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Background There is large body of evidence that states that invasion of Plasmodium vivax 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 P. vivax 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 P. vivax current distribution. The presence of P. vivax 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. Methods Duffy genotyping and Plasmodium 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 Plasmodium species was achieved by conventional blood smear light microscopy and a TaqMan-based real-time PCR method to detect mitochondrial genome of Plasmodium falciparum and P. vivax. Results Plasmodium spp. infection was detected in 137 samples (20.2%). Prevalence of each Plasmodium species was 13.9% P. vivax, 5.8% P. falciparum, and 0.6% P. vivax plus P. falciparum. Overall, 4.3% (29/678) were genotyped as Duffy-negative (FY*B ES /*B ES ). Among Duffy-negative individuals 6.9% were P. vivax PCR positive and among Duffy-positive 14.2% were P. vivax PCR positive. Although lower, the risk of Duffy-negatives to experience a P. vivax blood stage infection was not significantly different to that of Duffy-positives. Furthermore, the genotypic and allelic frequencies of the Duffy blood group among P. vivax-infected patients and in the control group did not differ significantly, also suggesting no reduction in infection rates among the carriers of FY*B ES allele. Conclusions 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 P. vivax malaria and molecular parasite characterization. Nonetheless, this genetic profile of the parasite may be contributing to the high incidence of malaria in the municipality.

Background The Philippines is among the 39 countries aiming for malaria elimination. The major challenge is finding residual transmission foci in difficult to access villages of Southern Mindanao, Philippines. The sensitivity of microscopy to detect asymptomatic infections declines with decreasing malaria prevalence. The aim of this project is to use antibody markers of P. falciparum and P. vivax infection to locate residual transmission foci and to determine effects of control measures in Sarangani Province, the Philippines.

Major progress has been made in reducing the burden of malaria in the Solomon Islands and Vanuatu. This has been achieved by improving health systems, increasing deployment of ITN, improving diagnostics, and by deployment of more effective antimalarials, including ACT. These advances have highlighted the challenges in achieving elimination of malaria in these countries, and may provide useful lessons for other settings where control activities are less advanced. Specific challenges include the significant prevalence of submicroscopic parasitemia that can only be detected by molecular methods such as PCR. This poses significant challenges to active case detection and to programmatic needs to monitor progress in elimination. As well, the significant prevalence of asymptomatic submicroscopic parasitemia in an epidemiological setting where herd immunity is waning raises questions regarding the nature of anti-disease immunity in such settings. Further, the relative prevalence of P. vivax infection is increasing compared to P. falciparum. A specific challenges this poses is the need to address the issue of latent liver stage infection with hypnozoites in a setting where the prevalence of clinically significant G6PD deficiency exceeds 10%. In this presentation these challenges all be discussed along with research underway to address them.