Mycolactone-producing Mycobacterium marinum infection in captive Hong Kong warty newts and pathological evidence of impaired host immune function.
A mass mortality event of captive Hong Kong warty newts Paramesotriton hongkongensis with non-granulomatous necrotic lesions occurred in Taipei Zoo, Taiwan, in 2014. Clinically, the sick newts were lethargic and often covered with water mold Saprolegnia sp. on the skin of the body trunk or extremities. Predominant pathological findings were multifocal non-granulomatous necrotic lesions in the liver, spleen, and kidneys and severe skin infection with Saprolegnia sp., with deep invasion and involvement of underlying muscles. The possibility of ranavirus infection was ruled out by negative PCR results. Unexpectedly, abundant intralesional acid-fast positive bacilli were found in the necrotic lesions of the liver, spleen, and kidney in all 14 sick newts. PCR targeting the hsp65, ITS region, and partial 16S rRNA genes was performed, and the sequence identity from amplified amplicons of hsp65 and partial 16S rRNA genes was 100% identical to that of the corresponding gene fragment of Mycobacterium marinum. Further molecular investigations demonstrated that the current M. marinum was a mycolactone-producing mycobacterium with the presence of esxA/esxB genes. Mycolactone is a plasmid-encoded, immunosuppressive, and cytotoxic toxin. The possible immunosuppression phenomenon characterized by systemic non-granulomatous necrotic lesions caused by M. marinum and the unusual deep invasive infection caused by water mold might be associated with the immunosuppressive effect of mycolactone. Therefore, it should be noted that non-granulomatous necrotic lesions in amphibians can be caused not only by ranavirus infection but also by mycobacteriosis.
Graduate Institute of Molecular and Comparative Pathobiology, School of Veterinary Medicine, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan.
Wen-Ta
WT
Li
Hui-Wen
HW
Chang
Victor Fei
VF
Pang
Fun-In
FI
Wang
Chen-Hsuan
CH
Liu
Ting-Yu
TY
Chen
Jun-Cheng
JC
Guo
Takayuki
T
Wada
Chian-Ren
CR
Jeng
D000818:Animals; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D018942:Macrolides / Q000378:metabolism*; D009165:Mycobacterium Infections, Nontuberculous / Q000276:immunology / Q000382:microbiology / Q000401:mortality / Q000662:veterinary*; D019910:Mycobacterium marinum / Q000235:genetics / Q000378:metabolism*; D012455:Salamandridae / Q000276:immunology / Q000382:microbiology*
D004269:DNA, Bacterial; D018942:Macrolides; C117218:mycolactone
Hong Kong warty newt; Mycobacterium marinum; Mycolactone; Saprolegnia sp.