Pathology of an unusual outbreak of fatal disease associated with mycobacterial and Pseudomonas aeruginosa infections and intracytoplasmic inclusion bodies in juvenile spectacled caimans (Caiman crocodilus)

The spectacled caiman (Caiman crocodilus) is a common crocodilian species used for exhibition in zoos and for luxury leather and meat production. We investigated unusual mortality among juvenile spectacled caimans in a zoo in Malaysia over a 2-year period. Clinical signs included inappetence, poor body condition, dehydration and ocular lesions. Necropsy findings included integumentary, respiratory and renal abnormalities. Histopathological analyses revealed necrotic plugs and intracytoplasmic eosinophilic inclusion bodies in epidermal keratinocytes, granulomatous lesions in the lungs and liver and gout crystals in the kidneys. Acid-fast, beaded, rod-shaped bacteria were identified in the granulomatous lesions using Ziehl–Neelsen staining. Microbiological investigations identified Pseudomonas aeruginosa as the predominant pathogen, while mycobacteriosis was also detected and poxvirus infection was suspected. However, due to the lack of suitable samples, molecular diagnosis was challenging. These findings emphasize the multifactorial nature of disease in captive spectacled caimans and the need for enhanced management strategies to mitigate health risks and preserve population viability.