Cerebrospinal Fluid Immunoglobulins as Potential Biomarkers of Chikungunya Encephalitis.

Chikungunya virus causes fever and severe polyarthritis or arthralgia and is associated with neurologic manifestations that are sometimes challenging to diagnose. We demonstrate intrathecal synthesis of chikungunya antibodies in a patient with a history of acute infection complicated by encephalitis. The specificity of the intracerebral immune response supports early chikungunya-associated encephalitis diagnosis.

Genetic and structural analysis of polyomavirus BK T-antigens reveal a higher density of mutations at inter-domain and hexamerization regions, regardless the status of infection.

Polyomavirus BK (BKPyV) T-antigens (large and small tumor antigens, or Lt-ag and st-ag, respectively), control key aspects of viral replication and are able to regulate cell cycle, promoting cell proliferation. However, the structural effects of genetic mutations on T-antigens are poorly investigated. In this study, 214 sequences of T-antigens from individuals with different BKPyV infections (16 renal transplant with nephropathy; 78 asymptomatic renal transplant; 24 hematopoietic stem cell transplant with hemorrhagic cystitis; 96 healthy non-transplant), were analyzed from the genetic and structural standpoints. We found a high concentration of non-synonymous mutations at inter-domains and hexamerization regions of both proteins, being five of them under positive selection in the Lt-ag but none in the st-ag. The in silico analysis indicated that two mutations, located at positions 164 in the st-ag and 592 in the Lt-ag, would significantly affect the interaction with PP2A and p53 cell targets, respectively, although they were not associated to a specific clinical status. No mutations were detected on the J-domains or at the ATPase motif. In sum, the profile of the mutations found seem not to be associated to increased morbidity. This is the first work to analyze structural modifications on T-antigens in different BKPyV infections, and managed to map conserved and variable regions of the T-antigens, which will be helpful for the study of new antiviral drugs.

Simian malaria in the Brazilian Atlantic forest: first description of natural infection of capuchin monkeys (Cebinae subfamily) by Plasmodium simium.

BACKGROUND: In Brazil, two species of Plasmodium have been described infecting non-human primates, Plasmodium brasilianum and Plasmodium simium. These species are morphologically, genetically and immunologically indistinguishable from the human Plasmodium malariae and Plasmodium vivax parasites, respectively. Plasmodium simium has been observed naturally infecting monkeys of the genera Alouatta and Brachyteles in a restricted area of the Atlantic Forest in the south and southeast regions of Brazil. However, its reported geographical distribution and the diversity of its vertebrate hosts may be underestimated, since available data were largely based on analyses by microscopic examination of peripheral blood, a method with limited sensitivity, considering the potential sub-patent feature of these infections. The present study describes, for the first time, the natural infection of P. simium in capuchin monkeys from the Brazilian Atlantic Forest. METHODS: Blood samples from 30 non-human primates belonging to nine species kept in the Primate Centre of Rio de Janeiro were collected. Fragments of spleen and liver from one dead monkey found in the neighborhoods of the Primate Centre were also analysed. Molecular diagnosis was performed by nested PCR (18SSU rRNA) and the amplified fragment was sequenced. RESULTS: Thirty per cent of the captive animals were infected with P. simium and/or P. brasilianum. The dead monkey tested positive for DNA of P. simium. For the first time, Cebinae primates (two specimens of genus Cebus and two of genus Sapajos) were found naturally infected by P. simium. The infection was confirmed by sequencing a small fragment of 18SSU rRNA. CONCLUSION: The results highlight the possibility of infection by P. simium in other species of non-human primates whose impact could be significant for the malaria epidemiology among non-human primates and, if it becomes clear that this P. simium is able to infect monkeys and, eventually, man, also for the maintenance of transmission of human malaria in the context of a zoonosis in areas under influence of the Atlantic Forest.

Genetic diversity of chloroquine-resistant Plasmodium vivax parasites from the western Brazilian Amazon.

The molecular basis of Plasmodium vivax chloroquine (CQ) resistance is still unknown. Elucidating the molecular background of parasites that are sensitive or resistant to CQ will help to identify and monitor the spread of resistance. By genotyping a panel of molecular markers, we demonstrate a similar genetic variability between in vitro CQ-resistant and sensitive phenotypes of P. vivax parasites. However, our studies identified two loci (MS8 and MSP1-B10) that could be used to discriminate between both CQ-susceptible phenotypes among P. vivax isolates in vitro. These preliminary data suggest that microsatellites may be used to identify and to monitor the spread of P. vivax-resistance around the world.

