Abstract

Humans are considered the main host for Mycobacterium leprae, the aetiologic agent of leprosy, but spill-over to other mammals such as nine-banded armadillos and red squirrels occurs. Although naturally acquired leprosy has also been described in captive nonhuman primates, the exact origins of infection remain unclear. Here, we report on leprosy-like lesions in two wild populations of western chimpanzees (Pan troglodytes verus) in the Cantanhez National Park, Guinea-Bissau, and the Tai National Park, Cote dIvoire, West Africa. Longitudinal monitoring of both populations revealed the progression of disease symptoms compatible with advanced leprosy. Screening of faecal and necropsy samples confirmed the presence of M. leprae as the causative agent at each site and phylogenomic comparisons with other strains from humans and other animals show that the chimpanzee strains belong to different and rare genotypes (4N/O and 2F). The independent evolutionary origin of M. leprae in two geographically distant populations of wild chimpanzees, with no prolonged direct contact with humans, suggests multiple introductions of M. leprae from an unknown animal or environmental source.