Epidemiology of Leprosy in French Guiana

Rationale: Leprosy (also known as Hansen's disease) is a chronic infection caused by intracellular mycobacteria, Mycobacterium leprae and Mycobacterium lepromatosis (discovered in 2008), preferentially affecting the skin and peripheral nervous system. The disease in humans is potentially disabling and stigmatising.

The modes of transmission of leprosy are not yet fully understood, although it is generally accepted that the main mode of transmission is human-to-human. Apart from humans, the only other major confirmed animal reservoir of M. leprae is the 9-banded armadillo Dasypus novemcinctus, which is found only in the Americas. Recent studies in the southern United States suggest transmission of M. leprae between D. novemcinctus and humans, where 64% of human cases may be attributable to armadillos. Uncertainties remain regarding the zoonotic nature of the disease outside the US and the precise mode of transmission.

The disease is endemic on the American continent where 92% of new cases come from Brazil. In French Guiana - bordering Brazil - leprosy is still present and shows a tendency to recrudesce with about 10 new cases per year. Armadillo consumption is frequent.

Objectives: The main objective of the present study is the genotyping of M. leprae strains found in leprosy patients in French Guiana. The secondary objectives are to investigate the presence of M. lepromatosis in these patients, the molecular research of M. leprae resistance to anti-leprosy antibiotics, the study of risk factors for leprosy in humans in Guyana and in particular direct or indirect contact with armadillos, as well as the determination of phylogenetic links between the M. leprae strains found in French Guiana, and with the regional and world reference strains Population and methods: A cross-sectional study will be conducted on approximately 150 cases of leprosy diagnosed between 2006 and 2022 in French Guyana, seen by the department's anti-leprosy service and for which a skin biopsy (or dermal smear or nasal swab) is available. Genotyping of M. leprae and the search for antibiotic resistance, as well as the search for M. lepromatosis will be carried out by molecular biology. Human strains will be compared with environmental strains from French Guiana and with reference strains found in humans and armadillos. A minimum-spanning-tree and maximum parsimony analysis will be performed to determine the phylogenetic relationships between the different strains.

A 3:1 matched case-control study will be conducted to assess risk factors for leprosy in French Guiana. The 92 cases will be recruited from among leprosy cases diagnosed between 2006 and 2022 in French Guyana, seen by the departmental leprosy control. The 276 controls will be recruited by dermatologists from the Cayenne hospital, throughout the territory, by matching 3 controls per case according to sex and age (± 5 years). A standardised exposure questionnaire will be conducted face to face or by telephone. The search for leprosy risk factors and in particular direct or indirect contact with armadillos (proximity / hunting / handling / consumption) will be explored by univariate and then multivariate conditional logistic regressions taking into account known potential confounding factors.