# Presence of Dengue Virus NS1 antigen and IgM and IgG antibodies in asymptomatic individuals in Ecuadorian Amazonia - a descriptive repeated cross-sectional community-based survey

## TL;DR

A study in Ecuador's Amazon region found dengue virus transmission in remote river communities, showing the need for community-based testing beyond hospitals.

## Contribution

The study reveals dengue transmission in remote riverine communities, highlighting the importance of community-based surveillance for arboviruses.

## Key findings

- 8.5% of asymptomatic individuals had acute or recent dengue infection.
- Remote riverine communities showed a higher proportion of acute infections compared to urban areas.
- Dengue transmission extends beyond hospital-detected cases into boat-access-only communities.

## Abstract

As malaria approaches elimination in Ecuadorian Amazonia, dengue virus (DENV) has emerged as the dominant vector-borne disease. A recent study documented circulation of DENV in the Putumayo northern border region, but could not determine whether transmission extended beyond road-connected areas into remote riverine communities. We conducted a community-based assessment to quantify dengue virus transmission across an urban–riverine gradient.

This repeated cross-sectional community-based survey screened in total 293 asymptomatic individuals in four communities with, in total, an estimated 4.240 inhabitants along the Putumayo River during the 2023 rainy season. Participants were tested using an NS1/IgM/IgG combination rapid diagnostic test. Acute or recent infection was defined as NS1 and/or IgM positivity; past exposure as IgG-only positivity.

Overall, 8.5% (25/293) of asymptomatic participants had acute or recent DENV infection, and 28.7% (84/293) showed any serological evidence of exposure. The road-connected hub Puerto El Carmen had the highest total prevalence (50.9%), predominantly representing past infection (IgG-only: 42.5%). In contrast, remote riverine communities showed lower overall exposure but a higher proportion of acute/recent infections among positives—reaching 60% in Puerto Rodríguez—suggesting recent viral introduction into immunologically naïve populations.

Dengue virus transmission in the Putumayo Amazonia region extends beyond hospital-detected cases into river-access-only communities. The inverted ratio of acute-to-past infection between urban and riverine settlements suggests source-sink dynamics with ongoing viral movement along fluvial networks. As malaria elimination progresses, integrated arboviral surveillance incorporating community-based RDT screening and field laboratories is essential to detect emerging viral transmission invisible to facility-based systems.

•In a serial cross-sectional community survey, 293 dengue-asymptomatic individuals in four communities along the Putumayo River were screened.•Dengue transmission in the Putumayo region of Ecuadorian Amazonia extends beyond hospital-detected cases into communities only accessible by boat.•The inverted ratio of acute to past infection between urban and riverine settlements suggests viral exportation along fluvial networks.•Arboviral surveillance incorporating community-based RDT screening is essential to detect transmission invisible to hospital-based systems.

In a serial cross-sectional community survey, 293 dengue-asymptomatic individuals in four communities along the Putumayo River were screened.

Dengue transmission in the Putumayo region of Ecuadorian Amazonia extends beyond hospital-detected cases into communities only accessible by boat.

The inverted ratio of acute to past infection between urban and riverine settlements suggests viral exportation along fluvial networks.

Arboviral surveillance incorporating community-based RDT screening is essential to detect transmission invisible to hospital-based systems.