Long-lasting humoral and cellular immune responses elicited by immunization with recombinant chimeras of the Plasmodium vivax circumsporozoite protein

The circumsporozoite protein (CSP), the most abundant surface antigen of sporozoites, has been extensively studied in different expression platforms as a vaccine candidate. Clinical trials have shown the necessity of broad and highly avid humoral immune responses together with high numbers of CSP-specific T_CD4+ and T_CD8+ cells, especially those producing IFN-γ, to induce protection. To this aim, we designed two distinct recombinant immunogens based on previously-described antigenic fragments of Plasmodium vivax CSP (PvCSP) to be used as vaccine candidates. The first one is a virus-like particle (VLP) comprising the repeat region of PvCSP (B and T_CD4+ epitopes) within the loop of the hepatitis B virus core antigen (HBcAgPvCSP). The second one is a PvCSP multi-epitope polypeptide, rPvCSP-ME, designed based on antigenic regions of PvCSP recognized by lymphocytes of individuals from endemic areas.     

Concurrent dengue and malaria due to Plasmodium falciparum and P. vivax

Concurrent infections of dengue and malaria are rare. We report a case of dengue fever with acute malaria due to Plasmodium falciparum and P. vivax in which the presence of mixed infection with P. vivax was overlooked and confirmed later on during recurrence of the fever that had initially responded to conventional antimalarial treatment and symptomatic treatment for dengue fever. We suggest that in concurrent infections of dengue and malaria, possibility of mixed infection with various Plasmodium species should be excluded to ensure a better treatment outcome.     

Acute respiratory distress syndrome in Plasmodium vivax malaria: case report and review of the literature

Plasmodium vivax infection can cause acute respiratory distress syndrome (ARDS). This complication of P. vivax infection is being increasingly recognised and was life threatening in a traveller returning from Gujarat, India. Nineteen other published cases of P. vivax with respiratory symptoms are also reviewed and confirm that ARDS was the underlying complication in most cases. Plasmodium vivax-associated ARDS is a clinically recognisable condition whose underlying pathophysiology is likely to reflect processes that are independent of parasite sequestration in the pulmonary microvasculature.     

Risk of Plasmodium vivax malaria reintroduction in Uzbekistan: genetic characterization of parasites and status of potential malaria vectors in the Surkhandarya region

Plasmodium vivax malaria was eradicated from Uzbekistan in 1961. Due to resurgence of the disease in neighbouring states and massive population migration, there has been an increase of P. vivax malaria, imported from Tajikistan, resulting in a number of indigenous cases being identified in areas bordering that country. A molecular study using the merozoite surface protein 1 (msp-1) gene as a marker was performed on 24 P. vivax genomic isolates from 12 indigenous and 10 imported malaria cases that occurred in the Surkhandarya region during the summer of 2002. Results have shown a significant difference in the frequency of msp-1 types between indigenous and imported isolates, the latter showing greater genetic heterogeneity. An entomological investigation in the area suggested that three Anopheles species, namely A. superpictus, A. pulcherrimus and A. hyrcanus may have a potential role in the endemic transmission of P. vivax.     

Increasing incidence of malaria in the Negro River basin, Brazilian Amazon

Malaria in Brazil is virtually restricted to the Amazon Region, where it has a heterogeneous geographic distribution. We reviewed secondary data in order to describe the regional and temporal distribution of 8018 malaria cases seen between 2003 and 2007 in Santa Isabel do Rio Negro, a municipality in the northwest Brazilian Amazon. A significant rise in malaria incidence, mainly in the Yanomami Indian reservation, was observed during this time. Anopheline breeding sites were also mapped and entomological data were obtained through the capture of larval and adult mosquitoes. Thirty-three potential breeding sites were identified in the urban and periurban areas, 28 of which were positive for anopheline larvae. Anopheles darlingi specimens were captured in both intra- and peridomicile locations in the urban areas. Demographic data were also assessed via a sectional survey, revealing that the majority of dwellings were vulnerable to mosquitoes. This study suggests that urban and periurban areas of this municipality are highly susceptible to epidemic malaria, which is endemic in the Yanomami Indian reservation near the city. In addition, transmission can be perpetuated autochthonously in the urban area, drawing attention to the continuous need for preventative measures such as controlling adult and aquatic stages of mosquitoes and improving housing.     

