| Summary: | <p>Over a third of the world’s population lives at risk of potentially severe <em>Plasmodium vivax</em> malaria. Unique aspects of this parasite’s biology and interactions with its human host make it harder to control and eliminate than the better studied <em>Plasmodium falciparum</em> parasite. Spatial mapping of two human genetic polymorphisms were developed to support evidence-based targeting of control interventions and therapies.</p> <p>First, to enumerate and map the population at risk of <em>P. vivax</em> infection (P<em>v</em>PAR), the prevalence of this parasite’s human blood cell receptor – the Duffy antigen – was mapped globally. Duffy negative individuals are resistant to infection, and this map provided the means to objectively model the low endemicity of <em>P. vivax</em> across Africa. The Duffy maps helped resolve that only 3% of the global <em>Pv</em>PAR was from Africa.</p> <p>The second major research focus was to map the spatial distribution of glucose-6-phosphate dehydrogenase enzyme deficiency (G6PDd), the genetic condition which predisposes individuals to potentially life-threatening haemolysis from primaquine therapy. Despite this drug’s vital role in being the only treatment of relapsing <em>P. vivax</em> parasites, risks of G6PDd-associated haemolysis result in significant under-use of primaquine. G6PDd was found to be widespread, with an estimated frequency of 8.0% (50% CI: 7.4-8.8%) across malarious regions.</p> <p>Third, it was important to represent more detailed descriptions of the genetic diversity underpinning this enzyme disorder, which ranges in phenotype from expressing mild to life-threatening primaquine-induced haemolysis. These variants’ spatial distributions were mapped globally and showed strikingly conspicuous distributions, with widespread A- dominance across Africa, predominance of the Mediterranean variant from the Middle East across to India, and east of India diversifying into a different and diverse array of variants, showing heterogeneity both at regional and community levels.</p> <p>Fourth, the G6PDd prevalence and severity maps were synthesised into a framework assessing the spatial variability of overall risk from G6PDd to primaquine therapy. This found that risks from G6PDd were too widespread and potentially severe to sanction primaquine treatment without prior G6PDd screening, particularly across Asia where the majority of the population are Duffy positive and G6PDd was common and severe.</p> <p>Finally, the conclusions from these studies were discussed and recommendations made for essential further research needed to support current efforts into <em>P. vivax</em> control.</p>
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