Genetic diversity and natural selection of Duffy binding protein of Plasmodium vivax Korean isolates

Plasmodium vivax Duffy binding protein (PvDBP) is a micronemal type I membrane protein that plays an essential role in erythrocyte invasion of merozoites. PvDBP is a prime blood stage vaccine candidate antigen against P. vivax, but its polymorphic nature represents a major obstacle to the successful design of a protective vaccine against vivax malaria. In this study, we analyzed the genetic polymorphism and natural selection at the N-terminal cysteine-rich region of PvDBP (PvDBPII) among 70 P. vivax isolates collected from Korean patients during 2005–2010. Seventeen single nucleotide polymorphisms (SNP), which resulted in 14 non-synonymous and 3 synonymous mutations, were found in PvDBPII among the Korean P. vivax isolates. Sequence analyses revealed that 13 different PvDBPII haplotypes, which were clustered into 3 distinct clades, were identified in Korean P. vivax isolates. The difference between the rates of nonsynomyous and synonymous mutations suggested that the region has evolved under natural selection. High selective pressure preferentially acted on regions identified or predicted to be B- and T-cell epitopes and MHC binding regions of PvDBPII. Recombination may also contribute to genetic diversity of PvDBPII. Our results suggest that PvDBPII of Korean P. vivax isolates display a limited genetic polymorphism and are under selective pressure. These results have significant implications for understanding the nature of the P. vivax population circulating in Korea and provide useful information for development of malaria vaccines based on this antigen.     

Antibody responses and avidity of naturally acquired anti-Plasmodium vivax Duffy binding protein (PvDBP) antibodies in individuals from an area with unstable malaria transmission

Plasmodium vivax remains an important cause of morbidity outside Africa, and no effective vaccine is available against this parasite. The P. vivax Duffy binding protein (PvDBP) is essential during merozoite invasion into erythrocytes, and it is a target for protective immunity against malaria. This investigation was designed to evaluate naturally acquired antibodies to two variant forms of PvDBP-II antigen (DBP-I and -VI) in malaria individuals (N = 85; median = 22 years) who were living in hypoendemic areas in Iran. The two PvDBP-II variants were expressed in Escherichia coli, and immunoglobulin G (IgG) isotype composition and avidity of naturally acquired antibodies to these antigens were measured using enzyme-linked immunosorbent assay (ELISA). Results showed that almost 32% of the studied individuals had positive antibody responses to the two PvDBP-II variants, and the prevalence of responders did not differ significantly (P > 0.05; χ(2) test). The IgG-positive samples exhibited 37.03% and 40.8% high-avidity antibodies for PvDBP-I and PvDBP-VI variants, respectively. Furthermore, high-avidity IgG1 antibody was found in 39.1% of positive sera for each examined variant antigen. The avidity of antibodies for both PvDBP variant antigens and the prevalence of responders with high- and intermediate-avidity IgG, IgG1, and IgG3 antibodies were similar in patients (P > 0.05; χ(2) test). Moreover, the prevalence of IgG antibody responses to the two variants significantly increased with exposure and host age. To sum up, the results provided additional data in our understanding of blood-stage immunity to PvDBP, supporting the rational development of an effective blood-stage vaccine based on this antigen.     

Dynamics of asymptomatic Plasmodium vivax infections and Duffy binding protein polymorphisms in relation to parasitemia levels in Papua New Guinean children

The interaction between Plasmodium vivax Duffy binding protein II (PvDBPII) and human erythrocyte Duffy antigen is necessary for blood stage infections. However, PvDBPII is highly polymorphic. We recently observed that certain recombinant DBPII variants bind better to erythrocytes in vitro. To examine the hypothesis that haplotypes with enhanced binding have increased parasitemia levels, we followed 206 Papua New Guinean children biweekly for six months with a total of 713 P. vivax samples genotyped. Twenty-seven PvDBPII haplotypes were identified, and 3 haplotypes accounted for 57% of the infections. The relative frequencies of dominant haplotypes remained stable throughout the study. There was no significant association with PvDBPII alleles or haplotypes with P. vivax parasitemia. The dominant haplotype (26% of samples), however, corresponded to a high-binding haplotype. Thus, common haplotypes are not likely to have arisen from increased fitness as measured by greater parasitemia levels. The restricted number of common haplotypes increases the feasibility of a PvDBPII-based vaccine.     