In vitro-reduced susceptibility to artemether in P. falciparum and its association with polymorphisms on transporter genes.

Plasmodium falciparum with reduced sensitivity to artemisinin derivatives has been observed in endemic areas, but the molecular mechanisms for this reduced sensitivity remain unclear. We evaluated the association between in vitro susceptibility of P. falciparum isolates obtained from southwest Nigeria and polymorphisms in selected putative transporter genes (PFE0775C, PF13_0271, pfmrp1, pfcrt, and pfmdr1). Modified schizont inhibition assay was used to determine the in vitro parasite susceptibility to artemether (ATH). Polymorphisms in selected genes were detected by polymerase chain reaction followed by direct DNA sequencing. The half-maximal inhibitory concentration (IC(50)) geometric mean (GM) for all P. falciparum isolates was 1.78 nM (range, 0.03-10.43 nM). Polymorphisms at codons 241, 86, and 76 of PFE0775C, pfmdr1, and pfcrt genes, respectively, were associated with reduced susceptibility to ATH. A new S263P single-nucleotide polymorphism on the PFE0775C gene was also detected in 27% of the isolates. Patient isolates harboring V241L or S263P polymorphisms on the PFE0775C gene showed increased IC(50) (GM: 3.08 nM and 1.79 nM, respectively). Plasmodium falciparum isolates harboring mutant Y86 pfmdr1 and P263 PFE0775C alleles showed a 2.5-5.5-fold increase in ATH IC(50.) This study shows that polymorphisms on the PFE0775C and pfmdr1 genes are associated with reduced sensitivity to ATH in fresh isolates of P. falciparum from Nigeria.

Pfatp6 molecular profile of Plasmodium falciparum isolates in the western Brazilian Amazon.

BACKGROUND: Anti-malarial drug resistance has emerged as one of the biggest challenges confronting the worldwide effort to control malaria. The appearance of chloroquine and multi-drug resistance had devastating effects on therapeutic efficacy of former first-line agents. Artemisinin has proven to be an excellent therapeutic alternative to fill the void in chemotherapeutic options left by resistance mechanisms. At the time of introduction, no resistance to artemisinins had been recorded, and artemisinins demonstrated excellent parasite reduction rates. In an attempt to protect artemisinin efficacy, the World Health Organization (WHO) made artemisinin-based combination therapy (ACT) its official first-line treatment recommendation for uncomplicated Plasmodium falciparum in 2006. In Brazil, artemether/lumefantrine became the Brazilian Malaria Control Programme's official treatment recommendation in 2007. The sarco/endoplasmic reticulum Ca2+ - ATPase ortholog of P. falciparum (pfatp6) has been suggested as one of the targets of artemisinins. Consequently, pfatp6 gene polymorphisms are being investigated as markers of artemisinin resistance elsewhere. The goal of this work was to describe the molecular profile of pfatp6 in P. falciparum isolates from different localities in the Amazonas State. METHODS: DNA polymorphisms of the pfatp6 gene in 80 P. falciparum isolates from 11 municipalities of the Amazonas State (Western Brazilian Amazon), before and after the introduction of ACT in the Brazilian anti-malarial guidelines, were analysed by automatic sequencing. Mutations in the pfatp6 gene were searched using Mutation Surveyor v3.25 software. RESULTS: The P. falciparum pfatp6 gene presented polymorphisms at codons 37, 630 and 898. The R37K mutation was found in 16% of the samples, A630S in 32% and I898I in 52%. No S769N mutation, however, was detected in the analysed samples. CONCLUSION: Despite the small number of samples, data presented here provide baseline information about polymorphisms of pfatp6 gene before and after exposure to ACT in a low transmission area, which will help to infer drug selection pressure in this area in the future.

Chloroquine and sulphadoxine-pyrimethamine sensitivity of Plasmodium falciparum parasites in a Brazilian endemic area.