Fatal Case of Plasmodium vivax Malaria in a Splenectomized Patient

Malaria is a major problem in tropical and sub-tropical countries, with high morbidity and mortality. Splenectomy makes patients more susceptible to serious bacterial and parasitic infections. We report for the first time in Iran a fatal case of Plasmodium vivax malaria, confirmed by microscopic and molecular (Semi-nested multiplex PCR) tests in a patient who had undergone splenectomy due to hemolytic anemia.     

Genetic diversity of T-helper cell epitopic regions of circumsporozoite protein of Plasmodium falciparum isolates from India

Genetic variation in the T-helper cell epitopic regions (Th2R and Th3R) of circumsporozoite protein of 135 Plasmodium falciparum isolates collected from different epidemic and endemic regions of India was studied. Variation in the Th2R and Th3R regions was found to exhibit restricted polymorphism and can be grouped. The variations were not regionally biased, as different isolates collected from different regions were found to belong to the same group. The Th2R and Th3R sequences were found to be linked in each isolate. Since the variations are regionally unbiased and restricted, the prototype variant from the groups could be included in a subunit polyvalent vaccine against sporozoites.     

In vivo Susceptibility of Plasmodium vivax to Chloroquine in Southeastern Iran

Background

Plasmodium vivax is the predominant species causes of malaria with about 90% total annual reported malaria in Iran. This study conducted to determine the susceptibility of Plasmodium vivax isolates to chloroquine in Sistan and Balochistan Province, southeastern Iran.

Methods

A total 270 subjects with symptomatic malaria and confirmed P. vivax infection completed the designed 28-day in vivo study. The thick and thin film blood smears were screened for malaria parasites by microscopy. The nested PCR was applied using the Plasmodium 18 subunit ribosomal ribonucleic (Ssr RNA) genes for detecting mixed infections and diagnosis of parasites in the samples with low parasite on days 0, 5, 6, 7, and 28.

Results

P. vivax was cleared in 15%, 50%, 95%, and 100% of patients on days 1, 2, 3, 4 respectively by microscopy assessment. Six patients were exhibited specific P. vivax band in nested PCR on day 5. No recurrence was observed on days 7, 14 and 28. Mean (±standard deviation) parasite clearance time was 2.41 (±0.8) days.

Conclusion

P. vivax is still susceptible to chloroquine in Southeatern Iran. This finding is compatible with results of neighboring countries Pakistan and Afghanistan.     

Plasmodium vivax infection among Duffy antigen-negative individuals from the Brazilian Amazon region: an exception?

We present evidence for Plasmodium vivax infection among Duffy blood group-negative inhabitants of Brazil. The P. vivax identification was determined by both genotypic and non-genotypic screening tests. The Duffy blood group was genotyped by PCR/RFLP and phenotyped using a microtyping kit. We detected two homozygous FY*B-33 carriers infected by P. vivax, whose circumsporozoite protein genotypes were VK210 and/or P. vivax-like. Additional efforts are necessary in order to clarify the evidence that P. vivax is being transmitted among Duffy blood group-negative patients from the Brazilian Amazon region.     

Retinal haemorrhage in vivax malaria

Retinal haemorrhage is often observed in patients with Plasmodium falciparum, especially when combined with cerebral malaria. However, few cases of retinopathy have been reported in P. vivax malaria. Benign tertian malaria has re-emerged among soldiers in the South Korean demilitarized zone since 1993. We report an indigenous case of retinal haemorrhage caused by P. vivax and review the relevant literature.     