The risk of malarial infections and disease in Papua New Guinean children

In a treatment re-infection study of 206 Papua New Guinean school children, we examined risk of reinfection and symptomatic malaria caused by different Plasmodium species. Although children acquired a similar number of polymerase chain reaction-detectable Plasmodium falciparum and P. vivax infections in six months of active follow-up (P. falciparum = 5.00, P. vivax = 5.28), they were 21 times more likely to develop symptomatic P. falciparum malaria (1.17/year) than P. vivax malaria (0.06/year). Children greater than nine years of age had a reduced risk of acquiring P. vivax infections of low-to-moderate (>150/microL) density (adjusted hazard rate [AHR] = 0.65 and 0.42), whereas similar reductions in risk with age of P. falciparum infection was only seen for parasitemias > 5,000/microL (AHR = 0.49) and symptomatic episodes (AHR = 0.51). Infection and symptomatic episodes with P. malariae and P. ovale were rare. By nine years of age, children have thus acquired almost complete clinical immunity to P. vivax characterized by a very tight control of parasite density, whereas the acquisition of immunity to symptomatic P. falciparum malaria remained incomplete. These observations suggest that different mechanisms of immunity may be important for protection from these malaria species.     

中国中部地区间日疟原虫分离株Duffy血型结合蛋白Ⅱ区的克隆表达与初步鉴定

目的克隆中国中部地区间日疟原虫分离株Duffy血型结合蛋白Ⅱ区基因(PvDBPⅡ),体外表达和鉴定重组PvDBPⅡ蛋白。方法PCR法从间日疟患者血液DNA样品中扩增PvDBPⅡ基因,将产物插入到原核表达载体pET28a(+)中,构建pET28a PvDBPⅡ重组表达质粒,转化大肠埃希菌(E.coli)BL21(DE3+),异丙基βD硫代吡喃半乳糖苷诱导表达带有His标签的重组蛋白,采用镍柱亲和层析纯化重组蛋白,相应表达物分别采用十二烷基磺酸钠聚丙烯酰胺凝胶电泳和Western blot进行分析鉴定。结果PCR扩增的PvDBPII基因为1.1 kb,重组pET28a PvDBPⅡ质粒经测序验证,其插入片段序列与GenBank参考序列相似性为99%,转化E.coli所表达的重组蛋白分子量约为44 kDa,且能被间日疟患者血清特异性识别。结论成功克隆了PvDBPⅡ基因,表达了重组PvDBPII蛋白,为进一步研究基于PvDBPⅡ的红内期间日疟疫苗奠定了基础。     

Fy(a)/Fy(b) antigen polymorphism in human erythrocyte Duffy antigen affects susceptibility to Plasmodium vivax malaria

Plasmodium vivax (Pv) is a major cause of human malaria and is increasing in public health importance compared with falciparum malaria. Pv is unique among human malarias in that invasion of erythrocytes is almost solely dependent on the red cell's surface receptor, known as the Duffy blood-group antigen (Fy). Fy is an important minor blood-group antigen that has two immunologically distinct alleles, referred to as Fy(a) or Fy(b), resulting from a single-point mutation. This mutation occurs within the binding domain of the parasite's red cell invasion ligand. Whether this polymorphism affects susceptibility to clinical vivax malaria is unknown. Here we show that Fy(a), compared with Fy(b), significantly diminishes binding of Pv Duffy binding protein (PvDBP) at the erythrocyte surface, and is associated with a reduced risk of clinical Pv in humans. Erythrocytes expressing Fy(a) had 41-50% lower binding compared with Fy(b) cells and showed an increased ability of naturally occurring or artificially induced antibodies to block binding of PvDBP to their surface. Individuals with the Fy(a+b-) phenotype demonstrated a 30-80% reduced risk of clinical vivax, but not falciparum malaria in a prospective cohort study in the Brazilian Amazon. The Fy(a+b-) phenotype, predominant in Southeast Asian and many American populations, would confer a selective advantage against vivax malaria. Our results also suggest that efficacy of a PvDBP-based vaccine may differ among populations with different Fy phenotypes.     

The Duffy blood group and resistance to Plasmodium vivax in Honduras.

To test the hypothesis that the Duffy blood group negative genotype is a factor in resistance to Plasmodium vivax, we determined the Duffy blood group, the malaria antibodies, and the slide-demonstrated infection rates with P. vivax and P. falciparum of 420 persons living in Nueva Armenia, Honduras. In all, 247 persons were Duffy negative. Demonstrated infections with P. falciparum were almost equally distributed between Duffy-positive (5,8%) and Duffy-negative (4.9%) persons. Similarly, Duffy-positive (25.6%) and Duffy-negative (28.2%) persons had equal proportions of indirect fluorescent antibody test titers suggestive of past or present P. falciparum infection. In contrast, all 14 P. vivax infections were found in Duffy-negative persons. There was no evidence suggesting that Duffy-positive and Duffy-negative persons had different exposures to malaria. The Duffy negative genotype FyFy appears to be a factor in resistance to P. vivax.     

