| Malaria constitutes a major human health threat caused by infection with protozoan parasites of the genus Plasmodium. P. vivax represents the most widespread malaria parasite in the world. Malaria also remains one of the leading parasite diseases in China, located in 18 provinces / autonomous regions / municipalities with a coverage of 0. 53 billion population. As the relaping behaving of vivax malaria process and parasite strains resistant to anti - malarial drugs as well as mosquito vectors resistant to insecticides have emerged, new approaches for malaria control are badly needed and intensive research efforts have gone to develop malaria vaccines.Although different complementary approaches to vaccine development are being undertaken in several laboratories, the major obstacle confronting the development of an effective malaria vaccine is the extensive antigenic diversity in natural populations of malaria parasites. Transmission - blocking vaccines (TBVs ) are becoming more attractive because of their limited genetic polymorphism. Pys25 is the ooki-nete surface protein, which plays a role in ookinete survival in the mosquito midgut. Some results have indicated that Pvs25 can be the leading vivax malaria TBV candidate.Although these efforts have been undergone for Pvs25, the data is still limited not enough to identify the feasibility for the application of this kind of TBV. Some results have suggested that the polymorphism of target antigen exists among field isolates, even single amino acidsubstitution can change the primary structure of parasite antigen. This may have an adverse impact on the efficacy of vaccines application. Therefore, it is necessary to acquire the evaluation of the pre - existing polymorphism in Pvs25 before applying it to the vivax malaria endemic regions. Otherwise, P. vivax is popular in extensive areas of China, but there is no report to be published about this study. For these purposes, we provided a detailed analysis of the diversity about this malaria vaccine candidate antigen isolates from Hubei and Zhe-jiang province of China and compared it with parasite population from Bangladesh, which would apply a necessary basic data for the development and application of TBVs against malaria.MATERIALS AND METHODSThe parasite DNA used for the genetic polymorphism assay was obtained from dried filter paper blood spots as described by Sakihama and others. The blood samples were from 45 P. vivax infecting patients during malaria transmission season. As a positive control, ge-nomic DNA extracted from P. vivax Sal 1 strain was used. The genes were PCR amplified and the amplified products were purified, cloned, and sequenced. Both strands were sequenced from at least two clones from two independent PCR amplifications. Computer - based algorithms were used to analyze neucleotide and amino acid sequences and the sequence alignments were done with Mac Vector software. Intrap-opulation and interpopulation diversity indexes were calculated by u-sing DnaSP software.RESULTS1. The Pvs25 gene sequence for 646 nucleotides codes 215 amino acids, which include the complete Pvs25 sequence.2. Three non - synonymous mutations ( G/C289, T/C389, C/ A391) and no synonymous mutations were identified, which were the same with precious report.3. Two conserved (E/Q97, Q/K131) and one half - conserved (I/T130) amino acid substitutions were identified. E/Q97 was located in the second EGF - like domain of Pvs25, while I/T130 and Q/ K131 were located in the third one. The mutation (C/A391) produce the amino acid substitution (Q/K131) , which was only found in Bangladesh isolates.4. These polymorphic nucleotides generated a total of 4 haplo-types (G289-C38-C391,C289-C389- C391,G289-C389-A 391,C289-C389 - A391 ) among the 45 sequences. Haplotypes G289 - C389 - C391 from Chinese isolates was not preciously reported and can be considered predominant in China whose frequency was 80. 6% .5. The nucleotide diversity () in the China samples was 0. 00050, compared to 0. |
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