Aquatic Insects and Mycobacterium ulcerans: An Association Relevant to Buruli Ulcer Control?

M ycobacterium ulcerans infection, which can cause Buruli ulcer, is the third most common human mycobacteriosis worldwide, after tuberculosis and leprosy. Buruli ulcer occurs predominantly in humid tropical areas of Asia, Latin America, and, mainly, Africa, where the incidence has been increasing, surpassing tuberculosis and leprosy in some regions [1]. Buruli ulcer is a devastating, necrotizing, " skin-eating " disease of the poor, sometimes producing massive, disfi guring ulcers, with a huge social impact [1,2]. Furthermore, both Buruli ulcer and its pathogen have high scientifi c interest, with unique, enigmatic, and controversial features [1–4]. However, research on Buruli ulcer has been limited, although interest has grown since 1998, when the World Health Organization established the Global Buruli Ulcer Initiative, and in 2004 called for urgent action to control the disease and to increase research. There is no vaccine against Buruli ulcer and treatment remains diffi cult [1,2,5]. A detailed description of M. ulcerans infection, including its clinical aspects, is available at http:⁄⁄www.afi p.org/ Departments/infectious/bu/. A new area of research is the association between arthropods and M. ulcerans. And now a new study in PLoS Medicine, by Marsollier and colleagues, takes our understanding of this association further. There is evidence that M. ulcerans is not transmitted person-to-person but is an environmental pathogen transmitted to humans from its aquatic niches [6,7]. However, it is not clear how this transmission occurs [6,7]. Arthropods can be vectors of many infectious agents. The hypothesis that arthropods were involved in the transmission of M. leprae to humans was originally put forward at the end of the 19th century [8]. This hypothesis was intermittently considered and tested until the early 1990s, but it was never consistently demonstrated. The hypothesis that predatory aquatic insects, including those in the families Naucoridae and Belostomatidae (order Hemiptera) (Figure 1), were transmitters of M. ulcerans from aquatic niches to humans was advanced in 1999 [9]. The hypothesis was later reinforced by Marsollier and colleagues on the basis that [10]: (1) the salivary glands of Naucoris cimicoides are colonised with M. ulcerans upon feeding on grubs containing the pathogen; (2) M. ulcerans-infected N. cimicoides transmit the pathogen to mice upon biting; and (3) N. cimicoides in Buruli ulcer–endemic areas can be naturally colonised by M. ulcerans; this colonisation may occur through feeding on aquatic snails and fi sh, which take up M. ulcerans from water, mud, and aquatic plants [6,7]. These results have …