Buruli ulcer, caused by Mycobacterium ulcerans is a serious condition that seems to be increasing in several parts of Africa. It is also found in southeastern Australia. How the infection is transmitted is unclear, though it is generally believed that M. ulcerans is an aquatic pathogen and that humans are infected through contact with certain aquatic environments (swamps and slow-flowing water). But now Australian research  has suggested that wild mammals may play an important role.
The researchers collected a range of environmental samples from a small town endemic for the disease and from areas with few or no reported incident cases. M. ulcerans DNA was detected in soil, sediment, water residue, aquatic plant biofilm and terrestrial vegetation collected in the endemic area, with higher levels in the faeces of two species of possum than in other samples. (Possums are small arboreal marsupial mammals, native to Australia.)
Systematic testing of possum faeces detected M. ulcerans DNA in 41% of faecal samples collected in the endemic town, compared with less than 1% of faecal samples collected from non-endemic areas. Capture and clinical examination of live possums in the endemic area revealed that 38% and 24% of the two species respectively had laboratory-confirmed M. ulcerans skin lesions and/or M. ulcerans-positive faeces. Whole genome sequencing also revealed an extremely close genetic relationship between human and possum M. ulcerans isolates.
These findings raise the possibility that mammals are an environmental reservoir for Buruli ulcer infection but further research will be necessary, particularly in Africa. The Australian researchers note that there has been research in West Africa, which failed to detect M. ulcerans in the organs or faeces of rodents and shrews, but clearly the issue deserves further attention.
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