Llana, M. | bioRxiv Science

bioRxiv2026

Continental-scale survey of Treponema pallidum in African nonhuman primates: expanding the range to the Mediterranean basin

Background: Treponema pallidum, the causative agent of yaws, bejel, and syphilis, is a significant pathogen affecting both humans and nonhuman primates (NHPs). While its presence is documented in several African NHP species, the continental-scale distribution, ecological drivers, and status in North African populations remain poorly understood. We conducted a large-scale, non-invasive survey to investigate the circulation of T. pallidum across African NHP populations and evaluate geographical and ecological patterns of exposure. Results: A total of 1,696 fecal samples from 11 wild NHP species collected across five African countries were screened for anti-T. pallidum antibodies using an automated chemiluminescent Simple Western assay, and fecal and dipteran samples were analyzed by molecular methods. Widespread seropositivity was observed across all African sites and multiple primate taxa, including great apes and cercopithecids. We provide the first evidence of T. pallidum antibodies in Barbary macaques (Macaca sylvanus) from North Africa, extending the known distribution of the pathogen to the Mediterranean basin. In West Africa, chimpanzees (Pan troglodytes verus) from Senegal and Guinea exhibited particularly high seroprevalence, confirming this region as a major endemic hotspot. In Central Africa, substantial circulation was documented in Cercopithecus wolfi, Cercopithecus ascanius, and western lowland gorillas (Gorilla gorilla gorilla). Arid/savanna biomes showed significantly higher exposure than Mediterranean and tropical rainforest biomes. No T. pallidum DNA was detected in fecal or dipteran samples. Conclusion: Our findings demonstrate widespread circulation of T. pallidum among African NHPs, reveal its presence in North African primate populations for the first time. The observed high seroprevalence, coupled with significant variations across species and geographical regions, suggests the existence of multiple transmission pathways adapted to specific host behaviors and environmental constraints. These results support the existence of a broad multihost sylvatic reservoir and provide new insights into the ecology of T. pallidum, with important implications for wildlife health, One Health surveillance, and yaws eradication efforts.

microbiology↗

bioRxiv2020

Chimpanzee (Pan troglodytes verus) density and environmental gradients at their biogeographical range edge

Identifying ecological gradients at the range edge of a species is an essential step in revealing the underlying mechanisms and constraints that limit the species geographic range. We aimed to describe the patterns of variation in chimpanzee (Pan troglodytes verus) density and habitat characteristics perpendicular to the northern edge of their range and to investigate potential environmental mechanisms underlying chimpanzee distribution in a savanna-mosaic habitat. We estimated chimpanzee densities at six sites forming a 126 km latitudinal gradient at the biogeographical range edge of the western chimpanzee in the savanna-mosaic habitats of southeastern Senegal. To accompany these data, we used systematically placed vegetation plots to characterize the habitats at each site for habitat heterogeneity, tree density and size, floral assemblages, among other variables. We found that both biotic and abiotic factors are potential determinants of the chimpanzee range limit in this ecoregion. Specifically, chimpanzee-occupied landscapes at the limit had smaller available floral assemblages, less habitat heterogeneity, and contained fewer closed canopy habitats in which chimpanzees could seek refuge from high temperatures than landscapes farther from the range limit. This pattern was accompanied by a decline in chimpanzee density with increasing proximity to the range limit. Our results provide several indications of the potential limits of food species diversity, thermal refuge, and water availability to the chimpanzee niche and the implications of these limits for chimpanzee biogeography, especially in the face of climate change predictions, as well as to species distributional modeling more generally.

ecology↗