Anti-Plasmodium vivax duffy binding protein antibodies measure exposure to malaria in the Brazilian Amazon

Plasmodium vivax Duffy binding protein (DBP) is functionally important in the erythrocyte invasion process and provides a logical target for vaccine-mediated immunity. In the current study, we demonstrated that DBP is naturally immunogenic in different populations of the Brazilian Amazon, and the proportions of DBP IgG positive subjects increased with exposure to malaria, reaching a peak in those subjects with long-term exposure (> 15 years) in the Amazon area. This profile of antibody response was significantly different from the one observed for the P. vivax merozoite surface protein 1 (MSP1(19)), which was relatively uniform in areas with markedly different levels of malaria transmission. In a small sample of adults with symptomless P. vivax infection, we could not detect any significant correlation between antibodies against these P. vivax proteins and asymptomatic infection. Our study provided an additional insight by demonstrating cumulative exposure as a determinant that acts independently of host age in generation of anti-DBP IgG response.     

Emergence of FY*A(null) in a Plasmodium vivax-endemic region of Papua New Guinea

In Papua New Guinea (PNG), numerous blood group polymorphisms and hemoglobinopathies characterize the human population. Human genetic polymorphisms of this nature are common in malarious regions, and all four human malaria parasites are holoendemic below 1500 meters in PNG. At this elevation, a prominent condition characterizing Melanesians is alpha(+)-thalassemia. Interestingly, recent epidemiological surveys have demonstrated that alpha(+)-thalassemia is associated with increased susceptibility to uncomplicated malaria among young children. It is further proposed that alpha(+)-thalassemia may facilitate so-called "benign" Plasmodium vivax infection to act later in life as a "natural vaccine" against severe Plasmodium falciparum malaria. Here, in a P. vivax-endemic region of PNG where the resident Abelam-speaking population is characterized by a frequency of alpha(+)-thalassemia >/=0.98, we have discovered the mutation responsible for erythrocyte Duffy antigen-negativity (Fy[a-b-]) on the FY*A allele. In this study population there were 23 heterozygous and no homozygous individuals bearing this new allele (allele frequency, 23/1062 = 0.022). Flow cytometric analysis illustrated a 2-fold difference in erythroid-specific Fy-antigen expression between heterozygous (FY*A/FY*A(null)) and homozygous (FY*A/FY*A) individuals, suggesting a gene-dosage effect. In further comparisons, we observed a higher prevalence of P. vivax infection in FY*A/FY*A (83/508 = 0.163) compared with FY*A/FY*A(null) (2/23 = 0.087) individuals (odds ratio = 2.05, 95% confidence interval = 0.47-8.91). Emergence of FY*A(null) in this population suggests that P. vivax is involved in selection of this erythroid polymorphism. This mutation would ultimately compromise alpha(+)-thalassemia/P. vivax-mediated protection against severe P. falciparum malaria.     

Plasmodium vivax Duffy binding protein: baseline antibody responses and parasite polymorphisms in a well‐consolidated settlement of the Amazon Region

Objective  To investigate risk factors associated with the acquisition of antibodies against Plasmodium vivax Duffy binding protein (PvDBP) – a leading malaria vaccine candidate – in a well‐consolidated agricultural settlement of the Brazilian Amazon Region and to determine the sequence diversity of the PvDBP ligand domain (DBP_II) within the local malaria parasite population. Methods  Demographic, epidemiological and clinical data were collected from 541 volunteers using a structured questionnaire. Malaria parasites were detected by conventional microscopy and PCR, and blood collection was used for antibody assays and molecular characterisation of DBP_II. Results  The frequency of malaria infection was 7% (6% for P. vivax and 1% for P. falciparum), with malaria cases clustered near mosquito breeding sites. Nearly 50% of settlers had anti‐PvDBP IgG antibodies, as detected by enzyme‐linked immunosorbent assay (ELISA) with subject’s age being the only strong predictor of seropositivity to PvDBP. Unexpectedly, low levels of DBP_II diversity were found within the local malaria parasites, suggesting the existence of low gene flow between P. vivax populations, probably due to the relative isolation of the studied settlement. Conclusion  The recognition of PvDBP by a significant proportion of the community, associated with low levels of DBP_II diversity among local P. vivax, reinforces the variety of malaria transmission patterns in communities from frontier settlements. Such studies should provide baseline information for antimalarial vaccines now in development.     

