Mycobacteria infections are sporadically documented in wild sea turtles and are generally regarded as opportunistic pathogens. This case series describes infections by a Mycobacterium ulcerans ecovar in 2 imperiled species of sea turtle, the Kemp's ridley Lepidochelys kempii (n = 5) and loggerhead turtle Caretta caretta (n = 1). Most cases were stranded animals that presented with neurological abnormalities resulting from severe mycobacterial meningoencephalitis. In 4 instances, infected turtles were found in relative proximity to one another and without evident predisposing conditions, suggesting the potential for broader population health significance. Lesions were predominantly heterophilic and histiocytic, and were characterized by extensive leukocytic necrosis, absence of organized granuloma formation within the nervous system, fibrinoid vascular necrosis, and myriad extracellular and intrahistiocytic acid-fast bacilli. Except for one severely bacteremic animal, involvement of visceral organs was relatively mild and often paucibacterial. Multiple genetic loci were 100% identical in all 6 affected turtles and to multiple reported M. ulcerans ecovars; an ITS2 sequence amplified from each turtle was 100% identical only to M. pseudoshottsii, a pathogen of wild and farmed fish. The genetic relatedness of the organism to M. ulcerans ecovars known to produce mycolactones (polyketide toxins) suggests that the distinct pathological features among these cases are the result of a mycolactone-producing species of mycobacteria. This is the first report of M. ulcerans ecovar infection of a reptile. Mycobacterial meningoencephalitis should be considered as a differential etiological diagnosis for neurological disease in wild sea turtles.
Keywords: Mycobacteriosis; Mycobacterium pseudoshottsii; Mycobacterium ulcerans; Mycolactone; Nervous system; Sea turtle.