Distribution and prevalence of Sarcina troglodytae in chimpanzees and the environment throughout Africa

TL;DR

This study investigates the spread of a deadly bacterium in chimpanzees and their environments across Africa, finding it most common in one sanctuary linked to a fatal disease.

Contribution

The study provides the first comprehensive analysis of Sarcina troglodytae's distribution and environmental prevalence in chimpanzee populations across Africa.

Findings

S. troglodytae was most prevalent in chimpanzees and soil at the Sierra Leone sanctuary during the dry season.

The bacterium was absent in Congolese sanctuary and Sierra Leonean wild chimpanzee populations.

The Sarcina genus was widespread in all chimpanzee populations but more common in sanctuary animals.

Abstract

Introduction. Since 2005, the leading cause of death for western chimpanzees (Pan troglodytes verus) at Tacugama Chimpanzee Sanctuary (TCS) in Sierra Leone has been epizootic neurologic and gastroenteric syndrome (ENGS), associated with the bacterium Sarcina troglodytae (family Clostridiaceae).

Gap Statement. The prevalence of S. troglodytae at TCS in clinically normal chimpanzees and the environment remains unknown, as does its distribution in other captive and wild chimpanzee populations and their environments across Africa.

Aim. The aim of this study was to determine the distribution and prevalence of Sarcina bacteria in sanctuary and wild chimpanzee populations across Africa and to identify demographic and ecological risk factors for S. troglodytae in chimpanzees and the environment.

Methodology. We conducted a prospective, multi-season epidemiological investigation of S. troglodytae in chimpanzees and the environment at TCS and a parallel study at a sanctuary in the Republic of Congo. We also describe the results of surveys of chimpanzees at a sanctuary in Uganda and wild chimpanzee populations in Sierra Leone and Uganda for S. troglodytae. In total, we tested 637 chimpanzee and environmental samples using a species-specific PCR for S. troglodytae and a pan-Sarcina PCR.

Results.
S. troglodytae was more prevalent in chimpanzees at TCS (n=60) during the dry season (96.7%) than during the rainy season (55.2%). Soil was the most common environmental source of the bacterium (54% dry season vs. 4.8% rainy season). Notably, we did not detect S. troglodytae in faecal samples from sanctuary chimpanzees in the Republic of Congo (n=79) or in wild chimpanzees in Sierra Leone (n=18). We did detect the bacterium in East African chimpanzees (n=84) but at low prevalence (2.6%–10.9%). In contrast, we found the genus Sarcina to be ubiquitous in all chimpanzee populations with a higher prevalence in sanctuary chimpanzees (93.1%–100%) than in wild chimpanzees (66.7%–68.4%).

Conclusion.
S. troglodytae is markedly more prevalent at TCS, the only location affected by ENGS, than at any other location tested, and soil is a likely reservoir of S. troglodytae. These findings strengthen the association between S. troglodytae and ENGS and have implications for sanctuary management and conservation of western chimpanzees.

Figures