Mycolactone-producing Mycobacterium marinum infection in captive Hong Kong warty newts and pathological evidence of impaired host immune function

Abstract

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 nongranulomatous necrotic lesions in the liver, spleen, and kidneys and severe skin infection with Sapro legnia 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 myco bacterium 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.KEY WORDS: Hong Kong warty newt · Mycobacterium marinum · Mycolactone · Saprolegnia sp. Resale or republication not permitted without written consent of the publisherDis Aquat Org 123: [239][240][241][242][243][244][245][246][247][248][249] 2017 al. 2011). At least 72 amphibian species in 14 families are known to have been infected by ranaviruses, and host susceptibility varies among species and developmental stages (Miller et al. 2011). The histopathological lesions caused by ranaviruses are multifocal hemorrhagic and necrotic foci in multiple internal organs, and the renal tubular epithelium is also considered as one of the primary targets (Robert et al. 2005, Gray et al. 2009, Miller et al. 2011. Batrachochytrium dendrobatidis is the cau sative agent of chytridiomycosis, a potentially fatal epidermal infection in amphibians (Van Rooij et al. 2015). Recently, a new species of Batrachochytrium sp., named B. salamandrivorans, was discovered (Martel et al. 2014). This species, which most likely originated in Asia, is highly pathogenic to salamanders (Martel et al. 2014).Infectious diseases in amphibians such as mycobacteriosis, do not only affect ectothermic vertebrates, but can also cause disease in mammals, including humans (Densmore & Green 2007). Therefore, the zoonotic potential of some infectious diseases in amphibians and in exotic companion animals should not be overl...

Mycobacterium ulcerans and Mycobacterium marinum: Pathogenesis, Diagnosis and Treatment

“…Both M. marinum and M. ulcerans are known to be the two opportunistic mycobacterial pathogens, also named as the mycolactone-producing mycobacteria (MPM), that secrete plasmid-encoded mycolactone exotoxins [5] . Mycolactone is a cytotoxic polyketide metabolite produced by MPM, essential for bacterial virulence, to induce Buruli ulcer-like lesions characterized by extensive necrosis and void of inflammation in intradermal administered animal models [6] .…”