Environmental M. ulcerans linked to incidence of Buruli ulcer in Benin
MedWire News: Research carried out in Benin in West Africa shows that environmental Mycobacterium ulcerans predicts prevalence of Buruli ulcer, a necrotizing skin disease common in subtropical countries.
The investigators found that water and aquatic plant samples collected from villages with endemic Buruli ulcer tested positive for M. ulcerans, whereas those collected in areas with no previous cases of the disease did not.
Previous research has suggested that transmission of M. ulcerans is likely to come from the environment.
"There is a strong epidemiological association with residence near slow moving water, but lack of accurate case data in Africa has greatly complicated transmission studies of M. ulcerans from the environment to humans," explain Pamela Small (University of Tennessee, Knoxville, USA) and colleagues.
To investigate transmission further, the team collected water and aquatic plant samples from 22 villages in three areas of Benin. These included 12 villages within the Ouheme and Couffo River drainages with endemic Buruli ulcer and 10 villages near the Mono River and the coast or ridge with no prior reports of the disease.
The M. ulcerans genome sequence was completed in 2004 making accurate molecular identification of the bacteria easier. Small et al combined accurate environmental testing with Buruli case data from a well-established active surveillance program in Benin.
They found that samples taken from the environment of all 12 villages with endemic Buruli ulcer tested positive for M. ulcerans, but only one out of 10 villages with no prior history of the condition had samples that tested positive for the bacteria.
"Although results in this paper are consistent with results from many other studies reporting M. ulcerans DNA in natural water sources and water filtrand, our data do not support a role for transmission of M. ulcerans through direct contact with water or suggest that M. ulcerans grows freely in water," elaborate Small and co-workers.
"Our results are more consistent with the hypothesis that organisms detected in water are swept into aquatic sites through run-off from precipitation or sloughing from biofilms within the aquatic habitat."
The researchers say that their results raise the possibility that humans have a greater influence on the ecology of M. ulcerans than previously thought.
"Many environmental pathogens are widespread in the environment in the absence of human disease," they write in PLoS Neglected Tropical Diseases.
"The failure to obtain definitive proof for M. ulcerans in environmental samples where Buruli ulcer is absent raises the intriguing possibility that humans play a role in the distribution of M. ulcerans."
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By Helen Albert