Plasmodium vivax circumsporozoite genotypes: a limited variation or new subspecies with major biological consequences?

<p>Abstract</p> <p>Background</p> <p><it>Plasmodium vivax </it>circumsporozoite variants have been identified in several geographical areas. The real implication of the genetic variation in this region of the <it>P. vivax </it>genome has been questioned for a long time. Although previous studies have observed significant association between VK210 and the Duffy blood group, we present here that evidences of this variation are limited to the CSP central portion.</p> <p>Methods</p> <p>The phylogenetic analyses were accomplished starting from the amplification of conserved domains of <it>18 SSU RNAr </it>and <it>Cyt B</it>. The antibodies responses against the CSP peptides, MSP-1, AMA-1 and DBP were detected by ELISA, in plasma samples of individuals infected with two <it>P. vivax CS </it>genotypes: VK210 and <it>P. vivax</it>-like.</p> <p>Results</p> <p>These analyses of the two markers demonstrate high similarity among the <it>P. vivax CS </it>genotypes and surprisingly showed diversity equal to zero between VK210 and <it>P. vivax</it>-like, positioning these <it>CS </it>genotypes in the same clade. A high frequency IgG antibody against the N- and C-terminal regions of the <it>P. vivax </it>CSP was found as compared to the immune response to the R- and V- repetitive regions (<it>p </it>= 0.0005, Fisher's Exact test). This difference was more pronounced when the <it>P. vivax</it>-like variant was present in the infection (<it>p </it>= 0.003, Fisher's Exact test). A high frequency of antibody response against MSP-1 and AMA-1 peptides was observed for all <it>P. vivax CS </it>genotypes in comparison to the same frequency for DBP.</p> <p>Conclusions</p> <p>This results target that the differences among the <it>P. vivax CS </it>variants are restrict to the central repeated region of the protein, mostly nucleotide variation with important serological consequences.</p

Duffy blood group gene polymorphisms among malaria vivax patients in four areas of the Brazilian Amazon region

<p>Abstract</p> <p>Background</p> <p>Duffy blood group polymorphisms are important in areas where <it>Plasmodium vivax </it>predominates, because this molecule acts as a receptor for this protozoan. In the present study, Duffy blood group genotyping in <it>P. vivax </it>malaria patients from four different Brazilian endemic areas is reported, exploring significant associations between blood group variants and susceptibility or resistance to malaria.</p> <p>Methods</p> <p>The <it>P. vivax </it>identification was determined by non-genotypic and genotypic screening tests. The Duffy blood group was genotyped by PCR/RFLP in 330 blood donors and 312 malaria patients from four Brazilian Amazon areas. In order to assess the variables significance and to obtain independence among the proportions, the Fisher's exact test was used.</p> <p>Results</p> <p>The data show a high frequency of the <it>FYA/FYB </it>genotype, followed by <it>FYB/FYB, FYA/FYA</it>, <it>FYA/FYB-33 </it>and <it>FYB/FYB-33</it>. Low frequencies were detected for the <it>FYA/FY</it>^<it>X</it>, <it>FYB/FY</it>^<it>X</it>, <it>FYX/FY</it>^{<it>X </it>}and <it>FYB-33/FYB-33 </it>genotypes. Negative Duffy genotype (<it>FYB-33/FYB-33</it>) was found in both groups: individuals infected and non-infected (blood donors). No individual carried the <it>FY</it>^<it>X</it><it>/FYB-33 </it>genotype. Some of the Duffy genotypes frequencies showed significant differences between donors and malaria patients.</p> <p>Conclusion</p> <p>The obtained data suggest that individuals with the <it>FYA/FYB </it>genotype have higher susceptibility to malaria. The presence of the <it>FYB-33 </it>allele may be a selective advantage in the population, reducing the rate of infection by <it>P. vivax </it>in this region. Additional efforts may contribute to better elucidate the physiopathologic differences in this parasite/host relationship in regions endemic for <it>P. vivax </it>malaria, in particular the Brazilian Amazon region.</p

Serological detection of <it>Plasmodium vivax </it>malaria using recombinant proteins corresponding to the 19-kDa C-terminal region of the merozoite surface protein-1

Abstract Background Serological tests to detect antibodies specific to Plasmodium vivax could be a valuable tool for epidemiological studies, for screening blood donors in areas where the malaria is not endemic and for diagnosis of infected individuals. Because P. vivax cannot be easily obtained in vitro, ELISA assays using total or semi-purified antigens are rarely used. Based on this limitation, we tested whether recombinant proteins representing the 19 kDa C-terminal region of the merozoite surface protein-1 of P. vivax (MSP119) could be useful for serological detection of malaria infection. Methods Three purified recombinant proteins produced in Escherichia coli (GST-MSP119, His6-MSP119 and His6-MSP119-PADRE) and one in Pichia pastoris (yMSP119-PADRE) were compared for their ability to bind to IgG antibodies of individuals with patent P. vivax infection. The method was tested with 200 serum samples collected from individuals living in the north of Brazil in areas endemic for malaria, 53 serum samples from individuals exposed to Plasmodium falciparum infection and 177 serum samples from individuals never exposed to malaria. Results Overall, the sensitivity of the ELISA assessed with sera from naturally infected individuals was 95%. The proportion of serum samples that reacted with recombinant proteins GST-MSP119, His6-MSP119, His6-MSP119-PADRE and yMSP119-PADRE was 90%, 93.5%, 93.5% and 93.5%, respectively. The specificity values of the ELISA determined with sera from healthy individuals and from individuals with other infectious diseases were 98.3% (GST-MSP119), 97.7% (His6-MSP119 and His6-MSP119-PADRE) or 100% (yMSP119-PADRE). Conclusions Our study demonstrated that for the Brazilian population, an ELISA using a recombinant protein of the MSP119 can be used as the basis for the development of a valuable serological assay for the detection of P. vivax malaria.</p

Genetic structure of Plasmodium falciparum populations in the Brazilian Amazon region.

After a major increase in incidence between the 1970s and the 1990s, the Brazilian Amazon region now accounts for the most cases of Plasmodium falciparum malaria in the Americas. Polymorphism of 10 microsatellite loci in the P. falciparum genome was studied in 196 isolates obtained from 5 populations in the region. There was significant multilocus linkage disequilibrium, particularly within populations with lower proportions of mixed-genotype infections. However, most multilocus genotypes in different isolates were distinct, and there was no evidence of any recent epidemic expansion of particular clones. Genetic divergence between populations was very substantial but did not fit a simple model of isolation by distance. Thus, different foci of P. falciparum in Brazil are quite independent, with distinct population structures and minimal gene flow, a finding that has implications for strategies to control infection and to contain the spread of drug resistance at a regional level

Susceptibility of Anopheles aquasalis and An. darlingi to Plasmodium vivax VK210 and VK247

The susceptibility of Anopheles aquasalis (F3 generation) and An. darlingi (F1 generation) to Plasmodium vivax circumsporozoite protein phenotypes from a limited number of blood samples of malaria patients in Belém, state of Pará, Brazil, was examined. A polymerase chain reaction was used to determine the P. vivax phenotypes in blood samples and the blood-fed infected mosquitoes were dissected and tested by ELISA. In all patient infections, more infected An. aquasalis and An. darlingi were positive for VK210 compared with VK247