BACKGROUND: The goal of the present study was the characterization of Plasmodium falciparum genes associated to malaria drug resistance (pfcrt, pfdhfr and pfdhps), in samples from two Brazilian localities. METHODS: Parasites from 65 P. falciparum samples were genotyped using nested-PCR and direct DNA sequencing. RESULTS: Six resistant sulphadoxine-pyrimethamine (SP) pfdhfr genotypes and one haplotype associated to SP sensitivity were detected. For pfcrt gene, SVMNT chloroquine (CQ)-resistant genotype was detected as well as the CVMNK CQ-sensitive haplotype in the same sample from Paragominas, that showed a SP-sensitive genotype. CONCLUSION: This study is the first to document the sensitivity of P. falciparum parasites to CQ and SP in Brazilian field samples. The importance of these findings is discussed.

Evaluation of the genetic polymorphism of Plasmodium falciparum P126 protein (SERA or SERP) and its influence on naturally acquired specific antibody responses in malaria-infected individuals living in the Brazilian Amazon.

BACKGROUND: The Plasmodium falciparum P126 protein is an asexual blood-stage malaria vaccine candidate antigen. Antibodies against P126 are able to inhibit parasite growth in vitro, and a major parasite-inhibitory epitope has been recently mapped to its 47 kDa N-terminal extremity (octamer repeat domain--OR domain). The OR domain basically consists of six octamer units, but variation in the sequence and number of repeat units may appear in different alleles. The aim of the present study was to investigate the polymorphism of P126 N-terminal region OR domain in P. falciparum isolates from two Brazilian malaria endemic areas and its impact on anti-OR naturally acquired antibodies. METHODS: The study was carried out in two villages, Candeias do Jamari (Rondonia state) and Peixoto de Azevedo (Mato Grosso state), both located in the south-western part of the Amazon region. The repetitive region of the gene encoding the P126 antigen was PCR amplified and sequenced with the di-deoxy chain termination procedure. The antibody response was evaluated by ELISA with the Nt47 synthetic peptide corresponding to the P126 OR-II domain. RESULTS: Only two types of OR fragments were identified in the studied areas, one of 175 bp (OR-I) and other of 199 bp (OR-II). A predominance of the OR-II fragment was observed in Candeias do Jamari whereas in Peixoto de Azevedo both fragments OR-I and OR-II were frequent as well as mixed infection (both fragments simultaneously) reported here for the first time. Comparing the DNA sequencing of OR-I and OR-II fragments, there was a high conservation among predicted amino acid sequences of the P126 N-terminal extremity. Data of immune response demonstrated that the OR domain is highly immunogenic in natural conditions of exposure and that the polymorphism of the OR domain does not apparently influence the specific immune response. CONCLUSION: These findings confirm a limited genetic polymorphism of the P126 OR domain in P. falciparum isolates and that this limited genetic polymorphism does not seem to influence the development of a specific humoral immune response to P126 and its immunogenicity in the studied population.

BK polyomavirus genotypes Ia and Ib1 exhibit different biological properties in renal transplant recipients.

BK polyomavirus (BKV) is an opportunist agent associated with nephropathy (BKVAN) in 1-10% of kidney transplant recipients. BKV is classified into genotypes or subgroups according to minor nucleotidic variations with unknown biological implications. Studies assessing the possible association between genotypes and the risk of BKVAN in kidney transplant patients have presented conflicting results. In these studies, genotype Ia, which is highly prevalent in Brazil, was less frequently found and, thus, comparative data on the biological properties of this genotype are lacking. In this study, BKV Ia and Ib1 genotypes were compared according to their viral load, genetic evolution (VP1 and NCCR) - in a cohort of renal transplant recipients. The patients infected with Ia (13/23; 56.5%) genotype exhibited higher viral loads in urine [>1.4 log over Ib1 (10/23; 43.5%); p=0.025]. In addition, genotype Ia was associated with diverse mutations at VP1 loops and sites under positive selection outside loops, which were totally absent in Ib1. Although the number of viremic patients was similar, the three patients who had BK nephropathy (BKVAN) were infected with Ia genotype. NCCR architecture (ww or rr) were not distinctive between Ia and Ib1 genotypes. Ia genotype, which is rare in other published BKV cohorts, presented some diverse biological properties in transplanted recipients in comparison to Ib1.

Phylogenetic and structural analysis of merkel cell polyomavirus VP1 in Brazilian samples.