Estimates of short- and long-term incubation periods of Plasmodium vivax malaria in the Republic of Korea

With the current epidemic of vivax malaria closely associated with the demilitarised zone along the border between North and South Korea, it has been suggested that the incubation period tends, in part, to be prolonged. Based on the detailed travel history of cases from 2000 to 2003 who reside in non-malarious areas, statistical estimates of the incubation periods were obtained. The data suggest that cases fall into two categories with short- and long-term incubation periods, respectively. Of 416 cases with available information, 72 and 79 successfully met our criteria for inferring the durations of short- and long-term incubation periods. The mean short- and long-term incubation periods were estimated to be 26.6 days (95% CI 21.0-32.2) and 48.2 weeks (95% CI 46.8-49.5), respectively. The maximum likelihood method was used to fit gamma and normal distributions to the short- and long-term incubation periods, assisting prediction of the frequency distribution of the overall incubation period, which exhibited a bimodal pattern. We postulate that the observed distribution reflects adaptation of the parasite to the seasonal population dynamics of the vector, Anopheles sinensis, ensuring continued transmission of vivax malaria in this temperate zone.     

Therapeutic response of multidrug-resistant Plasmodium falciparum and P. vivax to chloroquine and sulfadoxine-pyrimethamine in southern Papua, Indonesia

To determine the level of antimalarial drug resistance in southern Papua, Indonesia, we assessed the therapeutic efficacy of chloroquine plus sulfadoxine-pyrimethamine (CQ+SP) for Plasmodium falciparum infections as well as CQ monotherapy for P. vivax infections. Patients with P. falciparum failing therapy were re-treated with unsupervised quinine+/-doxycycline therapy and those with P. vivax with either unsupervised quinine+/-doxycycline or amodiaquine. In total, 143 patients were enrolled in the study (103 treated with CQ+SP and 40 with CQ). Early treatment failures occurred in four patients (4%) with P. falciparum and six patients (15%) with P. vivax. The failure rate by Day 28 for P. vivax was 65% (95% CI 49-81). After PCR correction for re-infections, the Day 42 recrudescence rate for P. falciparum infections was 48% (95% CI 31-65). Re-treatment with unsupervised quinine+/-doxycycline resulted in further recurrence of malaria in 48% (95% CI 31-65) of P. falciparum infections and 70% (95% CI 37-100) of P. vivax infections. Eleven patients with recurrent P. vivax were re-treated with amodiaquine; there were no early or late treatment failures. In southern Papua, a high prevalence of drug resistance of P. falciparum and P. vivax exists both to first- and second-line therapies. Preliminary data indicate that amodiaquine retains superior efficacy compared with CQ for CQ-resistant P. vivax.     

Sulfadoxine-pyrimethamine plus artesunate compared with chloroquine for the treatment of vivax malaria in areas co-endemic for Plasmodium falciparum and P. vivax: a randomised non-inferiority trial in eastern Afghanistan

Chloroquine (CQ) is an effective treatment of choice for vivax malaria in most settings, but with the spread of CQ-resistant Plasmodium falciparum, many countries now use artemisinin-based combination therapy for treatment of falciparum malaria. In areas co-endemic for falciparum and vivax malaria incorrect differential diagnosis is always a risk. In Afghanistan the adoption of sulfadoxine-pyrimethamine plus artesunate (SP+AS) as first-line falciparum treatment raises the prospect of a significant proportion of vivax malaria being misdiagnosed and treated with the combination. SP is considered to have limited efficacy against vivax malaria, and the efficacy of SP+AS against Plasmodium vivax has not been established in areas that are using SP+AS. A randomised, non-inferiority trial comparing SP+AS with CQ monotherapy was undertaken on 190 vivax malaria patients in eastern Afghanistan. Standard WHO procedures for in vivo evaluation of antimalarial drugs were followed. A total of 180 individuals completed the trial to day 42. Using a per protocol analysis, both regimens resulted in > or =96% treatment success at 28 d, but significantly more cases failed in the CQ arm (46%) than in the SP+AS arm (24%) by day 42. In areas where vivax infections might be misdiagnosed as falciparum infections and treated with SP+AS, patient management would be as good, or better than, with the standard CQ treatment.     

