s Anhui and Guizhou population, and the majority of pairwise F ST values in Hainan exceeded 0.25, suggesting strong differentiation among most populations except in Southeast Asia. Most Hainan haplotypes were connected to South/East Asian and China’s others haplotypes, but less connected with populations from China's Anhui and Guizhou provinces. Mitochondrial lineages of Hainan P. vivax belonged to clade 1 of four well-supported clades in a phylogenetic tree, most haplotypes of indigenous cases formed a subclade of clade 1, and the origin of seven imported cases (50%) could be inferred from the phylogenetic tree, but five imported cases (42.8%) could not be traced using the phylogenetic tree alone, necessitating epidemiological investigation. Conclusions Indigenous cases in Hainan display high genetic (haplotype and nucleotide) diversity. Haplotype network analysis also revealed most haplotypes in Hainan were connected to the Southeast Asian populations and divergence to a cluster of China’s other populations. According to the mtDNA phylogenetic tree, some haplotypes were shared between geographic populations, and some haplotypes have formed lineages. Multiple tests are needed to further explore the origin and expansion of P. vivax populations.