Our understanding of the phylogenetic and structural characteristics of the Merkel Cell Polyomavirus (MCPyV) is increasing but still scarce, especially in samples originating from South America. In order to investigate the properties of MCPyV circulating in the continent in more detail, MCPyV Viral Protein 1 (VP1) sequences from five basal cell carcinoma (BCC) and four saliva samples from Brazilian individuals were evaluated from the phylogenetic and structural standpoint, along with all complete MCPyV VP1 sequences available at Genbank database so far. The VP1 phylogenetic analysis confirmed the previously reported pattern of geographic distribution of MCPyV genotypes and the complexity of the South-American clade. The nine Brazilian samples were equally distributed in the South-American (3 saliva samples); North American/European (2 BCC and 1 saliva sample); and in the African clades (3 BCC). The classification of mutations according to the functional regions of VP1 protein revealed a differentiated pattern for South-American sequences, with higher number of mutations on the neutralizing epitope loops and lower on the region of C-terminus, responsible for capsid formation, when compared to other continents. In conclusion, the phylogenetic analysis showed that the distribution of Brazilian VP1 sequences agrees with the ethnic composition of the country, indicating that VP1 can be successfully used for MCPyV phylogenetic studies. Finally, the structural analysis suggests that some mutations could have impact on the protein folding, membrane binding or antibody escape, and therefore they should be further studied.

Polymorphisms in cg2 and pfcrt genes and resistance to chloroquine and other antimalarials in vitro in Plasmodium falciparum isolates from Colombia.

Polymorphisms in Plasmodium falciparum cg2 and pfcrt genes and their association with chloroquine resistance in vitro in Colombian parasites were evaluated in this study. Association of chloroquine resistance with resistance to other antimalarial drugs in vitro was also examined. Polymerase chain reactions (PCR) for kappa and omega cg2 regions and nested PCR and digestion with ApoI enzyme for K-76T pfcrt point mutation defined corresponding polymorphisms in 83 samples collected between 1995 and 1999. The isotopic microtest was used to evaluate sensitivity in vitro in a subgroup of 18 isolates. The predominant cg2 pattern observed was 13K/14omega repeats (46/83 [55.4%]) and all samples presented the K-76T mutant allele. Seventy-eight percent of samples were resistant to chloroquine in vitro, 35.3% to amodiaquine, 16.7% to mefloquine, and 5.6% to quinine. Significant correlations (P < 0.05) were observed between the IC50s of chloroquine and arteether, and among IC50s of arteether, mefloquine, and quinine. These results suggest the development of multiple and cross-resistance of Colombian P. falciparum isolates to second- and third-line antimalarials and new alternative drugs.

Different patterns of pfcrt and pfmdr1 polymorphisms in P. falciparum isolates from Nigeria and Brazil: the potential role of antimalarial drug selection pressure.

The effect of antimalarial drug selection on pfcrt and pfmdr1 polymorphisms in Plasmodium falciparum isolates from two distinct geographical locations was determined in 70 and 18 P. falciparum isolates from Nigeria and Brazil, respectively, using nested polymerase chain reaction and direct DNA sequencing approaches. All isolates from Brazil and 72% from Nigeria harbored the mutant SVMNT and CVIET pfcrt haplotype, respectively. The pfcrt CVMNT haplotype was also observed in (7%) of the Nigerian samples. One hundred percent (100%) and 54% of the parasites from Brazil and Nigeria, respectively, harbored wild-type pfmdr1Asn86. We provide first evidence of emergence of the CVMNT haplotype in West Africa. The high prevalence of pfcrt CVIET and SVMNT haplotypes in Nigeria and Brazil, respectively, is indicative of different selective pressure by chloroquine and amodiaquine. Continuous monitoring of pfcrt SVMNT haplotype is required in endemic areas of Africa, where artesunate-amodiaquine combination is used for treatment of acute uncomplicated malaria.

Population genetics of GYPB and association study between GYPB*S/s polymorphism and susceptibility to P. falciparum infection in the Brazilian Amazon.

