The organization and allelic recombination of the merozoite surface protein-1 gene of Plasmodium vivax (PvMsp-1), the most widely prevalent human malaria parasite, were evaluated in complete nucleotide sequences of 40 isolates from various geographic areas. Alignment of 31 distinct alleles revealed the mosaic organization of PvMsp-1, consisting of seven interallele conserved blocks flanked by six variable blocks. The variable blocks showed extensive variation in repeats and nonrepeat unique sequences. Numerous recombination sites were distributed throughout PvMsp-1, in both conserved blocks and variable block unique sequences, and the distribution was not uniform. Heterozygosity of PvMsp-1 alleles was higher in Asia (0.953 ؎ 0.009) than in Brazil (0.813 ؎ 0.047). No identical alleles were shared between Asia and Brazil, whereas all but one variable block nonrepeat sequence found in Brazil occurred in Asia. These observations suggest that P. vivax populations in Asia are ancestral to Brazilian populations, and that PvMsp-1 has heterogeneity in frequency of allelic recombination events. Recurrent origins of new PvMsp-1 alleles by repeated recombination events were supported by a rapid decline in linkage disequilibrium between pairs of synonymous sites with increasing nucleotide distance, with little linkage disequilibrium at a distance of over 3 kb in a P. vivax population from Thailand, evidence for an effectively high recombination rate of the parasite. Meanwhile, highly reduced nucleotide diversity was noted in a region encoding the 19-kDa C-terminal epidermal growth factorlike domain of merozoite surface protein-1, a vaccine candidate. T he human malaria parasite Plasmodium vivax is prevalent worldwide, and accounts for 70-80 million cases annually, mostly in Asia and Latin America (1). Growing resistance of P. vivax strains to chloroquine is spurring the development of a vaccine against P. vivax malaria. One current vaccine candidate is merozoite surface protein-1 (MSP-1), a 200-kDa protein expressed on the surface of the P. vivax merozoite (2). MSP-1 of Plasmodium species is synthesized as a high-molecular-weight precursor and then processed into several fragments (3). At the time of red cell invasion by the merozoite, only the 19-kDa C-terminal fragment (MSP-1 19 ), which contains two epidermal growth factor-like domains, remains on the surface. Antibodies against MSP-1 19 inhibit merozoite entry into red cells (4), and immunization with MSP-1 19 protects monkeys from challenging infections (5, 6). Hence, MSP-1 19 is considered a promising vaccine candidate.Importantly, there is extensive allelic diversity of MSP-1 among isolates (7), and this polymorphism may hamper development of effective vaccines. In Plasmodium falciparum, the most virulent malaria parasite, polymorphism in PfMsp-1 is well characterized. PfMsp-1 consists of several interallele variable blocks flanked by conserved or semiconserved blocks. Variation in this gene is basically dimorphic; i.e., one or the other of two different residues (8, ...

BackgroundIn order to control malaria, it is important to understand the genetic structure of the parasites in each endemic area. Plasmodium vivax is widely distributed in the tropical to temperate regions of Asia and South America, but effective strategies for its elimination have yet to be designed. In South Korea, for example, indigenous vivax malaria was eliminated by the late 1970s, but re-emerged from 1993. We estimated the population structure and temporal dynamics of transmission of P. vivax in South Korea using microsatellite DNA markers.Methodology/Principal FindingsWe analyzed 255 South Korean P. vivax isolates collected from 1994 to 2008, based on 10 highly polymorphic microsatellite DNA loci of the P. vivax genome. Allelic data were obtained for the 87 isolates and their microsatellite haplotypes were determined based on a combination of allelic data of the loci. In total, 40 haplotypes were observed. There were two predominant haplotypes: H16 and H25. H16 was observed in 9 isolates (10%) from 1996 to 2005, and H25 in 27 (31%) from 1995 to 2003. These results suggested that the recombination rate of P. vivax in South Korea, a temperate country, was lower than in tropical areas where identical haplotypes were rarely seen in the following year. Next, we estimated the relationships among the 40 haplotypes by eBURST analysis. Two major groups were found: one composed of 36 isolates (41%) including H25; the other of 20 isolates (23%) including H16. Despite the low recombination rate, other new haplotypes that are genetically distinct from the 2 groups have also been observed since 1997 (H27).Conclusions/SignificanceThese results suggested a continual introduction of P. vivax from other population sources, probably North Korea. Molecular epidemiology using microsatellite DNA of the P. vivax population is effective for assessing the population structure and transmission dynamics of the parasites - information that can assist in the elimination of vivax malaria in endemic areas.

