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Background <p>Ecuador is approaching malaria elimination, but its Amazonian Putumayo canton borders regions in Colombia and Peru with high transmission intensity. This ‘frontier’ setting represents a critical vulnerability where asymptomatic infections may sustain transmission, undetected by routine surveillance.</p> Methods <p>In a repeated cross-sectional study during the 2023 rainy season, we surveyed 293 asymptomatic individuals in four riverine communities in Putumayo. We used a tiered diagnostic approach: rapid diagnostic tests (RDTs), expert microscopy, and real-time qPCR targeting the 18S rRNA gene.</p> Results <p>No infections were detected by RDT (0/293). Microscopy identified three <i>P. vivax</i> infections (1.0%, 95% CI 0.2–2.4%). qPCR detected five positive cases (1.7%, 95% CI 0.6–3.9%), revealing two additional submicroscopic infections. The failure of a subsequent species-specific PCR and high Cq values (mean 32.6) indicated very low parasite densities. Infections were found only in the mid-to-late rainy season, predominantly in males.</p> Conclusions <p>Molecular surveillance revealed a low-density, asymptomatic malaria reservoir missed entirely by RDTs, and partially by microscopy. This hidden burden represents a critical blind spot for Ecuador’s elimination program. To achieve and sustain elimination, surveillance in such border regions must incorporate highly sensitive molecular tools and be supported by robust cross-border collaboration.</p>

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Asymptomatic parasitaemia in a malaria pre-elimination setting in the Putumayo area of the Ecuadorian Amazon basin

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月18日

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  • Jacob van der Ende,
  • M. Vanessa Dávila,
  • Sandra Menting,
  • Fabián E. Sáenz,
  • Thomas Hanscheid,
  • Henk D. F. H. Schallig,
  • Martin P. Grobusch

摘要

Background

Ecuador is approaching malaria elimination, but its Amazonian Putumayo canton borders regions in Colombia and Peru with high transmission intensity. This ‘frontier’ setting represents a critical vulnerability where asymptomatic infections may sustain transmission, undetected by routine surveillance.

Methods

In a repeated cross-sectional study during the 2023 rainy season, we surveyed 293 asymptomatic individuals in four riverine communities in Putumayo. We used a tiered diagnostic approach: rapid diagnostic tests (RDTs), expert microscopy, and real-time qPCR targeting the 18S rRNA gene.

Results

No infections were detected by RDT (0/293). Microscopy identified three P. vivax infections (1.0%, 95% CI 0.2–2.4%). qPCR detected five positive cases (1.7%, 95% CI 0.6–3.9%), revealing two additional submicroscopic infections. The failure of a subsequent species-specific PCR and high Cq values (mean 32.6) indicated very low parasite densities. Infections were found only in the mid-to-late rainy season, predominantly in males.

Conclusions

Molecular surveillance revealed a low-density, asymptomatic malaria reservoir missed entirely by RDTs, and partially by microscopy. This hidden burden represents a critical blind spot for Ecuador’s elimination program. To achieve and sustain elimination, surveillance in such border regions must incorporate highly sensitive molecular tools and be supported by robust cross-border collaboration.