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.

Buruli ulcer is a necrotizing skin disease caused by Mycobacterium ulcerans and associated with exposure to aquatic habitats. To assess possible transmission of M. ulcerans by aquatic biting insects, we conducted a fi eld examination of biting water bugs (Hemiptera: Naucoridae, Belostomatidae, Nepidae) in 15 disease-endemic and 12 non-disease-endemic areas of Ghana, Africa. From collections of 22,832 invertebrates, we compared composition, abundance, and associated M. ulcerans positivity among sites. Biting hemipterans were rare and represented a small percentage (usually <2%) of invertebrate communities. No signifi cant differences were found in hemipteran abundance or pathogen positivity between disease-endemic and nondisease-endemic sites, and between abundance of biting hemipterans and M. ulcerans positivity. Therefore, although infection through insect bites is possible, little fi eld evidence supports the assumption that biting hemipterans are primary vectors of M. ulcerans. M ycobacterium ulcerans infection is an emerging skin disease often called Buruli ulcer (BU). Infection results in illness and lasting negative socioeconomic effects in rural areas of the tropics and subtropics (1). The pathologic changes, clinical signs and symptoms, and treatment have been reviewed elsewhere (2-5). In this article we evaluate fi eld evidence for the potential of aquatic invertebrates to be vectors of M. ulcerans.The exact mode of BU transmission remains unknown; however, past epidemiologic studies have associated BU with human activity near, or within, slow-fl owing or standing water bodies that have been created or disturbed by humans (2-4). Although several water-related risk factors have been recognized, none has been consistently reported, making it diffi cult to identify specifi c water-related risk activities (6-8). Most studies suggest that infection occurs through inoculation of M. ulcerans into skin lesions or insect bites (2,4,9-11). Portaels et al. (11) were the fi rst to propose that aquatic insects might serve as vectors of M. ulcerans. This hypothesis maintains that M. ulcerans is found in biofi lms of aquatic habitats and concentrated by grazing or fi lter-feeding invertebrates that are then consumed by predators known to bite humans (11). Initial evidence for this hypothesis used PCR detection of the insertion sequence IS2404 to document M. ulcerans' association with biting water bugs (Hemiptera), fi ltered concentrates of water, detritus, and aquatic plants (4,(12)(13)(14). These studies were important for understanding the possible environmental reservoirs of M. ulcerans. However, IS2404 is now understood to be not specifi c for M. ulcerans because this insertion sequence has been found in a number of other aquatic mycobacterial species, including M. marinum (15)(16)(17). When more discriminatory methods based on detection of variable number tandem repeats were used, many IS2404-positive environmental samples were reported to lack M. ulcerans (18). In light of these recent fi ndings, the relative fr...

Pathogens that use multiple host species are an increasing public health issue due to their complex transmission, which makes them difficult to mitigate. Here, we explore the possibility of using networks of ecological interactions among potential host species to identify the particular disease-source species to target to break down transmission of such pathogens. We fit a mathematical model on prevalence data of Mycobacterium ulcerans in western Africa and we show that removing the most abundant taxa for this category of pathogen is not an optimal strategy to decrease the transmission of the mycobacterium within aquatic ecosystems. On the contrary, we reveal that the removal of some taxa, especially Oligochaeta worms, can clearly reduce rates of pathogen transmission and should be considered as a keystone organism for its transmission because it leads to a substantial reduction in pathogen prevalence regardless of the network topology. Besides its potential application for the understanding of M. ulcerans ecology, we discuss about how networks of species interactions can modulate transmission of multi-host pathogens.

Numerous studies have associated Buruli ulcer (BU) disease with disturbed aquatic habitats; however, the natural reservoir, distribution, and transmission of the pathogen, Mycobacterium ulcerans, remain unknown. To better understand the role of aquatic plants in the ecology of this disease, a large-scale survey was conducted in waterbodies of variable flow throughout three regions of Ghana, Africa. Our objectives were to characterize plant communities and identify potential relationships with M. ulcerans and other mycolactone-producing mycobacteria (MPM). Waterbodies with M. ulcerans had significantly different aquatic plant communities, with submerged terrestrial plants identified as indicators of M. ulcerans presence. Mycobacterium ulcerans and MPM were detected on 14 plant taxa in emergent zones from both lotic and lentic waterbodies in endemic regions; however, M. ulcerans was not detected in the non-endemic Volta region. These findings support the hypothesis that plants provide substrate for M. ulcerans colonization and could act as potential indicators for disease risk. These findings also suggest that M. ulcerans is a widespread environmental bacteria species, but that it is absent or reduced in regions of low disease incidence. A better understanding is needed regarding the mechanistic associations among aquatic plants and M. ulcerans for identifying the mode of transmission of BU disease.