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Background Accurate diagnosis of Plasmodium infection is crucial for prompt malaria treatment and surveillance. Microscopic examination has been widely applied as the gold standard for malaria diagnosis in most part of malaria endemic areas, but its diagnostic value has been questioned, particularly in submicroscopic malaria. In this study, the diagnostic performance of microscopic examination and nested polymerase chain reaction (PCR) was evaluated to establish optimal malaria diagnosis method in Myanmar. Methods A total of 1125 blood samples collected from residents in the villages and towns located in Naung Cho, Pyin Oo Lwin, Tha Beik Kyin townships and Mandalay of Upper Myanmar were screened by microscopic examination and species-specific nested PCR method. Results Among the 1125 blood samples, 261 samples were confirmed to be infected with malaria by microscopic examination. Evaluation of the 1125 samples by species-specific nested PCR analysis revealed that the agreement between microscopic examination and nested PCR was 87.3% (261/299). Nested PCR successfully detected 38 Plasmodium falciparum or Plasmodium vivax infections, which were missed in microscopic examination. Microscopic examinations also either misdiagnosed the infected Plasmodium species, or did not detect mixed infections with different Plasmodium species in 31 cases. Conclusions The nested PCR method is more reliable than conventional microscopic examination for the diagnosis of malaria infections, and this is particularly true in cases of mixed infections and submicroscopic infections. Given the observed higher sensitivity and specificity of nested PCR, the molecular method holds enormous promise in malaria diagnosis and species differentiation, and can be applied as an effective monitoring tool for malaria surveillance, control and elimination in Myanmar.

Background Plasmodium vivax apical membrane antigen-1 (PvAMA-1) is a leading candidate antigen for blood stage malaria vaccine. However, antigenic variation is a major obstacle in the development of an effective vaccine based on this antigen. In this study, the genetic structure and the effect of natural selection of PvAMA-1 among Korean P. vivax isolates were analysed. Methods Blood samples were collected from 66 Korean patients with vivax malaria. The entire PvAMA-1 gene was amplified by polymerase chain reaction and cloned into a TA cloning vector. The PvAMA-1 sequence of each isolate was sequenced and the polymorphic characteristics and effect of natural selection were analysed using the DNASTAR, MEGA4, and DnaSP programs. Results Thirty haplotypes of PvAMA-1, which were further classified into seven different clusters, were identified in the 66 Korean P. vivax isolates. Domain II was highly conserved among the sequences, but substantial nucleotide diversity was observed in domains I and III. The difference between the rates of non-synonymous and synonymous mutations suggested that the gene has evolved under natural selection. No strong evidence indicating balancing or positive selection on PvAMA-1 was identified. Recombination may also play a role in the resulting genetic diversity of PvAMA-1. Conclusions This study is the first comprehensive analysis of nucleotide diversity across the entire PvAMA-1 gene using a single population sample from Korea. Korean PvAMA-1 had limited genetic diversity compared to PvAMA-1 in global isolates. The overall pattern of genetic polymorphism of Korean PvAMA-1 differed from other global isolates and novel amino acid changes were also identified in Korean PvAMA-1. Evidences for natural selection and recombination event were observed, which is likely to play an important role in generating genetic diversity across the PvAMA-1. These results provide useful information for the understanding the population structure of P. vivax circulating in Korea and have important implications for the design of a vaccine incorporating PvAMA-1.

Background Plasmodium vivax re-emerged in 1993. Although the number of infections has been steadily decreasing, it is likely to continue to affect public health until it is eradicated. The aim of this study is to measure anti-circumsporozoite protein (CSP) antibody and compare malaria prevalence. As to understand the prevalence, an epidemiology study has to be conducted in the Republic of Korea. Methods A total of 1,825 and 1,959 blood samples were collected in 2010 and 2011, respectively, from the inhabitants of Ganghwa and Cheorwon counties. The antibody titers of the inhabitants were measured by enzyme-linked immunosorbent assay (ELISA) using recombinant protein purified from Escherichia coli transformed with a CSP gene-inserted pET-28a(+) expression vector. Microscopic examination was performed to identify malaria parasites. Results The annual parasite incidence (API) in Ganghwa decreased from 4.28 in 2010 to 2.23 in 2011, and that in Cheorwon decreased from 1.88 in 2010 to 1.15 in 2011. The antibody-positive CSP rate in these areas also decreased from 18.14% (331/1825) in 2010 to 15.36% (301/1959) in 2011. Pearson analysis showed a strong correlation between the API and the antibody-positive CSP rate in these areas (r = 1.000, P

