[Buruli ulcer: hypothetical modes of transmission of Mycobacterium ulcerans]

The incidence of Buruli ulcer, caused by Mycobacterium ulcerans, has been increasingly rapidly over the past thirty years, particularly in Africa. These extensive necrotic lesions are due to mycolactone, a toxin produced by the bacterium. The mode of Mycobacterium ulcerans transmission is still controversial, and several insect species have been incriminated. Several infected mosquito species have been identified in Australia, while predatory water bugs, particularly belostomatids and naucorids, have been implicated in Africa. Indeed, the bacterium has been detected in these insects' salivary glands, and experimental transmission to mice has been demonstrated, raising the possibility of human transmission by water bug bites. Interestingly, individuals highly exposed to water bug bites tend to be less often infected, indicating that frequent bites by non infected bugs might have a protective effect. Insect-borne transmission would be a minor route of transmission compared to direct transmission via skin trauma.