Distribution of Mycobacterium ulcerans in Buruli Ulcer Endemic and Non-Endemic Aquatic Sites in Ghana

Abstract

Mycobacterium ulcerans, the causative agent of Buruli ulcer, is an emerging environmental bacterium in Australia and West Africa. The primary risk factor associated with Buruli ulcer is proximity to slow moving water. Environmental constraints for disease are shown by the absence of infection in arid regions of infected countries. A particularly mysterious aspect of Buruli ulcer is the fact that endemic and non-endemic villages may be only a few kilometers apart within the same watershed. Recent studies suggest that aquatic invertebrate species may serve as reservoirs for M. ulcerans, although transmission pathways remain unknown. Systematic studies of the distribution of M. ulcerans in the environment using standard ecological methods have not been reported. Here we present results from the first study based on random sampling of endemic and non-endemic sites. In this study PCR-based methods, along with biofilm collections, have been used to map the presence of M. ulcerans within 26 aquatic sites in Ghana. Results suggest that M. ulcerans is present in both endemic and non-endemic sites and that variable number tandem repeat (VNTR) profiling can be used to follow chains of transmission from the environment to humans. Our results suggesting that the distribution of M. ulcerans is far broader than the distribution of human disease is characteristic of environmental pathogens. These findings imply that focal demography, along with patterns of human water contact, may play a major role in transmission of Buruli ulcer.

Author Summary

Buruli ulcer is an ulcerative skin disease caused by Mycobacterium ulcerans. Though usually not fatal, ulceration can cover up to 15% of the body, with treatment being costly and sometimes painful. Primary risk for Buruli ulcer in Africa is exposure to stagnant water, but the route of transmission is unknown. Detection of M. ulcerans in aquatic insects in endemic sites suggests the presence of aquatic reservoirs. This article reports results from the first investigation into the ecology of M. ulcerans based on random sampling of both endemic and non-endemic aquatic sites. Development of a method for discriminating M. ulcerans from closely related mycobacterial pathogens made it possible to determine the distribution of M. ulcerans in aquatic environments. This article demonstrates the presence of M. ulcerans DNA in both endemic and non-endemic sites within aquatic insects, water filtrate, and glass-slide biofilm communities. This article provides data suggesting that M. ulcerans is more broadly distributed than the human disease it causes. This study provides an initial step for future work on whether certain M. ulcerans strains are particularly successful human pathogens and suggests that research on specific human water contact factors may provide insight into the transmission of M. ulcerans.