Genetic diversity of transmission-blocking vaccine candidates Pvs25 and Pvs28 in Plasmodium vivax isolates from Yunnan Province, China

We sequenced the coding regions of pvs25 and pvs28 from 30 P. vivax isolates from Yunnan Province, identifying five amino acid haplotypes of Pvs25 and seven amino acid haplotypes of Pvs28. Among a total of four mutant residues, the predominant haplotype of Pvs25 only had the I130T substitution. For Pvs28, a total of eight amino acid substitutions were identified. The predominant haplotype of Pvs28 had two substitution at positions 52 (M52L) and 140 (T140S) with 5-6 GSGGE/D tandem repeats at the end of fourth EGF-like domain. Most amino acid substitutions were common with previous reports from South Asian isolates. Although the nucleotide diversity of pvs28 (π = 0.0034 ± 0.0012) was significantly higher than pvs25 (π = 0.0013 ± 0.0009), it was still conserved when compared with the blood stage vaccine candidates.Genetic analysis revealed limited genetic diversity of pvs25 and pvs28, suggesting antigenic diversity may not be a particular problem for Sal I based TBVs in most P. vivax-endemic areas of China.Plasmodium vivax, the most widespread species of human malaria parasites, is responsible for the majority of malaria cases outside of Africa, and the most prevalent form of relapsing malaria. Although not as lethal as P. falciparum malaria, P. vivax has caused substantial morbidity for human populations residing in Asia and South America [1,2]. Throughout the malaria control history, P. vivax malaria has displayed tremendous resilience to control efforts, which is in part due to two biological characteristics of this parasite. One is the formation of hypnozoites in the liver, which is responsible for relapses of the disease. The other is that P. vivax undergoes gametocytogenesis before manifestation of the disease symptoms, making transmission possible before treatment.P. vivax is the predominant Plasmodium species in China, and in recent years, P. vivax cases accounted for more than 90% of all malaria cases [3]. As The Ministry of Health of China has set the goal of