Duffy blood group and malaria

Very important progress has been made over the last years in understanding the Duffy blood group system and its complexity. The Duffy blood group antigen serves not only as blood group antigen, but also as a receptor for a family of proinflammatory cytokines termed chemokines, and as a receptor for Plasmodium vivax malaria parasites. The Duffy antigen has been termed the "Duffy Antigen Receptor for Chemokines" (DARC) or the Duffy chemokine receptor. DARC might play a role as a scanvenger on the red blood cell surface to eliminate excess of toxic chemokines produced in some pathologic situations [48]. Plasmodium vivax (P. vivax) causes approximately between 70 and 80 million cases of malaria per year and is the most amply distributed human malaria in the world [51]. Individuals with the Duffy-negative phenotype are resistant to P. vivax invasion, and the molecular mechanism that gives rise to the phenotype Fy(a - b - ) in black individuals has been associated with a point mutation - 33TC expressed in homozigosity in the FYB allele [5]. Despite P. vivax be widespread throughout the tropical and subtropical world, it is absent from West Africa, where more than 95% of the population is Duffy negative. Recently, this point mutation has been described in heterozigosity in the FYA allele in others malaria endemic regions [7, 8], and until now we do not know if it confers a certain degree of protection against P. vivax infection.     

Duffy blood group and malaria

Very important progress has been made over the last years in understanding the Duffy blood group system and its complexity. The Duffy blood group antigen serves not only as blood group antigen, but also as a receptor for a family of proinflammatory cytokines termed chemokines, and as a receptor for Plasmodium vivax malaria parasites. The Duffy antigen has been termed the "Duffy Antigen Receptor for Chemokines" (DARC) or the Duffy chemokine receptor. DARC might playa role as a scanvenger on the red blood cell surface to eliminate excess of toxic chemokines produced in some pathologic situations [48].

Plasmodium vivax (P. vivax) causes approximately between 70 and 80 million cases of malaria per year and is the most amply distributed human malaria in the world [51]. Individuals with the Duffy-negative phenotype are resistant to P. vivax invasion, and the molecular mechanism that gives rise to the phenotype Fy(a – b – ) in black individuals has been associated with a point mutation ?33TC expressed in homozigosity in the FYB allele [5]. Despite P. vivax be widespread throughout the tropical and subtropical world, it is absent from West Africa, where more than 95% of the population is Duffy negative. Recently, this point mutation has been described in heterozigosity in the FYA allele in others malaria endemic regions [7, 8], and until now we do not know if it confers a certain degree of protection against P. vivax infection.     

Leucocyte migration inhibition test in human Plasmodium vivax malaria

Specific antigen-induced T-lymphocyte response in human P. vivax malaria has been studied by a leucocyte migration inhibition test. The test was performed in four groups: (1) American/European controls; (2) Indians with acute P. vivax malaria; (3) immune Indians with no clinical attacks of malaria for 5 years; and (4) Indians with chronic infection. Group 3 showed significantly high inhibition as compared to group 1 (P less than 0.001) and group 2 (P less than 0.01). There was however no significant difference between the 'immune' and 'chronic' groups. Indirect haemagglutinating antibodies were also monitored in the test sera and there was an inverse correlation (r = -0.613; P less than 0.01) between IHA antibodies in serum and percentage leucocyte migration inhibition.     

Relapse/reinfection patterns of Plasmodium vivax infection: a four year study.

In an endemic area relapse and reinfection in Plasmodium vivax cases poses serious problems for the malaria control program. We have studied the relapse/reinfection patterns of P. vivax infection in 26 villages of District Shahjahanpur, a malaria endemic area of UP, India for a period of four years (May, 1986 to October, 1988). All the P. vivax cases were given a complete course of radical treatment and were followed-up for relapse/reinfection. There were 8,914, 2,484, 1,439 and 883 P. vivax cases in 1986, 1987 and 1989 respectively, our of which 2,066, 141, 58 and 18 cases in the respective years showed relapse/reinfection. The maximum number of relapse/reinfection was recorded from a 47 year old male patient, who suffered from P. vivax infection eight times. The percentage occurrence of relapse/reinfection was much higher (70.2%) in males compared with females (29.8%). Relapses were more common among 16-30 years old patients. In conclusion it was felt that in 1986 relapse/reinfection in vivax cases was higher due to improper treatment of these cases. This situation may have occurred due to lack of awareness among the public, poor surveillance by the National Malaria Program or higher density of the vector mosquitos in the area.     