Background Transmission-blocking vaccines (TBVs), which target the sexual stages of malaria parasites to interfere with and/or inhibit the parasite’s development within mosquitoes, have been regarded as promising targets for disrupting the malaria transmission cycle. In this study, genetic diversity of four TBV candidate antigens, Pvs25, Pvs28, Pvs48/45, and PvWARP, among Plasmodium vivax Korean isolates was analysed. Methods A total of 86 P. vivax- infected blood samples collected from patients in Korea were used for analyses. Each of the full-length genes encoding four TBV candidate antigens, Pvs25, Pvs28, Pvs48/45, and PvWARP, were amplified by PCR, cloned into T&A vector, and then sequenced. Polymorphic characteristics of the genes were analysed using the DNASTAR, MEGA4, and DnaSP programs. Results Polymorphism analyses of the 86 Korean P. vivax isolates revealed two distinct haplotypes in Pvs25 and Pvs48/45, and three different haplotypes in PvWARP. In contrast, Pvs28 showed only a single haplotype. Most of the nucleotide substitutions and amino acid changes identified in all four TBV candidate antigens were commonly found in P. vivax isolates from other geographic areas. The overall nucleotide diversities of the TBV candidates were much lower than those of blood stage antigens. Conclusions Limited sequence polymorphisms of TBV candidate antigens were identified in the Korean P. vivax population. These results provide baseline information for developing an effective TBV based on these antigens, and offer great promise for applications of a TBV against P. vivax infection in regions where the parasite is most prevalent.

Background After the re-emergence of Plasmodium vivax in 1993, a total of 31,254 cases of vivax malaria were reported between 1993–2012 in the Republic of Korea (ROK). The purpose of this study was to review Korea Centers for Disease Control and Prevention records to investigate the transmission of malaria from 2010–2012. Methods Reporting of microscopy-diagnosed cases of malaria is mandatory in the ROK. In this study, all available records of malaria cases and malaria vectors collected from 2010 – 2012 in Cheorwon County, Gangwon Province and Ganghwa County, Incheon Metropolitan City, were reviewed. Results Although the number of cases of malaria peaked a third time in 2010 (1,772 cases) since the re-emergence of P. vivax, the incidence decreased two-fold to 838 in 2011 and three-fold to 555 in 2012. The number of cases decreased 52.7% in 2011 compared with that in 2010 and 33.8% in 2012 compared with that in 2011. However, the number of cases increased in Incheon Metropolitan City (15.3%) and Gyeongnam Province (23.1%) in 2012 compared with 2011. Of the 3,165 cases of vivax malaria in 2010–2012, 798 (25.2%) were in ROK military personnel, 519 (16.4%) in veterans, and 1,848 (58.4%) in civilians. In total, there were 2,666 male patients and 499 female patients, and the ratio of female to male patients increased from 1:7.9 in 2011 to 1:4.1 in 2012. Conclusions A rapid decrease in the incidence of malaria was observed in most areas from 2010 to 2012, but the incidence increased again in the western part of the demilitarized zone. Therefore, more intensive surveillance is needed throughout high risk areas to identify factors responsible for increase/decrease in the incidence of malaria in the ROK.

Background: The merozoite surface protein-3 beta of Plasmodium vivax (PvMSP-3 beta) is one of the candidate antigens for blood stage malaria vaccine development. The polymorphisms in PvMSP-3 beta have been reported in certain P. vivax isolates. However, the diversity of PvMSP-3 beta throughout its global distribution has not been well understood. In this study, the genetic diversity and the effects of natural selection in PvMSP-3 beta among P. vivax Korean isolates were analysed. Methods: Blood samples were collected from 95 patients with vivax malaria in Korea. The region flanking full-length PvMSP-3 beta was amplified by polymerase chain reaction and cloned into a TA cloning vector. The PvMSP-3 beta sequence of each isolate was determined and the polymorphic characteristics and effects of natural selection were analysed using the DNASTAR, MEGA4, and DnaSP programs. Results: Five different subtypes of PvMSP-3 beta were identified based on single nucleotide polymorphisms (SNPs), insertions, and deletions. Although a high level of sequence diversity was observed in the PvMSP-3 beta gene, the coiled-coil tertiary structure of the PvMSP-3 beta protein was well conserved in all of the sequences. The PvMSP-3 beta of Korean isolates is under natural selection. DNA polymerase slippage and intragenic recombination likely contributed to PvMSP-3 beta diversity in Korean P. vivax isolates. Conclusions: The PvMSP-3 beta of Korean P. vivax isolates displayed polymorphisms, with SNPs, insertions and deletions scattered throughout of the gene. These results of parasite heterogeneity are relevant to the development of a PvMSP-3 beta based vaccine against P. vivax and the implementation of malaria control programmes in Korea.