Malaria in Gold Miners in the Guianas and the Amazon: Current Knowledge and Challenges

“Purpose of Review Following Paraguay and Argentina, several countries from the Amazon region aim to eliminate malaria. To achieve this, all key affected and vulnerable populations by malaria, including people working on gold mining sites, must be considered. What is the situation of malaria in these particular settings and what are the challenges? This literature review aims to compile knowledge to answer these questions. Recent Findings The contexts in which gold miners operate are very heterogeneous: size and localization of mines, links with crime, administrative status of the mines and of the miners, mobility of the workers or national regulations. The number of malaria cases has been correlated with deforestation (Brazil, Colombia), gold production (Colombia), gold prices (Guyana), or location of the mining region (Peru, Colombia, Venezuela, Guyana). The burden of malaria in gold mines differs between territories: significant in Guyana, French Guiana, or Venezuela; lower in Brazil. Although Plasmodium vivax causes 75% of malaria cases in the Americas, P. falciparum is predominant in several gold mining regions, especially in the Guiana Shield. Because of the remoteness from health facilities, self-medication with under-the-counter antimalarials is frequent. This consti- tutes a significant risk for the emergence of new P. falciparum parasites resistant to antimalarial drugs. Summary Because of the workers’ mobility, addressing malaria transmission in gold mines is essential, not only for miners, but also to prevent the (re-)emergence of malaria. Strategies among these populations should be tailored to the context because of the heterogeneity of situations in different territories. The transnational environment favoring malaria transmission also requires transborder and regional cooperation, where innovative solutions should be considered and evaluated

High Performance of Histidine-Rich Protein 2 Based Rapid Diagnostic Tests in French Guiana are Explained by the Absence of pfhrp2 Gene Deletion in P. falciparum

BACKGROUND: Care for malaria patients in endemic areas has been improved through the increasing use of Rapid Diagnostic Tests (RDTs). Most RDTs target the histidine-rich protein-2 antigen (PfHRP2) to detect P. falciparum, as it is abundant and shows great heat stability. However, their use in South America has been widely questioned following a recent publication that pinpoints the high prevalence of Peruvian field isolates lacking the gene encoding this protein. In the remote rural health centers of French Guiana, RDTs are the main diagnosis tools. Therefore, a study of PfHRP2 RDT performances and pfhrp2 genotyping was conducted to determine whether a replacement of the current pLDH-based kit could be considered. METHODS: The performance study compared the SD Malaria Ag test P.f/Pan® kit with the current gold standard diagnosis by microscopy. The prevalence of pfhrp2 and pfhrp3 deletions were evaluated from 221 P. falciparum isolates collected between 2009 and 2011 in French Guiana. RESULTS: Between January 2010 and August 2011, 960 suspected cases of malaria were analyzed using microscopy and RDTs. The sensitivity of the SD Malaria Ag test P.f/Pan® for detection of P. falciparum was 96.8% (95% CI: 90.9-99.3), and 86.0% (95% CI: 78.9-91.5) for the detection of P. vivax. No isolates (95% CI: 0-4.5) lacking either exon of the pfhrp2 gene were identified among the 221 P. falciparum isolates analyzed, but 7.4% (95% CI: 2.8-15.4) lacked the exon 2 part of the pfhrp3 gene. CONCLUSIONS: Field isolates lacking either exon of the pfhrp2 gene are absent in this western part of South America. Despite its sensibility to detect P. vivax, the SD Malaria Ag test P.f/Pan® kit is a satisfying alternative to microscopy in remote health centers, where it is difficult to provide highly skilled microscopists and to maintain the necessary equipment

COIL: a methodology for evaluating malarial complexity of infection using likelihood from single nucleotide polymorphism data.

International audienceComplex malaria infections are defined as those containing more than one genetically distinct lineage of Plasmodium parasite. Complexity of infection (COI) is a useful parameter to estimate from patient blood samples because it is associated with clinical outcome, epidemiology and disease transmission rate. This manuscript describes a method for estimating COI using likelihood, called COIL, from a panel of bi-allelic genotyping assays. COIL assumes that distinct parasite lineages in complex infections are unrelated and that genotyped loci do not exhibit significant linkage disequilibrium. Using the population minor allele frequency (MAF) of the genotyped loci, COIL uses the binomial distribution to estimate the likelihood of a COI level given the prevalence of observed monomorphic or polymorphic genotypes within each sample. COIL reliably estimates COI up to a level of three or five with at least 24 or 96 unlinked genotyped loci, respectively, as determined by in silico simulation and empirical validation. Evaluation of COI levels greater than five in patient samples may require a very large collection of genotype data, making sequencing a more cost-effective approach for evaluating COI under conditions when disease transmission is extremely high. Performance of the method is positively correlated with the MAF of the genotyped loci. COI estimates from existing SNP genotype datasets create a more detailed portrait of disease than analyses based simply on the number of polymorphic genotypes observed within samples. The capacity to reliably estimate COI from a genome-wide panel of SNP genotypes provides a potentially more accurate alternative to methods relying on PCR amplification of a small number of loci for estimating COI. This approach will also increase the number of applications of SNP genotype data, providing additional motivation to employ SNP barcodes for studies of disease epidemiology or control measure efficacy. The COIL program is available for download from GitHub, and users may also upload their SNP genotype data to a web interface for simple and efficient determination of sample COI

