# Breaking down malaria outbreak: A multidisciplinary approach in a border village of French Guiana

## TL;DR

This study explores why malaria persists in a small village in French Guiana by analyzing human behavior, mosquito patterns, and environmental factors.

## Contribution

The study provides a multidisciplinary analysis of malaria persistence in a border village using entomological, behavioral, and epidemiological data.

## Key findings

- Malaria PCR prevalence was 51% in 2017 and dropped to 16% in 2018.
- Anopheles darlingi mosquitoes were most active in the evening and early morning, with no presence in slash-and-burn fields.
- Most bed nets were improperly maintained, increasing exposure risk before bedtime.

## Abstract

Isolated areas of malaria transmission can persist in countries nearing malaria elimination. To tailor interventions accordingly, smaller-scale surveillance and a deeper understanding of local conditions are needed, including human, environmental and vectorial parameters, and how these parameters interact. This study investigated the potential at-risk situations that could explain the dynamics of malaria persistence in an isolated recurrent high transmission area in French Guiana, using a transdisciplinary approach.

We implemented an ancillary study in Trois-Palétuviers (200 inhabitants), an isolated village in French Guiana bordering Brazil. This was based on two cross-sectional surveys conducted from September to December in 2017 and 2018 that collected both malaria prevalence and behavioural data. Entomological data were collected using 4 Mosquito Magnet traps for three consecutive nights each month. A total of 182 participants were included. The median age was 12.5 years in 2017 (IQR [5;27]). Malaria PCR prevalence was 51% (n = 92) in 2017 and 16% (n = 30) in 2018. Almost all participants used bed nets (99%, n = 180) – but 88% had at least one factor of bed nets ineffectiveness (mainly inadequate drying and washing) –, 63% (n = 114) used indoor insecticides and 32% (n = 57) used skin repellents. Anopheles darlingi, representing 99.7% of the Anopheles caught, were captured throughout the night, with higher abundance in the evening and early morning. No An. darlingi were found in slash-and-burn fields. The high relative abundance of An. darlingi before bedtime exposed inhabitants to the vector’s bites.

The absence of An. darlingi in expected locations, such as slash-and-burn fields, points to the complex ecology of malaria transmission and underscores the need for a nuanced understanding of environmental influences, with continuous surveillance. Cross-description of the data suggests a high risk of exposure to mosquito bites by residents before they are protected by bed nets. The inadequacy of anti-vectorial protective measures could be mitigated by education campaigns about protective tools, and by additional protective tools and a frequent distribution of bed nets.

In areas nearing malaria elimination, where only a few cases remain, these are either sporadically disseminated throughout the country or found in hotspots where epidemics are recurrent. These persisting pockets need to be thoroughly investigated to understand the human, entomological, and environmental conditions that explain their persistence.

Our work focuses on one of these areas in French Guiana, where two micro-epidemics occurred in 2017 and 2018 in a border village of 200-inhabitants. We described the location and nightly dynamics of the main malaria vector in the area, Anopheles darlingi, as well as the potential at-risk and protective human behaviours when and where that vector is present. The inadequacy of anti-vectorial protection for outdoor and evening activities, despite the presence of the vector, highlights the need to supplement bed nets with other acceptable and free protection. New acceptable protection needs to be developed against outdoor bites, with complementary strategies added in the meantime. The persistence of malaria vectors at night indicates that frequent bed net distribution should be maintained, along with education about bed net care. Additionally, education campaigns about protective tools and prompt healthcare-seeking are also required.