Assessment of Plasmodium vivax transmission and asymptomatic carriage risk among artisanal gold miners in western French Guiana, 2014-2020.

Background: The final challenge for malaria elimination in many countries is to interrupt the circulation of Plasmodium vivax. Given the unique biology of this parasite, innovative approaches are imperative, with a focus on identifying asymptomatic carriers of dormant parasite forms. This article delineates the recent epidemiological patterns of P. vivax malaria within a highly mobile and hard-to-reach population in the Guiana Shield. It further proposes an assessment of the potential reservoir of asymptomatic carriers.

Methods: This analysis was based on data from: (i) two cross-sectional surveys carried out at the French-Surinamese border in 2015 and 2019, including adults returning from gold mining sites located in French Guiana (FG), [questionnaires and blood samples, tested for polymerase chain reaction (PCR) and P. vivax serological exposure markers (SEM) of recent infection]; (ii) epidemiological malaria surveillance system in Suriname, including cases imported from gold mining sites located in western FG between 2014 and 2020. Factors associated with P. vivax seropositivity were analysed by multiple logistic regression. The probability of carrying P. vivax parasites (blood-stage or hypnozoite) was estimated by a classification drawn from PCR results, SEM and reported recent history of illness.

Results: Surveillance data showed a decrease in malaria imported cases from French Guiana between beginning and end of the analysed period (236 in 2014 to 74 in 2020) and an increase in the proportion of cases associated with P. vivax (52.4% in 2014 to 100% in 2020). The PCR-prevalence of P. vivax in survey samples decreased from 11.4% in 2015 to 4.0% in 2019; P. vivax seropositivity decreased from 44.7% to 28.4%. P. vivax seropositivity was positively associated with male sex, age and number of years spent in gold mining, type of activity, and reported malaria history (episode within less than nine months OR = 10.73, 95% CI: 5.87-19.6, or history of repeated older episodes OR = 5.31, 95% CI: 3.13-9.01).

Conclusions: Our analysis shows an epidemiological evolution typical of a scenario of decreasing malaria circulation. Nevertheless, in 2020, gold miners in western FG still showed a moderate level of P. vivax circulation. Biological methods and epidemiological criteria can help to select potential parasite carriers, who could benefit from targeted drug administration.