Naturally acquired antibodies to Plasmodium vivax blood-stage vaccine candidates (PvMSP-1₁₉ and PvMSP-3α₃₅₉₋₇₉₈ and their relationship with hematological features in malaria patients from the Brazilian Amazon

An important step when designing a vaccine is identifying the antigens that function as targets of naturally acquired antibodies. We investigated specific antibody responses against two Plasmodium vivax vaccine candidates, PvMSP-1₁₉ and PvMSP-3α_359?798. Moreover, we assessed the relationship between these antibodies and morbidity parameters. PvMSP-1₁₉ was the most immunogenic antigen and the frequency of responders to this protein tended to increase in P. vivax patients with higher parasitemia. For both antigens, IgG antibody responses tended to be lower in patients who had experienced their first bout of malaria. Furthermore, anemic patients presented higher IgG antibody responses to PvMSP-3α_359?798. Since the humoral response involves a number of antibodies acting simultaneously on different targets, we performed a Principal Component Analysis (PCA). Anemic patients had, on average, higher first principal component scores (IgG1/IgG2/IgG3/IgG4 anti-MSP3α), which were negatively correlated with hemoglobin levels. Since antibodies against PfMSP-3 have been strongly associated with clinical protection, we cannot exclude the possibility of a dual role of PvMSP-3 specific antibodies in both immunity and pathogenesis of vivax malaria. Our results confirm the high immunogenicity of the conserved C terminus of PvMSP-1 and points to the considerable immunogenicity of polymorphic PvMSP-3α_359?798 during natural infection.     

Molecular Evolution of PvMSP3α Block II in Plasmodium vivax from Diverse Geographic Origins

Block II of Plasmodium vivax merozoite surface protein 3α (PvMSP3α) is conserved and has been proposed as a potential candidate for a malaria vaccine. The present study aimed to compare sequence diversity in PvMSP3a block II at a local microgeographic scale in a village as well as from larger geographic regions (countries and worldwide). Blood samples were collected from asymptomatic carriers of P. vivax in a village at the western border of Thailand and PvMSP3α was amplified and sequenced. For population genetic analysis, 237 PvMSP3α block II sequences from eleven P. vivax endemic countries were analyzed. PvMSP3α sequences from 20 village-level samples revealed two length variant types with one type containing a large deletion in block I. In contrast, block II was relatively conserved; especially, some non-synonymous mutations were extensively shared among 11 parasite populations. However, the majority of the low-frequency synonymous variations were population specific. The conserved pattern of nucleotide diversity in block II sequences was probably due to functional/structural constraints, which were further supported by the tests of neutrality. Notably, a small region in block II that encodes a predicted B cell epitope was highly polymorphic and showed signs of balancing selection, signifying that this region might be influenced by the immune selection and may serve as a starting point for designing multi-antigen/stage epitope based vaccines against this parasite.     

Analysis of the Plasmodium vivax dihydrofolate reductase–thymidylate synthase gene sequence

A basis for the intrinsic resistance of some Plasmodium vivax isolates to pyrimethamine is suggested following the isolation of the bifunctional gene encoding dihydrofolate reductase–thymidylate synthase (DHFR-TS) of this human malaria parasite. Malaria parasites are dependent on this enzyme for folate biosynthesis. Specific inhibition of the DHFR domain of the enzyme by pyrimethamine blocks pyrimidine biosynthesis, leading to an inhibition of DNA replication. The gene was isolated by the polymerase chain reaction (PCR) from genomic DNA using degenerate oligonucleotides designed to hybridize on the highly conserved regions of the sequence. The nucleotide sequence was completed by screening P. vivax genomic bank. Sequence analysis revealed an open reading frame (ORF) of 1872 nucleotides encoding a deduced protein of 623 amino acids (aa). Alignment with other malarial DHFR-TS genes showed that a 237-residue DHFR domain and a 286-residue TS domain were separated by a 100-aa linker region. Comparison with other malarial species showed low and essentially no isology in the DHFR and junctional domains, respectively, whereas an extensive isology was observed in the TS domain. The characteristic features of the P. vivax DHFR-TS gene sequence include an insertion of a short repetitive tandem array within the DHFR domain that is absent in another human malaria parasite, P. falciparum, and a GC-biased aa composition, giving rise to highly GC-rich DHFR (50.8%), junctional (58.7%), and TS (40.5%) domains, as compared with other malaria parasites. Analysis of the 5′ noncoding region revealed the presence of a putative TATA box at 116 nucleotides upstream of the ATG start codon as well as a putative GC box at −636. Comparison of the DHFR sequences from pyrimethamine-sensitive and pyrimethamine-resistant P. vivax isolates revealed two residue changes: Ser « Arg-58 and Ser « Asn-117. These aa residues correspond to codons 59 and 108 in the P. falciparum DHFR active site in which similar aa substitutions (Cys « Arg-59 and Ser « Asn-108) are associated with pyrimethamine resistance. These findings may explain the intrinsic resistance of some P. vivax isolates to pyrimethamine.     

