Author(s): Yuqian Luo aff1 , Yang Degang aff1 , Mikio Ohtsuka aff2 , Yuko Ishido aff1 , Norihisa Ishii aff1 , Koichi Suzuki [*] aff1
aquatic environment; Buruli ulcer; crayfish; familial concurrent occurrence of BU in Japan; Mycobacterium ulcerans subsp. shinshuense ; vector
Buruli ulcer (BU) is a severe emerging infectious skin disease caused by the pathogen Mycobacterium ulcerans . M. ulcerans primarily invades the skin, subcutaneous fat and fascia where production and secretion of the bacterial toxin mycolactone suppresses immune responses, eventually resulting in a focus of necrotic fat cells. Clinical manifestation of BU is characterized by a painless nodule with an enlarging central skin ulceration on exposed areas [1 ].
BU occurs in well-defined areas throughout the world, most frequently in tropical and subtropical areas. It is especially prevalent in African countries, with some countries having foci of disease occurrence. Currently, more than 5000 new cases are annually reported from countries in Africa, South America and Western Pacific regions [1 ]. Since 1982, a total of 32 cases have been reported in Japan, with indications of a steady increase in incidence since 2004 [2 ]. All cases in Japan are considered to have been domestic infections, since none of the patients had a history of overseas travel prior to onset. A new subspecies of M. ulcerans (M. ulcerans subsp. shinshuense ) is thought to be endogenous to Asia in general or Japan in particular. It was isolated and identified in 23 of the 32 Japanese cases based on homology to the 16S ribosomal RNA gene and the presence of the unique insertion sequence 2404 (IS2404 ) [3 ].
Most cases of BU are found in people living in or around aquatic environments (such as wetlands, rivers and reservoirs) [4-6 ], and detection of M. ulcerans from aquatic environments has been extensively reported in endemic countries [1 ]. Thus, although a possible disease vector or mode of transmission has not yet been conclusively established [4-6 ], it is believed that a strong association exists between BU and contaminated aquatic environments. Case-control studies conducted in BU-endemic countries and regions support the prevailing hypotheses that M. ulcerans is acquired from direct or indirect (via potential insect vectors) contact with aquatic environments that harbor the pathogen through penetrating skin injuries [7-9 ]. However, Japan has a climate that is distinct from that of the tropical or subtropical countries where BU is endemic. Therefore, the vector(s) and mode of transmission of M. ulcerans subsp. shinshuense in Japan may also differ from those in more highly endemic areas. In contrast to endemic areas, neither history of suspicious contact with an aquatic environment before symptom onset nor detection of the pathogenic organism in an aquatic environment had ever been reported in BU cases in Japan [3 ].
Recently, a rare case of familial concurrent occurrence of BU was reported in Fukushima Prefecture in Japan [10 ]. In November 2010, the family of a 2‐year-old girl observed a gradually enlarging eruption on her right cheek. At her first medical examination in December...