BACKGROUND: Merozoites of Plasmodium falciparum invade through several pathways using different RBC receptors. Field isolates appear to use a greater variability of these receptors than laboratory isolates. Brazilian field isolates were shown to mostly utilize glycophorin A-independent invasion pathways via glycophorin B (GPB) and/or other receptors. The Brazilian population exhibits extensive polymorphism in blood group antigens, however, no studies have been done to relate the prevalence of the antigens that function as receptors for P. falciparum and the ability of the parasite to invade. Our study aimed to establish whether variation in the GYPB*S/s alleles influences susceptibility to infection with P. falciparum in the admixed population of Brazil. METHODS: Two groups of Brazilian Amazonians from Porto Velho were studied: P. falciparum infected individuals (cases); and uninfected individuals who were born and/or have lived in the same endemic region for over ten years, were exposed to infection but have not had malaria over the study period (controls). The GPB Ss phenotype and GYPB*S/s alleles were determined by standard methods. Sixty two Ancestry Informative Markers were genotyped on each individual to estimate admixture and control its potential effect on the association between frequency of GYPB*S and malaria infection. RESULTS: GYPB*S is associated with host susceptibility to infection with P. falciparum; GYPB*S/GYPB*S and GYPB*S/GYPB*s were significantly more prevalent in the in the P. falciparum infected individuals than in the controls (69.87% vs. 49.75%; P<0.02). Moreover, population genetics tests applied on the GYPB exon sequencing data suggest that natural selection shaped the observed pattern of nucleotide diversity. CONCLUSION: Epidemiological and evolutionary approaches suggest an important role for the GPB receptor in RBC invasion by P. falciparum in Brazilian Amazons. Moreover, an increased susceptibility to infection by this parasite is associated with the GPB S+ variant in this population.

Differential evolution of Human Immunodeficiency Virus type 1 Protease and Reverse Transcriptase genes between HAART-failing and naïve-treated individuals.

We described differential selective pressures along codon sites of the RT and PR genes of HIV-1 from HAART-failing and naïve-treated individuals, through the comparison of the ratio of non-synonymous mutations (d(N)) to synonymous mutations (d(S)) substitution per site. Resistance-associated mutations were found in 1/71 (1.4%) and 109/117 (93.1%) samples from naïve-treated and HAART-failing individuals, respectively, although most of positively selected codons represented polymorphisms in positions 123, 211, 245, 297 in RT and 37, 63 in PR of naïve-treated samples and positions 122, 123, 245, 272, 277, 286, 297 in RT and 10, 15, 20, 35, 37, 62, 63, 64, 71, 72, 77, 93 in PR of HAART-failing samples, except by ARV-resistance codons 74, 184, 215 in RT and 90 in PR exclusively found in HAART-failing group. The number and diversity of sites under selective pressure at populational level also increased in RT but not in PR of treated individuals. Our results demonstrated no evolution of drug-associated codons among untreated individuals, indicating unlikely transmission and adaptation of resistant HIV-1 strains in a free drug environment. Polymorphic sites observed exclusively in HAART-failing group, may contribute to HIV-1 escape and adaptation at individual and populational levels in a drug environment, although those mutually found in HIV-1 despite of previous exposure to ARV treatment, should not be considered accurate resistance markers.

Genetic diversity of chloroquine-resistant Plasmodium vivax parasites from the western Brazilian Amazon

The molecular basis of Plasmodium vivax chloroquine (CQ) resistance is still unknown. Elucidating the molecular background of parasites that are sensitive or resistant to CQ will help to identify and monitor the spread of resistance. By genotyping a panel of molecular markers, we demonstrate a similar genetic variability between in vitro CQ-resistant and sensitive phenotypes of P. vivax parasites. However, our studies identified two loci (MS8 and MSP1-B10) that could be used to discriminate between both CQ-susceptible phenotypes among P. vivax isolates in vitro. These preliminary data suggest that microsatellites may be used to identify and to monitor the spread of P. vivax-resistance around the world.

Differential antibody responses to Plasmodium falciparum invasion ligand proteins in individuals living in malaria-endemic areas in Brazil and Cameroon.

Antibody responses to malaria invasion ligands and proteins on the merozoite surface have been shown to interfere with red cell invasion and correlate with immunity to malaria. The current study is the first to characterize the antibody responses to EBA-140 and EBA-181, Plasmodium falciparum invasion ligands implicated in the alternative pathways of invasion, in age-matched populations of individuals living in endemic areas in both Brazil and Cameroon. Antibody responses to the proteins screened were different between populations. The African individuals reacted strongly with most fragments of these two EBAs, while the majority of the individuals from Mato Grosso, Brazil, reacted weakly and those from the Amazon had elevated responses to these EBA proteins. When compared with the responses against MSP-1(19) and EBA-175, it appeared that the Brazilian population has a variable ability to recognize P. falciparum invasion ligand proteins and that these responses are distinct from the African population.

