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

Background: 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.

Methodology/principal findings: 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.

Conclusions/significance: 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.