Evolution of Fitness Cost-Neutral Mutant PfCRT Conferring P. falciparum 4-Aminoquinoline Drug Resistance Is Accompanied by Altered Parasite Metabolism and Digestive Vacuole Physiology

Southeast Asia is an epicenter of multidrug-resistant Plasmodium falciparum strains. Selective pressures on the subcontinent have recurrently produced several allelic variants of parasite drug resistance genes, including the P. falciparum chloroquine resistance transporter (pfcrt). Despite significant reductions in the deployment of the 4-aminoquinoline drug chloroquine (CQ), which selected for the mutant pfcrt alleles that halted CQ efficacy decades ago, the parasite pfcrt locus is continuously evolving. This is highlighted by the presence of a highly mutated allele, Cam734 pfcrt, which has acquired the singular ability to confer parasite CQ resistance without an associated fitness cost. Here, we used pfcrt-specific zinc-finger nucleases to genetically dissect this allele in the pathogenic setting of asexual blood-stage infection. Comparative analysis of drug resistance and growth profiles of recombinant parasites that express Cam734 or variants thereof, Dd2 (the most common Southeast Asian variant), or wild-type pfcrt, revealed previously unknown roles for PfCRT mutations in modulating parasite susceptibility to multiple antimalarial agents. These results were generated in the GC03 strain, used in multiple earlier pfcrt studies, and might differ in natural isolates harboring this allele. Results presented herein show that Cam734-mediated CQ resistance is dependent on the rare A144F mutation that has not been observed beyond Southeast Asia, and reveal distinct impacts of this and other Cam734-specific mutations on CQ resistance and parasite growth rates. Biochemical assays revealed a broad impact of mutant PfCRT isoforms on parasite metabolism, including nucleoside triphosphate levels, hemoglobin catabolism and disposition of heme, as well as digestive vacuole volume and pH. Results from our study provide new insights into the complex molecular basis and physiological impact of PfCRT-mediated antimalarial drug resistance, and inform ongoing efforts to characterize novel pfcrt alleles that can undermine the efficacy of first-line antimalarial drug regimens

Contribution to the study of Plasmodium falciparum resistance to atovaquone-proguanil

Mai 2006The recurrent emergence and spread of multidrug-resistant Plasmodium falciparum delays the control of malaria. Since 2000, a safe and efficient new combination, atovaquone-proguanil, has rapidly became the first line antimalarial drug in most European infectious diseases wards. This work aimed to better understand falciparum resistance to atovaquone-proguanil. The copy number of the cytochrome b gene, pfcytb, the main atovaquone-proguanil target, was evaluated by real-time PCR at 16 ± 9 copies per parasite. No natural resistance to atovaquone/proguanil was detected by in vitro phenotyping in West African and Indian Ocean isolates although therapeutic failures were observed. The majority of early therapeutic failures were linked to poor drug absorption while late therapeutic failures were associated with day failure parasites highly resistant in vitro and carrying a pfcytb mutation (Y268S or Y268C) without any amplification of pfcytb gene. Mitochondrial genome sequencing associated with microsatellite marker analysis of parasites from before and after parasite recrudescence show that these mutations had appeared independently within each of the six patients experiencing a therapeutic failure. With falciparum resistance being less than 0.1%, atovaquone-proguanil is efficient for treatment of travellers experiencing malaria. As resistance emerged within patient without risk of transmission, resistance spread has not begun. Combination with an antimalarial drug having a different target should be a prerequisite of deployment in endemic areas.L'apparition récurrente de Plasmodium falciparum résistant aux antipaludiques est un obstacle majeur au contrôle du paludisme. Introduite en 2000, une nouvelle association très bien tolérée, l'atovaquone-proguanil est rapidement devenue le traitement de choix des accès palustres simples dans certains hôpitaux français. Ce travail de recherche avait pour objectif d'approfondir les connaissances sur la résistance à cette association. Nous n'avons détecté aucune résistance naturelle à l'atovaquone-proguanil en Afrique de l'Ouest et dans l'Océan Indien parmi 477 isolats. La majorité des rechutes précoces sont liées à une malabsorption des principes actifs alors que les échecs tardifs sont liés à la présence de parasites hautement résistants in vitro présentant, au moment de la rechute, une mutation au niveau du codon 268 du cytochrome b (Y268S ou Y268C) sans augmentation du nombre de copies de ce gène, évalué par PCR en temps réel à 16 ± 9 copies par parasite. Le séquençage du génome mitochondrial et l'analyse de marqueurs microsatellites chromosomiques des parasites isolés avant et après la rechute parasitaire montrent que la mutation associée à cette résistance est apparue indépendamment chez chacun des six patients en échec étudiés. L'atovaquone-proguanil est efficace pour le traitement des voyageurs avec moins de 0,1% de résistance. Le risque actuel de dispersion des résistances est négligeable puisqu'elles émergent chez des patients traités hors de zone de transmission. Par contre, si cette association devait être déployée en zone d'endémie, il serait indispensable de la combiner avec d'autres molécules