A qPCR-based multiplex assay for the detection of Wuchereria bancrofti, Plasmodium falciparum and Plasmodium vivax DNA

The purpose of this study was to develop real-time multiplex quantitative PCR (qPCR) assays for the simultaneous detection of Wuchereria bancrofti (Wb), Plasmodium falciparum (Pf) and P. vivax (Pv) in mosquitoes. We optimized the assays with purified DNA samples and then used these assays to test DNA samples isolated from Anopheles punctulatus mosquitoes collected in villages in Papua New Guinea where these infections are co-endemic. Singleplex assays detected Wb, Pf and Pv DNA in 32%, 19% and 15% of the mosquito pools, respectively, either alone or together with other parasites. Multiplex assay results agreed with singleplex results in most cases. Overall parasite DNA rates in mosquitoes, estimated by PoolScreen 2 software, for Wb, Pf and Pv were 4.9%, 2.7% and 2.1%, respectively. Parasite DNA rates were consistently higher in blood-fed mosquitoes than in host-seeking mosquitoes. Our results show that multiplex qPCR can be used to detect and estimate prevalence rates for multiple parasite species in arthropod vectors. We believe that multiplex molecular xenodiagnosis has great potential as a tool for non-invasively assessing the distribution and prevalence of vector-borne pathogens such as W. bancrofti and Plasmodium spp. in human populations and for assessing the impact of interventions aimed at controlling or eliminating these diseases.     

Plasmodium vivax gametocyte protein Pvs230 is a transmission-blocking vaccine candidate

The malaria transmission-blocking vaccine (TBV) aims to interfere the development of malaria parasite in the mosquito and prevent further transmission in the community. So far only two TBV candidates have been identified in Plasmodium vivax; ookinete surface proteins Pvs25 and Pvs28. The pvs230 (PVX_003905) is reported as an ortholog of Pfs230, a gametocyte/gamete stage TBV candidate in Plasmodium falciparum, however its candidacy for TBV has never been tested. Therefore here, we have investigated whether Pvs230 can be a TBV candidate using P. vivax samples obtained from Thailand. The mouse antiserum raised against the plasmid expressing CRDs I-IV of Pvs230 detected Pvs230 protein in the lysate of P. vivax gametocyte in western blot analysis under non-reducing condition. From the localization of Pvs230 on the outer most regions of gametocyte in the immunofluorescence assay, it appears that Pvs230 is localized on the surface of gametes. Importantly, the anti-Pvs230 mouse serum significantly reduced the number of P. vivax oocysts developed in the mosquito midgut. Moreover, the polymorphism in Pvs230 CRDs I-IV is limited suggesting that it may not be an impediment for the utilization of Pvs230 as an effective TBV candidate. In conclusion, our results show that Pvs230 is a transmission-blocking vaccine candidate of P. vivax.     

Therapeutic efficacy of chloroquine in Plasmodium vivax from areas with different epidemiological patterns in India and their Pvdhfr gene mutation pattern

Among the four human malaria parasites, drug resistance occurs mainly in Plasmodium falciparum. However, there are some reports of chloroquine (CQ) resistance in P. vivax from different geographical regions. In India, approximately 50% of a total of 2 million cases of malaria reported annually are due to P. vivax. CQ is the drug of choice for treatment. Since few cases of treatment failure have been reported from India, this study was undertaken to generate data systematically on the efficacy of CQ in 287 patients from different epidemiological regions. Cure rates for 28 days were 100% and there was a rapid parasite clearance rate in all age groups from all study sites. Although P. vivax has been reported to be inherently resistant to sulfonamide and pyrimethamine, Indian isolates exhibited only double mutations in dhfr in vitro.     