Lymphocyte subpopulations in malaria infected individuals living in an endemic area

Development of partial immunity in people living in malaria endemic area is complex. For better understanding, the lymphocyte subpopulations from infected patients were evaluated by flow cytometer before any antimalarial treatment. In P. vivax infection, the frequency of T-helper type 1 (Th1) was decreased significantly (p = 0.042). In contrast, the number of T- helper type 2 (Th2) was increased significantly (p = 0.001). These trends have also been observed in P. faciparum infection. The Th2 predominant response to the natural malaria infection is likely due to persistent stimulation by Plasmodium species. In P. falciparum infection, CD8+ cytotoxic lymphocytes were significantly reduced (p = 0.007). However, such changes were not found in P. vivax infection. This might suggest that CD8+ cell responses to different Plasmodium spp in a different way. Both Th2 activation and CD8+ cell suppression may reflect less protective effects and chronic malaria infection could be established.     

Real-time multiplex allele-specific polymerase chain reaction for genotyping of the Duffy antigen, the Plasmodium vivax invasion receptor

BACKGROUND AND OBJECTIVES: Duffy blood group is of major interest in clinical medicine as it is not only involved in blood-transfusion risks and occasionally in neonatal haemolytic disease, but it is also the receptor for the human malaria parasite Plasmodium vivax in the erythrocyte invasion. The aim of this study was to develop a rapid and inexpensive approach for high-throughput Duffy genotyping. MATERIALS AND METHODS: This paper reported the development of a Duffy genotyping assay based on multiplex real-time polymerase chain reaction (PCR) using SYBR Green I fluorescent dye. RESULTS: By using this approach for Duffy genotyping we obtained the same results as that for the conventional allele-specific PCR, however, in a high-throughput assay. The Duffy genotyping of field samples demonstrated that P. vivax-infected individuals showed a significantly higher prevalence of two functional alleles than Plasmodium falciparum-infected and non-infected individuals. This finding corroborates the hypothesis that the presence of two functional alleles increases the risk of P. vivax infection. CONCLUSION: This methodology may be suitable for epidemiological studies, particularly for exploring the relationship between Duffy alleles and malaria susceptibility, and also for identification of transfusional incompatibility in blood banks.     

Comparison of IgG reactivities to Plasmodium vivax merozoite invasion antigens in a Brazilian Amazon population

Naturally acquired antibody reactivity to two major Plasmodium vivax vaccine candidates was investigated in 294 donors from three malaria-endemic communities of Rond?nia state, Brazil. Antibody recognition of recombinantly expressed antigens covering five different regions of P. vivax reticulocyte binding protein 1 (PvRBP1) and region II of P. vivax Duffy binding protein (PvDBP-RII) were compared. Positive IgG responses to these antigens were significantly related to the level of malaria exposure in terms of past infections and years of residence in the endemic area when corrected for age. The highest prevalence of anti-PvRBP1 total IgG antibodies corresponded to the amino acid regions denoted PvRBP1(431-748) (41%) and PvRBP1(733-1407) (47%). Approximately one-fifth of positively responding sera had titers of at least 1:1,600. Total IgG responses to PvDBP-RII were more prevalent (67%), of greater magnitude, and acquired more rapidly than those to individual PvRBP1 antigens. Responses to both PvRBP1 and PvDBP-RII were biased toward the cytophilic subclasses IgG1 and IgG3. These data provide the first insights on acquired antibody responses to PvRBP1 and a comparative view with PvDBP-RII that may prove valuable for understanding protective immune responses to these two vaccine candidates as they are evaluated as components of multitarget blood-stage vaccines.     