Modelling the Incidence of Plasmodium vivax and Plasmodium falciparum Malaria in Afghanistan 2006–2009

Background

Identifying areas that support high malaria risks and where populations lack access to health care is central to reducing the burden in Afghanistan. This study investigated the incidence of Plasmodium vivax and Plasmodium falciparum using routine data to help focus malaria interventions.

Methods

To estimate incidence, the study modelled utilisation of the public health sector using fever treatment data from the 2012 national Malaria Indicator Survey. A probabilistic measure of attendance was applied to population density metrics to define the proportion of the population within catchment of a public health facility. Malaria data were used in a Bayesian spatio-temporal conditional-autoregressive model with ecological or environmental covariates, to examine the spatial and temporal variation of incidence.

Findings

From the analysis of healthcare utilisation, over 80% of the population was within 2 hours’ travel of the nearest public health facility, while 64.4% were within 30 minutes’ travel. The mean incidence of P. vivax in 2009 was 5.4 (95% Crl 3.2–9.2) cases per 1000 population compared to 1.2 (95% Crl 0.4–2.9) cases per 1000 population for P. falciparum. P. vivax peaked in August while P. falciparum peaked in November. 32% of the estimated 30.5 million people lived in regions where annual incidence was at least 1 case per 1,000 population of P. vivax; 23.7% of the population lived in areas where annual P. falciparum case incidence was at least 1 per 1000.

Conclusion

This study showed how routine data can be combined with household survey data to model malaria incidence. The incidence of both P. vivax and P. falciparum in Afghanistan remain low but the co-distribution of both parasites and the lag in their peak season provides challenges to malaria control in Afghanistan. Future improved case definition to determine levels of imported risks may be useful for the elimination ambitions in Afghanistan.     

Asymptomatic infection with Plasmodium falciparum and Plasmodium vivax in the Brazilian Amazon Basin: to treat or not to treat?

In this study, we determined whether the treatment of asymptomatic parasites carriers (APCs), which are frequently found in the riverside localities of the Brazilian Amazon that are highly endemic for malaria, would decrease the local malaria incidence by decreasing the overall pool of parasites available to infect mosquitoes. In one village, the treatment of the 19 Plasmodium falciparum-infected APCs identified among the 270 residents led to a clear reduction (Z = -2.39, p = 0.017) in the incidence of clinical cases, suggesting that treatment of APCs is useful for controlling falciparum malaria. For vivax malaria, 120 APCs were identified among the 716 residents living in five villages. Comparing the monthly incidence of vivax malaria in two villages where the APCs were treated with the incidence in two villages where APCs were not treated yielded contradictory results and no clear differences in the incidence were observed (Z = -0.09, p = 0.933). Interestingly, a follow-up study showed that the frequency of clinical relapse in both the treated and untreated APCs was similar to the frequency seen in patients treated for primary clinical infections, thus indicating that vivax clinical immunity in the population is not species specific but only strain specific.     