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The present study was designed to investigate polymorphism in Duffy binding protein (DBP) gene of Plasmodium vivax isolates of Korea. Thirty samples were obtained from P. vivax patients in Yonchon-gun, Kyonggi-do in 1998. The PCR products of the samples were subjected to sequencing and hybridization analyses of the regions II and IV of P. vivax DBP gene. Two genotypes, SK-1 and SK-2, were identified on the basis of amino acid substitution and deletion. The genotype of 10 isolates was SK-1 and that of 20 isolates was SK-2. Most of the predicted amino acids in the region II of DBP gene were conserved between the Korean isolates and Belem strain except for 4-5 amino acid substitutions. In the region IV of DBP, a 6-bp insert that was shown in the Sal-1 allele type was found in SK-1, and a 27-bp insert that was shown in the Papua New Guinea allele type was found in SK-2. In conclusion, the present findings suggest that two genotypes of P. vivax coexist in the endemic area of Korea.

Kocuria spp. are members of the Micrococcaceae family that are frequently found in the environment and on human skin. Few human infections have been reported. We describe what appear to be the first two cases of Kocuria marina peritonitis in patients undergoing continuous ambulatory peritoneal dialysis. CASE REPORTS Case 1.A 57-year-old man was admitted to the emergency department because of turbid dialysis effluent for 1 day. He had end-stage renal disease as a result of diabetic nephropathy and had been undergoing continuous ambulatory peritoneal dialysis (CAPD) for 6 years. Upon physical examination, he was afebrile, with a normal-appearing catheter exit site. However, the peritoneal dialysate fluid was straw colored and cloudy, with a total leukocyte count of 0.78 ϫ 10 9 leukocytes/ liter and a neutrophil count of 90%. No microorganisms were seen on a Gram stain. In the peripheral blood, the hemoglobin concentration was 10.1 g/dl, the white blood cell (WBC) count was 7.40 ϫ 10 9 cells/liter, and the platelet count was 171 ϫ 10 9 platelets/liter. The C-reactive protein concentration was 2.76 mg/dl (reference concentration, Ͻ0.5 mg/dl), and the serum urea and creatinine concentrations were 53 mg/dl and 11.2 mg/dl, respectively. Intraperitoneal administration of netilmicin and narrow-spectrum cephalosporin (ceftezole) was started for empirical treatment of CAPD peritonitis, which was changed to intraperitoneal ceftazidime and clindamycin when there was no response. Culture of the dialysate yielded a pure culture of grampositive cocci in pairs or clusters (strain M07-0128). After 48 h of incubation at 35°C in 5% CO 2 on sheep blood agar, the 1-to 2-mm colonies were nonhemolytic and yellow. The isolate was identified as Kocuria varians/Kocuria kristinae with a 50.28%/49.72% probability, respectively, by a Vitek 2 system (bioMérieux, St. Louis, MO) and as K. kristinae (code number 6714014) with a 99.3% probability by an API Staph system (bioMérieux, Marcy l'Etoile, France). We performed 16S rRNA gene sequencing as previously described (5) and compared the obtained sequence with sequences similar to those of the type strains using BLAST and EzTaxon (4). The result showed 99.86% homology with Kocuria marina; the second closest match was Kocuria carniphila, with 98.30% homology. This isolate was finally identified as K. marina by 16S rRNA gene sequence analysis. In spite of the start of administration of intravenous vancomycin on day 10, the response remained unsatisfactory. The Tenckhoff catheter in his abdomen was removed on day 17, and he was switched to hemodialysis with the placement of an arteriovenous shunt. The patient improved with antibiotic therapy for 7 days after catheter removal and was discharged.We performed antimicrobial susceptibility testing on the isolate using the agar dilution method, according to the Clinical and Laboratory Standards Institute (CLSI) guidelines for Staphylococcus (4a). The isolate was susceptible to penicillin, ampicillin, ampicillin-sulbactam, gentamicin, cephalothin (cefaloti...

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Apical membrane antigen-1 is a candidate vaccine component for malaria. In the present study, we investigated the polymorphism of the Plasmodium vivax apical membrane antigen-1 gene ( PvAMA-1) in 30 Korean isolates. The polymorphic region of the PvAMA-1 gene, corresponding to nucleotides 324-735 (aa 108-245), was amplified using polymerase chain reaction followed by cloning and sequencing. Two genotypes ( SKA and SKG) were identified on the basis of amino acid substitution. These were identical to those of the Chinese isolates. The Korean isolates showed sequence variation at six positions on the basis of the sequence of the Sal1 strain. Of these, variation at position 189 (Glu/Lys) was found only in SKA. These two genotypes were related to the genotype of the circumsporozoite and Duffy binding protein of the Korean isolate. These findings suggest that two genotypes of P. vivax coexist in the endemic area and that the re-emerging parasite in Korea may be related to or have originated in East Asia.