Resurgence risk for malaria, characterization of a recent outbreak in a Amazonian border area -French Guiana/Brazil-

Abstract Background In 2017, inhabitants along the border between French Guiana and Brazil were affected by a malaria outbreak primarily due to Plasmodium vivax ( Pv ). While malaria cases have steadily declined between 2005-2016 in this Amazonian region, a resurgence was observed in 2017. Methods Two investigations were performed according to two different spatial scales and type of information details. Firstly, a local study on the French Guiana border, which enabled a thorough investigation of the malaria cases treated at the local village health center and of the entomological situation in the most affected neighborhood and secondly a regional and cross-border study, which enabled exploration of the regional spatial-temporal epidemic dynamic. Number and location of malaria cases were estimated using French and Brazilian surveillance systems. Results On the French Guiana side of the border in Saint Georges de l’Oyapock, the attack rate was 5.5% (n=219/4000), reaching 51.4% (n=90/175) in one Amerindian neighborhood. Entomological findings suggest a peak of Anopheles darlingi density in August and September. Two female An. darlingi (n=2/1104, 0.18%) were found Pv -positive during this peak. During the same period, aggregated data from passive surveillance conducted by Brazilian and French Guianese border health centers identified 1,566 cases of Pv infection. Temporal distribution during the 2007-2018 period displayed seasonal patterns with a peak in November 2017. Four clusters were identified among the epidemic profiles of the localities of the cross-border area. All localities of the first two clusters were Brazilian. The localization of the first cluster suggests an onset of the outbreak in the Amerindian reservation, subsequently expanding to French Amerindian neighborhoods and to non-Native communities. Conclusions The current findings demonstrate a potential increase in malaria cases in an area with otherwise declining numbers. This is a transborder area where human mobility and remote populations challenge malaria control programs. This investigation illustrates the importance of international border surveillance and collaboration for malaria control, particularly in Amerindian villages and mobile populations.