Antimalarial activity of phenazines from lapachol, beta-lapachone and its derivatives against Plasmodium falciparum in vitro and Plasmodium berghei in vivo.

The antimalarial activity of benzo[a]phenazines synthesized from 1,2-naphthoquinone, lapachol, beta-lapachone and several derivatives have been tested against Plasmodium falciparum in vitro using isolates of parasites with various susceptibilities to chloroquine and/or mefloquine. Parasite growth in the presence of the test drugs was measured by incorporation of [(3)H]-hipoxanthine in comparison to controls with no drugs, always testing in parallel chloroquine, a standard antimalarial. Among seven benzophenazines tested, four had significant in vitro activities; important, the parasites resistant to chloroquine were more susceptible to the active phenazines in vitro. The doses of phenazines causing 50% inhibition of parasite growth varied from 1.67 to 9.44 microM. The two most active ones were also tested in vivo against Plasmodium berghei in mice, in parallel with lapachol and beta-lapachone. The 3-sulfonic acid-beta-lapachone-derived phenazine was the most active causing up to 98% inhibition of parasitaemia in long term treatment (7 doses) subcutaneously, whereas the phenazine from 3-bromo-beta-lapachone was inactive. Thus, these simple phenazines, containing polar (-Br,-I) and ionizable (-SO(3)H, -OH) groups, easily synthesized from cheap, natural or synthetic precursors (lapachol and beta-lapachone), at rather low cost, provide prototypes for development of new antimalarials aiming the chloroquine resistant parasites.

Antimalarial activity of Bidens pilosa L. (Asteraceae) ethanol extracts from wild plants collected in various localities or plants cultivated in humus soil.

Bidens pilosa (Asteraceae), a medicinal plant used worldwide, has antimalarial activity as shown in previous work. This study tested ethanol extracts from wild plants collected in three different regions of Brazil and from plants cultivated in various soil conditions. The extracts were active in mice infected with P. berghei: doses of < or =500 mg/kg administered by oral route reduced malaria parasitaemia and mouse mortality; higher doses were found to be less effective. Tested in vitro against three P. falciparum isolates, two chloroquine resistant and one mefloquine resistant, the plants cultivated under standard conditions, and in humus enriched soil, were active; but the wild plants were the most active. Analysis using thin layer chromatography demonstrated the presence of flavonoids (compounds considered responsible for the antimalarial activity) in all plants tested, even though at different profiles. Because B. pilosa is proven to be active against P. falciparum drug-resistant parasites in vitro, and in rodent malaria in vivo, it is a good candidate for pre-clinical tests as a phytotherapeutic agent or for chemical isolation of the active compounds with the aim of finding new antimalarial drugs.

pfcrt Polymorphism and the spread of chloroquine resistance in Plasmodium falciparum populations across the Amazon Basin.

The widespread occurrence of drug-resistant malaria parasites in South America presents a formidable obstacle to disease control in this region. To characterize parasite populations and the chloroquine-resistance profile of Plasmodium falciparum in the Amazon Basin, we analyzed a DNA segment of the pfcrt gene, spanning codons 72-76, and genotyped 15 microsatellite (MS) markers in 98 isolates from 6 areas of Brazil, Peru, and Colombia where malaria is endemic. The K76T mutation, which is critical for chloroquine resistance, was found in all isolates. Five pfcrt haplotypes (S[tct]MNT, S[agt]MNT, CMNT, CMET, and CIET) were observed, including 1 previously found in Asian/African isolates. MS genotyping showed relatively homogeneous genetic backgrounds among the isolates, with an average of 3.8 alleles per marker. Isolates with identical 15-loci MS haplotypes were found in different locations, suggesting relatively free gene flow across the Amazon Basin. Allopatric isolates carrying SMNT and CMNT haplotypes have similar genetic backgrounds, although parasites carrying the CIET haplotype have some exclusive MS alleles, suggesting that parasites with CIET alleles were likely to have been introduced into Brazil from Asia or Africa. This study provides the first evidence of the Asian pfcrt allele in Brazil and a detailed analysis of P. falciparum populations, with respect to pfcrt haplotypes, in the Amazon Basin.