What is it about?

Are repeatedly infected people in vivax malaria settings just unlucky? The burden of many infections in communities follows the 20/80 rule or Pareto principle: 20% of the people account for 80% or more of all infections. The Pareto rule also applies to infections with Plasmodium vivax, the most common cause of malaria in the Amazon and in parts of Asia. Importantly, high-risk individuals – or “malarious persons” –may also be malaria super-spreaders: they contribute disproportionally to parasite transmission to mosquito vectors, which in turn will infect other humans. High-risk people represent a priority target for more intensive interventions to achieve malaria elimination, but identifying them is not a trivial task. Importantly, malarious persons eventually develop clinical immunity, even in areas with very low or residual malaria transmission. As a consequence, they constitute a large but clinically silent parasite reservoir. They maintain low-grade and symptomless chronic infections that remain undiagnosed and untreated, but can still infect mosquitoes and fuel malaria transmission.

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Why is it important?

Understanding the sources of individual variation in the risk of P. vivax infection and disease is critical for identifying population groups that harbor a substantial fraction of the clinical burden of malaria and contribute disproportionally to transmission. Some of factors that modulate malaria risk are genetic – e.g., human polymorphisms known to reduce the susceptibility to P. vivax infection (e.g., Duffy blood group negativity) or affect the efficacy of the treatment used to prevent parasite relapses leading to repeated blood-stage infections (e.g., low-activity variants of the CYP2D6 enzyme). Others are non-genetic (e.g., behavioral, occupational) and therefore are potentially modifiable. Once modifiable risk factors are identified, more cost-effective interventions can be specifically designed toward malaria elimination.


We present an overview of the factors that modulate the individual's risk of P. vivax infection and examine similarities and differences with what is known about the heterogeneity of risk for P. falciparum, the dominant malaria parasite in Africa. We highlight some malaria resistance factors that are “vivax-specific”. We argue that mathematical models of P. vivax malaria must consider individual risk variation in order to estimate the impact of control interventions, especially those selectively targeted at individuals at increased risk of repeated infections.

Rodrigo M. Corder
University of California Berkeley

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This page is a summary of: Individual variation in Plasmodium vivax malaria risk: Are repeatedly infected people just unlucky?, PLoS Neglected Tropical Diseases, January 2023, PLOS, DOI: 10.1371/journal.pntd.0011020.
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