Multidrug-resistant parasites from the Amazon region caused the outbreak in the northern coastal region.

BackgroundA major concern in malaria vaccine development is genetic polymorphisms typically observed among Plasmodium isolates in different geographical areas across the world. Highly polymorphic regions have been observed in Plasmodium falciparum and Plasmodium vivax antigenic surface proteins such as Circumsporozoite protein (CSP), Duffy-binding protein (DBP), Merozoite surface protein-1 (MSP-1), Apical membrane antigen-1 (AMA-1) and Thrombospondin related anonymous protein (TRAP).MethodsGenetic variability was assessed in important polymorphic regions of various vaccine candidate antigens in P. vivax among 106 isolates from the Amazon Region of Loreto, Peru. In addition, genetic diversity determined in Peruvian isolates was compared to population studies from various geographical locations worldwide.ResultsThe structured diversity found in P. vivax populations did not show a geographic pattern and haplotypes from all gene candidates were distributed worldwide. In addition, evidence of balancing selection was found in polymorphic regions of the trap, dbp and ama-1 genes.ConclusionsIt is important to have a good representation of the haplotypes circulating worldwide when implementing a vaccine, regardless of the geographic region of deployment since selective pressure plays an important role in structuring antigen diversity.

BackgroundSulfadoxine-pyrimethamine was a common first line drug therapy to treat uncomplicated falciparum malaria, but increasing therapeutic failures associated with the development of significant levels of resistance worldwide has prompted change to alternative treatment regimes in many national malaria control programs.Methodology and FindingWe conducted an in vivo therapeutic efficacy trial of sulfadoxine-pyrimethamine at two locations in the Peruvian Amazon enrolling 99 patients of which, 86 patients completed the protocol specified 28 day follow up. Our objective was to correlate the presence of polymorphisms in P. falciparum dihydrofolate reductase and dihydropteroate synthase to in vitro parasite susceptibility to sulfadoxine and pyrimethamine and to in vivo treatment outcomes. Inhibitory concentration 50 values of isolates increased with numbers of mutations (single [108N], sextuplet [BR/51I/108N/164L and 437G/581G]) and septuplet (BR/51I/108N/164L and 437G/540E/581G) with geometric means of 76 nM (35–166 nM), 582 nM (49-6890- nM) and 4909 (3575–6741 nM) nM for sulfadoxine and 33 nM (22–51 nM), 81 nM (19–345 nM), and 215 nM (176–262 nM) for pyrimethamine. A single mutation present in the isolate obtained at the time of enrollment from either dihydrofolate reductase (164L) or dihydropteroate synthase (540E) predicted treatment failure as well as any other single gene alone or in combination. Patients with the dihydrofolate reductase 164L mutation were 3.6 times as likely to be treatment failures [failures 85.4% (164L) vs 23.7% (I164); relative risk = 3.61; 95% CI: 2.14 – 6.64] while patients with the dihydropteroate synthase 540E were 2.6 times as likely to fail treatment (96.7% (540E) vs 37.5% (K540); relative risk = 2.58; 95% CI: 1.88 – 3.73). Patients with both dihydrofolate reductase 164L and dihydropteroate synthase 540E mutations were 4.1 times as likely to be treatment failures [96.7% vs 23.7%; RR = 4.08; 95% CI: 2.45 – 7.46] compared to patients having both wild forms (I164 and K540).ConclusionsIn this part of the Amazon basin, it may be possible to predict treatment failure with sulfadoxine-pyrimethamine equally well by determination of either of the single mutations dihydrofolate reductase 164L or dihydropteroate synthase 540E.Trial RegistrationClinicalTrials.gov NCT00951106 NCT00951106

In the Peruvian North Coast (PNC), the number of malaria cases increased steadily from 2007 to 2010 despite a significant decline in the overall number of cases in Peru during the same period. To better understand the transmission dynamics of populations in the PNC and the neighboring Ecuadorian Amazon Basin (EAB), we studied the genetic variability and population structure of in these areas. One hundred and twenty isolates (58 from Piura and 37 from Tumbes in the PNC collected from 2008 to 2010 and 25 from the EAB collected in Pastaza from 2001 to 2004) were assessed by five polymorphic microsatellite markers. Genetic variability was determined by expected heterozygosity () and population structure by Bayesian inference cluster analysis. We found very low genetic diversity in the PNC ( = 0-0.32) but high genetic diversity in the EAB ( = 0.43-0.70). Population structure analysis revealed three distinct populations in the three locations. Six of 37 (16%) isolates from Tumbes had an identical haplotype to that found in Piura, suggesting unidirectional flow from Piura to Tumbes. In addition, one haplotype from Tumbes showed similarity to a haplotype found in Pastaza, suggesting that this could be an imported case from EAB. These findings strongly suggest a minimal population flow and different levels of genetic variability between these two areas divided by the Andes Mountains. This work presents molecular markers that could be used to increase our understanding of regional malaria transmission dynamics, which has implications for the development of strategies for control.

BackgroundPlasmodium vivax (Pv) represents the most geographically widespread human malaria parasite. Targeting the pre-erythrocytic (PE) stage of the parasite life cycle is especially appealing for Pv vaccines as it would prevent disease and transmission. Here, we explore naturally acquired immunity to a panel of Pv PE antigens as a first step to enable vaccine development and to better understand naturally-acquired PE immunity.MethodsHumoral and cellular immunity were evaluated by ELISA and ELISpot, using samples from Pv infected individuals from a low endemic malaria region in the Peruvian Amazon Basin. In addition, we utilized experimental infection of Aotus non-human primates with Pv or P. falciparum (Pf) in order to evaluate the contribution of blood stage infection to the humoral response observed in human samples.ResultsIn our clinical samples, twelve PE antigens showed positive antibody reactivity with variable prevalence of 58–99%. The magnitude of the IgG antibody response against PE antigens was lower compared with blood stage antigens MSP1 and DBP-II although titers persisted better for PE antigens, six months later after infection (average decrease of 6% for PE antigens and 43% for MSP1) in general. A significant correlation between IgG antibodies and number of previous malaria episodes was observed only for blood stage antigens. High IgG responders across PE and blood stage antigens showed a significantly lower parasitemia compared to low responders (median 1873 vs 4663 par/µl). We observed a positive T cell response in 35% vs 9–35% of total volunteers against blood stage antigen MSP1 and PE antigens, respectively, and saw no correlation with IgG responses. Aotus monkeys infected with Pv blood stage showed positive reactivity against the seven PE antigens tested. In contrast, only 2 of 10 monkeys infected with Pf showed low positive IgG cross-reactivity against Pv MSP1 and none of which cross-reacted to Pv CSP.ConclusionsOur results demonstrate clear humoral and T cell responses against Pv PE antigens in individuals naturally infected with P. vivax. In addition, these results are largely replicated in a novel Aotus nancymaae Pv blood stage challenge model which suggest a contribution from blood stages to PE cross-reactivity. Together, these data clearly identify novel attractive PE antigens suitable for use in the development of new malaria vaccine candidates.