| Summary: | <p>Abstract</p> <p>Background</p> <p>There is large body of evidence that states that invasion of <it>Plasmodium vivax</it> requires the Duffy antigen, but the universality of this specificity is certainly now under question with recent reports showing that in some parts of the world <it>P</it>. <it>vivax</it> infects and causes disease in Duffy-negative people. These findings reinforce the idea that this parasite is rapidly evolving, being able to use other receptors than Duffy to invade the erythrocytes, which may have an enormous impact in <it>P</it>. <it>vivax</it> current distribution. The presence of <it>P</it>. <it>vivax</it> infection in Duffy-negative individuals was investigated in a cross-sectional study conducted in Anajás, Archipelago of Marajó, State of Pará, which is an area of malaria transmission in the Brazilian Amazonia.</p> <p>Methods</p> <p>Duffy genotyping and <it>Plasmodium</it> species diagnostic assays were performed successfully in 678 individuals. An allele-specific primer polymerase chain reaction (PCR) technique was used for Duffy blood group genotyping. Identification of <it>Plasmodium</it> species was achieved by conventional blood smear light microscopy and a TaqMan-based real-time PCR method to detect mitochondrial genome of <it>Plasmodium falciparum</it> and <it>P</it>. <it>vivax</it>.</p> <p>Results</p> <p><it>Plasmodium spp</it>. infection was detected in 137 samples (20.2%). Prevalence of each <it>Plasmodium</it> species was 13.9% <it>P</it>. <it>vivax</it>, 5.8% <it>P</it>. <it>falciparum</it>, and 0.6% <it>P</it>. <it>vivax</it> plus <it>P</it>. <it>falciparum</it>. Overall, 4.3% (29/678) were genotyped as Duffy-negative (<it>FY</it>*<it>B</it><sup><it>ES</it></sup>/*<it>B</it><sup><it>ES</it></sup>). Among Duffy-negative individuals 6.9% were <it>P</it>. <it>vivax</it> PCR positive and among Duffy-positive 14.2% were <it>P</it>. <it>vivax</it> PCR positive. Although lower, the risk of Duffy-negatives to experience a <it>P</it>. <it>vivax</it> blood stage infection was not significantly different to that of Duffy-positives. Furthermore, the genotypic and allelic frequencies of the Duffy blood group among <it>P</it>. <it>vivax</it>-infected patients and in the control group did not differ significantly, also suggesting no reduction in infection rates among the carriers of <it>FY</it>*<it>B</it><sup><it>ES</it></sup> allele.</p> <p>Conclusions</p> <p>The data obtained in Anajás showed no differential resistance vivax malaria among Duffy-negative and Duffy-positive individuals. This result needs additional confirmation through a deeper evaluation in a larger sample of patients with <it>P</it>. <it>vivax</it> malaria and molecular parasite characterization. Nonetheless, this genetic profile of the parasite may be contributing to the high incidence of malaria in the municipality.</p>
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