[Scientific news IRD]
Buruli ulcer is a serious skin disease caused by a bacterium from the same family as those that cause leprosy and tuberculosis. It is particularly prevalent in Africa, but also in South America, where the pathogen has just been identified in the natural environment for the first time.
This study, conducted in French Guiana by researchers members of the CEBA (IRD, Centre Hospitalier de Cayenne) in partnership with other organisms, sheds light on how the disease is transmitted and in what situations it is likely to emerge, something we still know little about.
Two laboratories of the CEBA contributed to this publication: Mivegec and EPAT.
Among the authors of the publication, we find Aaron Morris (Mivegec/University of Bournemouth, first author, PhD student whose thesis is supported by the CEBA), Pierre Couppié (Epat), Rodolphe Gozlan, Daniel Sanhueza, Rolland Ruffiné and Jean-François Guégan (Mivegec), all members of the CEBA.
What is Buruli ulcer?
Buruli ulcer is an emerging human skin disease found in more than 33 countries of tropical and subtropical regions, mainly in Africa. Each year, 15 of these 33 countries register 5000 to 6000 cases.
In 2010 in French Guiana, 7 new cases of infection were registered, in relation with the very low population density.
This infection is a necrosis of the skin and causes important ulceration, sometimes leading to permanent disability and social exclusion. Surgery has been the principal treatment of this disease for a long time.
Since 2004, antibiotic use has significantly improved the quality of care of the patients, who get tested earlier.
Bacterium detected in stagnant water
Cases of Buruli ulcer have been reported in Latin America since the late 1960s, the majority of them in French Guiana. However, until now, the bacterium responsible, Mycobacterium ulcerans, had never been observed in the environment in South America.
In order to identify where in the environment this micro-organism thrives and understand exactly how it infects humans, the research team analysed 23 natural freshwater sites along the coast of French Guiana, where human cases have been observed.
The researchers analysed a total of 174 samples from the water and various substrates of temporary or more permanent ponds and pools for M. ulcerans DNA.
Results: fourteen sites tested positive, five of them unequivocally so.
Watercourses: a source of contamination
More specifically, the study highlights the predominant role of hydrological factors in peaks in the disease among humans. During rainy periods, contaminated stagnant water upstream of the river basin is carried downstream into the coastal area, where a concentration of the bacterium is then found. In this scenario, the bacterium could come from the soil or be associated with plant root systems.
The Sinnamary River, located in the center of French Guiana, is a regular source of infection. However, the researchers have observed a significant reduction in the number of cases downstream of the river basin since the construction of the Petit-Saut hydroelectric dam in the 1990s.
Assessing risk of emergence
At present, our understanding of the disease in limited. The sources and modes of infection, as well as the interactions between the bacterium and its natural environment, remain to be clarified. Today, infection through direct contact with the skin would appear to be very unlikely. Transmission of the bacterium to humans by water bugs seems to be one possible means of transmission, but confirmation is required. The new study makes it easier to understand the spatial distribution of the bacterial agent in the environment. The researchers are now developing techniques for large-scale detection of M. ulcerans DNA, using new biomolecular tools.
This work will make it possible to assess the risk of Buruli Ulcer emerging in French Guiana and in Latin America as a whole, and, eventually, to reduce human contact with the pathogen by taking infection risk into account in development and urban planning projects. This study in French Guiana is being compared with similar work done in Cameroon and Benin.
Link to the IRD scientific news number 451 (in French) : http://www.ird.fr/la-mediatheque/fiches-d-actualite-scientifique/451-ulcere-de-buruli-la-bacterie-detectee-en-amerique-du-sud
Reference of the publication:
First Detection of Mycobacterium ulcerans DNA in Environmental Samples from South America
Aaron Morris, Rodolphe Gozlan, Estelle Marion, Laurent Marsollier, Demetra Andreou, Daniel Sanhueza, Rolland Ruffine, Pierre Couppié et Jean-François Guégan.
Review Plos Neglected Tropical Diseases, January 30th 2014.
To access the publication: http://www.plosntds.org/article/info%3Adoi%2F10.1371%2Fjournal.pntd.0002660
Rodolphe Gozlan, IRD researcher and member of the CEBA, email@example.com
Aaron Morris, PhD student at Mivegec and at the University of Bournemouth, firstname.lastname@example.org
Claire Lafleur, CEBA communication, email@example.com, tel : +594 (0)5 94 38 87 58