Diversity in the circumsporozoite protein of Plasmodium vivax: Does it matter?

Since the gene encoding the malarial circumsporozoite surface protein was characterized a decade ago, the corresponding protein has been considered an important vaccine candidate. Victoria Mann, Michael Good and Allan Saul here discuss molecular variation in the circumsporozoite surface protein of Plasmodium vivax in this context. There is still doubt about the degree and importance of polymorphisms in non-repetitive regions of the molecule. The degree of polymorphisms and data on naturally occurring protective responses suggests there has been minimal immunological pressure; the authors contend that antigenic diversity is unlikely to be a major factor in the use of this antigen as a vaccine for P. vivax.     

Phytosociological survey in Brazilian forest genetic reserve of Caçador

A phytosociological survey was carried out in the Forest Genetic Reserve of Caçador, which belongs to the Brazilian Agriculture Research Corporation – EMBRAPA. The Genetic Reserve comprises an area of 1120 ha and has been managed by the Agricultural Research and Extension Corporation of the State of Santa Catarina (EPAGRI). A restricted random sampling by plots, with units of 2500 m² (100 x 25 m) was used, allocating 40 plots to stands containing Araucaria angustifolia. All trees with diameter 20 cm at breast height were measured. Frequency, density, dominance, soil coverage, and importance value were evaluated, The most important species indicated by these parameters were Araucaria angustifolia, Ocotea porosa, Cupania vernalis, Matayba eleagnoides, Mollinedia elegans, Ocotea pulchella, Ilex paraguariensis and Prunus brasiliensis. In spite of the very high mean basal area (35.84 m² ha^-1), mean density (222 trees ha^-1) and mean volume outside bark (531.14 m³ ha^-1) for A. angustifolia it was found that understory had low commercial value and a very low natural regeneration rate in the priority species for in situ conservation: A. angustifolia, Cedrela fissilis, I. paraguariensis, Mimosa scabrella, P. brasiliensis and O. porosa. Simpson's index has shown in this case a low floristic diversity of species however, as was expected, the highest levels of abundance, dominance and frequency were found for Araucaria angustifolia.     

Functional genetic variation in the Rev-Erbα pathway and lithium response in the treatment of bipolar disorder

Bipolar disorder (BD) is characterized by disruptions in circadian rhythms such as sleep and daily activity that often normalize after lithium treatment in responsive patients. As lithium is known to interact with the circadian clock, we hypothesized that variation in circadian 'clock genes' would be associated with lithium response in BD. We determined genotype for 16 variants in seven circadian clock genes and conducted a candidate gene association study of these in 282 Caucasian patients with BD who were previously treated with lithium. We found that a variant in the promoter of NR1D1 encoding Rev-Erbα (rs2071427) and a second variant in CRY1 (rs8192440) were nominally associated with good treatment response. Previous studies have shown that lithium regulates Rev-Erbα protein stability by inhibiting glycogen synthase kinase 3β (GSK3β). We found that GSK3β genotype was also suggestive of a lithium response association, but not statistically significant. However, when GSK3β and NR1D1 genotypes were considered together, they predicted lithium response robustly and additively in proportion to the number of response-associated alleles. Using lymphoblastoid cell lines from patients with BD, we found that both the NR1D1 and GSK3β variants are associated with functional differences in gene expression. Our findings support a role for Rev-Erbα in the therapeutic mechanism of lithium and suggest that the interaction between Rev-Erbα and GSK3β may warrant further study.     

