Domestic animals infected with Mycobacterium ulcerans—Implications for transmission to humans

BackgroundThe environmental pathogen, Mycobacterium ulcerans (MU) can infect both humans and animals and cause Buruli ulcer (BU) disease. However, its mode(s) of transmission from the colonized environment to human/animal hosts remain unclear. In Australia, MU can infect both wildlife and domestic mammals. Till date, BU-like lesions have only been reported in wildlife in Africa. This warrants a thorough assessment of possible MU in domestic animals in Africa. Here, we screened roaming domesticated animals that share the human microhabitat in two different BU endemic sites, Sedje-Denou in Benin and Akonolinga in Cameroon, for MU lesions.Methodology/Principal findingsWe screened roaming mammals and birds across 3 endemic villages of Sedje-Denou in Southern Benin and 6 endemic villages of Akonolinga in Cameroon. After approval from relevant authorities, specimens (wound swabs and tissue fragments) were collected from animals with open or active lesion and systematically screened to detect the presence of MU though the diagnostic DNA targets IS2404, IS2606 and KR-B. Out of 397 animals surveyed in Akonolinga, 44 (11.08%) carried skin lesions and all were negative for MU DNA. For Sedje-Denou, only 25 (6.93%) out of 361 animals surveyed carried external skin lesions of which 2 (8%) were positive for MU DNA targets. These MU infected lesions were found in two different villages on a goat (abdominal part) and on a dog (nape area of the neck). Source-tracking of MU isolates within infected animal lesions was performed using VNTR genotyping and further confirmed with sequencing. One MU VNTR genotype (Z) was successfully typed from the goat lesion. The evolutionary history inferred from sequenced data revealed a clustering of animal MU isolates within isolates from human lesions.Conclusion/SignificanceThis study describes the first report of two MU infected lesions in domestic animals in Africa. Their DNA sequence analyses show close relationship to isolates from human cases. It suggests that MU infection should be suspected in domestic hosts and these could play a role in transmission. The findings further support the hypothesis that MU is a ubiquitous environmental pathogen found in endemic areas, and probably involved in a multiple transmission pathway.研究背景 环境病原体溃疡分枝杆菌（Mycobacterium ulcerans, MU）可感染人类与动物，引发布鲁里溃疡（Buruli ulcer, BU）疾病。然而，该菌从定植环境传播至人类或动物宿主的具体途径仍不明确。在澳大利亚，MU可感染野生哺乳动物与家养哺乳动物。截至目前，非洲地区仅在野生动物中报道过类布鲁里溃疡病变。因此有必要对非洲家养动物中的MU感染情况开展全面评估。本研究针对贝宁塞杰-德努（Sedje-Denou）与喀麦隆阿科诺林加（Akonolinga）两处布鲁里溃疡流行区域中，与人类共享微生境的漫游家养动物，开展MU感染病变筛查。 研究方法与主要结果 我们在贝宁南部塞杰-德努的3个流行村庄与喀麦隆阿科诺林加的6个流行村庄中，对漫游的哺乳动物与鸟类进行了筛查。经相关主管部门批准后，从出现开放性或活动性病变的动物身上采集样本（伤口拭子与组织碎片），并通过靶向诊断DNA序列IS2404、IS2606与KR-B，系统筛查样本中是否存在MU。阿科诺林加地区共调查397只动物，其中44只（11.08%）存在皮肤病变，且所有病变样本的MU DNA检测均为阴性。塞杰-德努地区共调查361只动物，仅25只（6.93%）存在体表皮肤病变，其中2只（8%）的MU DNA靶向检测结果为阳性。这两例MU阳性病变分别来自两个不同村庄的一只山羊（腹部部位）与一只犬（颈背区域）。通过可变数目串联重复序列基因分型（Variable Number Tandem Repeat genotyping, VNTR genotyping）对感染动物病变中的MU分离株进行溯源，并通过测序进一步验证。从山羊病变样本中成功分型得到一种MU VNTR基因型（Z）。基于测序数据的进化分析显示，动物来源的MU分离株与人类病例来源的MU分离株聚为一支。 结论与研究意义 本研究首次报道了非洲家养动物中的两例MU感染病变。DNA序列分析显示，这些分离株与人类病例的分离株亲缘关系密切。该结果提示，家养宿主中也应警惕MU感染，且家养动物可能在MU传播中发挥一定作用。本研究结果进一步支持以下假说：MU是流行区域中广泛存在的环境病原体，且可能通过多种途径进行传播。