Clinical features of children hospitalized with malaria--a study from Bikaner, northwest India

Severe Plasmodium vivax malaria in adults has been reported from Bikaner (northwestern India) but the reports on children are scanty. This prospective study was done on 303 admitted children of malaria. The diagnosis was done by peripheral blood smear and rapid diagnostic test. Further confirmation of severe P. vivax monoinfection was done by polymerase chain reaction (PCR). The proportion of P. falciparum, P. vivax, and mixed (P. falciparum and P. vivax) infection was 61.01%, 33.99%, and 4.95%, respectively. Severe disease was present in 49.5% (150/303) children with malaria, with the risk greatest among P. vivax monoinfection (63.1% [65/103]) compared with P. falciparum, either alone (42.7% [79/185]; odds ratio [OR] = 2.3 [95% confidence interval (CI) = 1.40-3.76], P = 0.001) or mixed infections (40% [6/15]; OR = 2.57 [95% CI = 0.88-7.48]). In children < 5 years of age, the proportion of severe malaria attributable to P. vivax rose to 67.4% (31/46) compared with 30.4% (14/46) of P. falciparum (OR = 4.7 [95% CI = 2.6-8.6], P < 0.0001) and 2.2% (1/46) of mixed infection (OR = 92 [95% CI = 24.6-339.9], P < 0.0001). The proportion of patients having severe manifestations, which included severe anemia, thrombocytopenia, cerebral malaria, acute respiratory distress syndrome, hepatic dysfunction, renal dysfunction, abnormal bleeding was significantly high in association with P. vivax monoinfection in 0-5 year age group, while the same was significantly high in association with P. falciparum monoinfection in 5-10 year age group. Similarly P. vivax monoinfection had greatest propensity to cause multiorgan dysfunction in 0-5 year age group (34.1% [17/41], P < 0.0001) in comparison to P. falciparum monoinfection, which had similar propensity in 5-10 year age group (36.8% [35/95], P = 0.039). Plasmodium vivax monoinfection was almost equally serious to cause significant mortality in comparison to P. falciparum (case fatality rate of severe P. vivax was 3.9% versus 3.2% of severe P. falciparum malaria; P = 1.0). This study reaffirms the evidence of severe P. vivax malaria in children in Bikaner.     

Immunization of Aotus monkeys with recombinant cysteine-rich interdomain region 1 alpha protects against severe disease during Plasmodium falciparum reinfection

BACKGROUND: After continuous exposure to malarial infections in regions of Africa where malaria is hyperendemic, children attain clinical immunity. This immunity results, in part, from the acquisition of antibodies against a large repertoire of variant antigens expressed on the surface of infected erythrocytes, such as the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1). We determined whether a subunit vaccine to a portion of PfEMP1 could induce protection in nonhuman primates. METHODS: We immunized Aotus nancymai monkeys with PfEMP1 recombinant (r) cysteine-rich interdomain region 1 alpha (CIDR1 alpha ) and infected them twice with P. falciparum Vietnam Oak Knoll strain, the most virulent strain of P. falciparum in Aotus monkeys--each infection expressed a different PfEMP1. Anti-PfEMP1 antibodies were analyzed by enzyme-linked immunosorbent assay against rCIDR1 alpha and by flow cytometry against infected erythrocytes. RESULTS: Immunization with rCIDR1 alpha was not protective, despite delayed patency during the first infection, but it protected monkeys against severe anemia during reinfection. Protection against anemia is associated with a more rapid increase in antibodies to PfEMP1. CONCLUSION: The findings of reduced severe disease in rCIDR1 alpha -vaccinated Aotus monkeys provide experimental support for a PfEMP1-based vaccine to protect African children against severe malarial disease. Such vaccination may function by priming for the accelerated acquisition of immunity to new PfEMP1 variants.     

Relapses of Plasmodium vivax infection usually result from activation of heterologous hypnozoites

BACKGROUND: Relapses originating from hypnozoites are characteristic of Plasmodium vivax infections. Thus, reappearance of parasitemia after treatment can result from relapse, recrudescence, or reinfection. It has been assumed that parasites causing relapse would be a subset of the parasites that caused the primary infection. METHODS: Paired samples were collected before initiation of antimalarial treatment and at recurrence of parasitemia from 149 patients with vivax malaria in Thailand (n=36), where reinfection could be excluded, and during field studies in Myanmar (n=75) and India (n=38). RESULTS: Combined genetic data from 2 genotyping approaches showed that novel P. vivax populations were present in the majority of patients with recurrent infection (107 [72%] of 149 patients overall [78% of patients in Thailand, 75% of patients in Myanmar {Burma}, and 63% of patients in India]). In 61% of the Thai and Burmese patients and in 55% of the Indian patients, the recurrent infections contained none of the parasite genotypes that caused the acute infection. CONCLUSIONS: The P. vivax populations emerging from hypnozoites commonly differ from the populations that caused the acute episode. Activation of heterologous hypnozoite populations is the most common cause of first relapse in patients with vivax malaria.