Absence of nucleotide polymorphism in a Plasmodium vivax multidrug resistance gene after failure of mefloquine prophylaxis in French Guyana

Vivax malaria is widespread and resistance has been described for chloroquine and sulfadoxine-pyrimethamine. We report on evidence of failure of mefloquine prophylaxis in a French soldier who contracted Plasmodium vivax in French Guyana, South America. Despite regular weekly mefloquine prophylaxis (250 mg/d), the patient presented with a first episode of vivax malaria, which was treated by chloroquine alone, then experienced a second crisis in France. The reappearance of the parasites occurred one day after the end of prophylaxis, confirming parasitological and clinical resistance in a non-immune patient. Mefloquine was detected by a liquid chromatography assay in plasma at a level of 1062 ng/ml, which was higher than the expected concentration after five months of weekly prophylaxis. This isolate had no single nucleotide polymorphisms of the pvmdr1 gene at seven allele positions: pvmdr1 N91, Y189, Y976, S1071, F1076, N1079 and D1291, corresponding to codons 86, 184, 939, 1034, 1039, 1042 and 1246 in P. falciparum. This observation of failure of mefloquine prophylaxis against P. vivax, when added to previously reported chloroquine and atovaquone-proguanil failure, strengthens the case for re-evaluating drug policies for vivax malaria and the need for continuous research on molecular markers of drug resistance.     

Haematinic treatment of anaemia increases the risk of Plasmodium vivax malaria in pregnancy

Nutritional deficiency and malaria are 2 major causes of anaemia during pregnancy in tropical areas. The relationship between anaemia, its treatment with iron and folate, and malaria was studied in a prospective cohort of 2112 pregnant Karen women on the north-western border of Thailand between 1993 and 1997. The development of Plasmodium vivax malaria was associated with a past mean haematocrit > 30% (hazard ratio = 1.5, 95% CI 1.2-2, P = 0.001) and recent (< or = 30 d) iron and folate supplementation (hazard ratio = 1.7, 95% CI 1.1-2.6, P = 0.01). There were no associations with P. falciparum infections. Plasmodium vivax has a predilection for young erythrocytes, and these results suggest that pregnant women with larger numbers of circulating young red cells are at greater risk of developing P. vivax malaria. In P. vivax-endemic areas, systematic iron and folate supplementation confers both benefit and risk in pregnancy.     

Worldwide sequence conservation of transmission-blocking vaccine candidate Pvs230 in Plasmodium vivax

Pfs230, surface protein of gametocyte/gamete of the human malaria parasite, Plasmodium falciparum, is a prime candidate of malaria transmission-blocking vaccine. Plasmodium vivax has an ortholog of Pfs230 (Pvs230), however, there has been no study in any aspects on Pvs230 to date. To investigate whether Pvs230 can be a vivax malaria transmission-blocking vaccine, we performed evolutionary and population genetic analysis of the Pvs230 gene (pvs230: PVX_003905). Our analysis of Pvs230 and its orthologs in eight Plasmodium species revealed two distinctive parts: an interspecies variable part (IVP) containing species-specific oligopeptide repeats at the N-terminus and a 7.5 kb interspecies conserved part (ICP) containing 14 cysteine-rich domains. Pvs230 was closely related to its orthologs, Pks230 and Pcys230, in monkey malaria parasites. Analysis of 113 pvs230 sequences obtained from worldwide, showed that nucleotide diversity is remarkably low in the non-repeat 8-kb region of pvs230 (θπ = 0.00118) with 77 polymorphic nucleotide sites, 40 of which results in amino acid replacements. A signature of purifying selection but not of balancing selection was seen on pvs230. Functional and/or structural constraints may limit the level of polymorphism in pvs230. The observed limited polymorphism in pvs230 should ground for utilization of Pvs230 as an effective transmission-blocking vaccine.