Abstract
The last 20 years has seen a significant series of outbreaks of Buruli/Bairnsdale Ulcer (BU), caused by Mycobacterium ulcerans, in temperate south-eastern Australia (state of Victoria). Here, the prevailing view of M. ulcerans as an aquatic pathogen has been questioned by recent research identifying native wildlife as potential terrestrial reservoirs of infection; specifically, tree-dwelling common ringtail and brushtail possums. In that previous work, sampling of environmental possum faeces detected a high prevalence of M. ulcerans DNA in established endemic areas for human BU on the Bellarine Peninsula, compared with non-endemic areas. Here, we report research from an emergent BU focus recently identified on the Mornington Peninsula, confirming associations between human BU and the presence of the aetiological agent in possum faeces, detected by real-time PCR targeting M. ulcerans IS2404, IS2606 and KR. Mycobacterium ulcerans DNA was detected in 20/216 (9.3%) ground collected ringtail possum faecal samples and 4/6 (66.6%) brushtail possum faecal samples. The distribution of the PCR positive possum faecal samples and human BU cases was highly focal: there was a significant non-random cluster of 16 M. ulcerans positive possum faecal sample points detected by spatial scan statistics (P<0.0001) within a circle of radius 0.42 km, within which were located the addresses of 6/12 human cases reported from the area to date; moreover, the highest sample PCR signal strength (equivalent to ≥106 organisms per gram of faeces) was found in a sample point located within this cluster radius. Corresponding faecal samples collected from closely adjacent BU-free areas were predominantly negative. Possums may be useful sentinels to predict endemic spread of human BU in Victoria, for public health planning. Further research is needed to establish whether spatial associations represent evidence of direct or indirect transmission between possums and humans, and the mechanism by which this may occur.
Highlights
Mycobacterium ulcerans is an environmental, potentially zoonotic bacterial pathogen, which in humans causes the progressive ulcerative skin condition Buruli Ulcer (BU), a neglected tropical disease which is endemic in at least 30 countries worldwide [1]
We reported the detection of M. ulcerans DNA in the faeces of possums in an area of South-East Australia where the largest recorded outbreak of human BU has been in progress for the last decade
The current study was carried out in a new outbreak area, and describes the detection of M. ulcerans DNA in possum faeces collected from the ground, in locations which correspond closely with the addresses of human BU cases
Summary
Mycobacterium ulcerans is an environmental, potentially zoonotic bacterial pathogen, which in humans causes the progressive ulcerative skin condition Buruli Ulcer (BU), a neglected tropical disease which is endemic in at least 30 countries worldwide [1]. In south-east Australia, infection is consistently associated with coastal areas [8,9] and the mechanism of transmission remains elusive, several studies have indicated that mosquitoes may have a role [2,10]. An extensive survey conducted in an area endemic for human BU on the Bellarine Peninsula (Point Lonsdale; see map, Figure 1) revealed that a large proportion of faecal samples from common ringtail (Pseudocheirus peregrinus) and common brushtail (Trichosurus vulpecula) possums contained high concentrations of M. ulcerans DNA [16]. That study showed a strong association between BU endemicity of an area and the proportion and DNA concentration of M. ulcerans positive possum faecal samples.
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