Residue-Specific Analysis of Frustration in the Folding Landscape of Repeat β/α Protein Apoflavodoxin

Flavodoxin adopts the common repeat β/α topology and folds in a complex kinetic reaction with intermediates. To better understand this reaction, we analyzed a set of Desulfovibrio desulfuricans apoflavodoxin variants with point mutations in most secondary structure elements by in vitro and in silico methods. By equilibrium unfolding experiments, we first revealed how different secondary structure elements contribute to overall protein resistance to heat and urea. Next, using stopped-flow mixing coupled with far-UV circular dichroism, we probed how individual residues affect the amount of structure formed in the experimentally detected burst-phase intermediate. Together with in silico folding route analysis of the same point-mutated variants and computation of growth in nucleation size during early folding, computer simulations suggested the presence of two competing folding nuclei at opposite sides of the central β-strand 3 (i.e., at β-strands 1 and 4), which cause early topological frustration (i.e., misfolding) in the folding landscape. Particularly, the extent of heterogeneity in folding nuclei growth correlates with the in vitro burst-phase circular dichroism amplitude. In addition, ?-value analysis (in vitro and in silico) of the overall folding barrier to apoflavodoxin's native state revealed that native-like interactions in most of the β-strands must form in transition state. Our study reveals that an imbalanced competition between the two sides of apoflavodoxin's central β-sheet directs initial misfolding, while proper alignment on both sides of β-strand 3 is necessary for productive folding.     

Two genetic stocks of Steindachneridion melanodermatum living in sympatry in nature and genetic variability of wild parents and F₁ generation

Steindachneridion melanodermatum is a large Brazilian catfish, highly prized for sport fishing and for its meat. Specimens of this species, both caught in nature from Iguacu River and F(1) fish born in captivity, were analyzed with regard to patterns of RAPD molecular markers. Genetic similarity ranged from 0.57 to 0.95; two groups were determined for the wild specimens. The results suggest different genetic lineages in sympatry in nature. Heterozygosity and percentage of polymorphic loci were 0.31 and 79% and 0.23 and 62%, respectively, for the two populations of wild specimens and 0.26 and 66%, respectively, for those born in captivity.     

Changing the epidemiology of carbapenem-resistant Pseudomonas aeruginosa in a Brazilian teaching hospital: the replacement of São Paulo metallo-β-lactamase-producing isolates

In Brazil, carbapenem-resistant Pseudomonas aeruginosa isolates are closely related to the S?o Paulo metallo-β-lactamase (SPM) Brazilian clone. In this study, imipenem-resistant isolates were divided in two sets, 2002/2003 and 2008/2009, analysed by pulsed field gel electrophoresis and tested for the Ambler class B metallo-β-lactamase (MBL) genes blaSPM-1, blaIMP and blaVIM. The results show a prevalence of one clone related to the SPM Brazilian clone in 2002/2003. In 2008/2009, P. aeruginosa isolates were mostly MBL negative, genetically diverse and unrelated to those that had been detected earlier. These findings suggest that the resistance to carbapenems by these recent P. aeruginosa isolates was not due to the spread of MBL-positive SPM-related clones, as often observed in Brazilian hospitals.     

A Spatiotemporal Analysis of Brazilian Science from the Perspective of Researchers’ Career Trajectories

The growth of Brazilian scientific production in recent years is remarkable, which motivates an investigation on the factors, inside and outside the country, that helped shape this wealthy research environment. This article provides a thorough analysis of the education of researchers that constitute the main Brazilian research groups, using data on about 6,000 researchers involved in the country’s National Institutes of Science and Technology (INCT) initiative. Data on the steps taken by each researcher in her education, from the bachelor’s degree to doctorate, including a possible postdoctoral experience, and employment, are extracted from an official curriculum vitae repository. The location and the time at which each career step occurred define spatiotemporal career trajectories. We then analyze such trajectories considering additional data, including the area of knowledge of the INCTs to which each researcher is associated. We found an increasing prevalence of Brazilian institutions in the education of Brazilian scientists, as the number of doctorates earned abroad is decreasing over time. Postdoctoral stages, on the other hand, often take place in Europe or in the United States. Taking an international postdoctoral position after a full education in Brazil suggests a drive towards seeking higher-level exchange and cooperation with foreign groups in a more advanced career stage. Results also show that Brazilian researchers tend to seek employment in regions that are close to the institutions at which they received their bachelor’s degrees, suggesting low mobility within the country. This study can be instrumental in defining public policies for correcting distortions, and can help other developing countries that aim to improve their national science systems.