PLASMODIUM vivax malaria is challenging long-standing assumptions about human resistance, with new evidence showing infections occurring in individuals previously thought to be largely protected.
The parasitic disease, transmitted by mosquitoes and capable of causing recurring fevers due to dormant liver stages known as hypnozoites, has been detected in Duffy-negative populations in Sudan.1,2
Rising Infections Despite Presumed Protection
Sudan has been reporting increasing Plasmodium vivax malaria cases even though a large proportion of the population carries the Duffy-negative blood group, historically considered protective against the parasite.¹ This emerging pattern has prompted closer investigation into whether the biological barrier is less absolute than previously believed.
Evidence From Two Decades of Data
A systematic review of 16 studies conducted between 2005 and 2025, covering 5,753 individuals across Sudan, found infections in both Duffy-positive and Duffy-negative groups.¹ Meta-analysis of five studies showed a pooled prevalence of 11.7% among Duffy-negative individuals (95% CI 7.2–17.3%), indicating measurable infection levels even in this group.
Parasite Adaptation and Genetic Diversity
The findings also point to considerable genetic variation in the parasite’s Duffy Binding Protein, including multiple haplotypes and gene duplications that may support infection in Duffy-negative hosts.¹ These adaptations could reflect evolutionary pressure enabling the parasite to bypass previously effective host barriers.
Relapse Biology Complicates Control
Beyond host–parasite interaction, P. vivax has intrinsic biological features that complicate elimination. Dormant liver-stage hypnozoites can reactivate weeks or months after infection, driving repeated episodes of parasitaemia without new mosquito bites.² These relapses may account for 40–77% of clinical infections in some endemic settings, and a proportion of cases may remain asymptomatic.²
Implications for Malaria Elimination Efforts
Together, the findings suggest that Duffy negativity may not provide complete protection against Plasmodium vivax malaria. They also highlight the importance of integrating molecular surveillance with host–parasite genomic data to better track transmission and inform elimination strategies.¹ Improved diagnostic sensitivity and strategies addressing relapse biology may be necessary to reduce hidden reservoirs of infection and support long-term control efforts.
References
- Elfaki M et al. Plasmodium vivax infection in Duffy-negative populations in Sudan: a systematic review and meta-analysis of host–parasite genetic adaptation. Malar J. 2026;DOI:10.1186/s12936-026-05923-y.
- Tadesse FG et al. Parasite and gametocyte dynamics and infectivity to mosquitoes during recurrent Plasmodium vivax infections; a longitudinal study from Ethiopia. J Infect. 2026; DOI:10.1016/j.jinf.2026.106756.
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