Retrospective Review of Routine Mycobacterial Screening in a Captive Collection of Atlantic Bottlenose Dolphins (Tursiops truncatus)
Non-tuberculous mycobacteriosis has been reported in cetaceans.1-5 Normal results of acid-fast cytology and mycobacterial cultures from cetaceans are not well established and some have theorized that the aquatic environment may increase the risk of false positive test results. In 2004, an adult male Atlantic bottlenose dolphin (Tursiops truncatus) at the National Aquarium was evaluated for respiratory disease. Non-tuberculous mycobacteriosis was initially suspected when beaded, gram-positive rods were identified on diagnostic samples from respiratory secretions and gastric fluid. The bacteria appeared morphologically similar to non-tuberculous mycobacteria routinely identified in fish mycobacteriosis cases. Acid-fast stained cytology, culture/PCR testing, and histopathology subsequently supported a diagnosis of pulmonary Mycobacterium abscessus infection.3
Screening of fluid and tissue samples from the remaining population was instituted. Samples were collected during routine quarterly health exams or as part of diagnostic evaluations. All animals were managed in an indoor, artificial saltwater system with ozone disinfection.
Between October 1, 2004 and December 31, 2009, 913 acid-fast cytology and 74 mycobacterial culture samples were evaluated from 13 animals. Acid fast stained cytology samples were 99% negative (904/913) and 1% positive (9/913). Culture samples were 95.9% negative (71/74) and 4.1% positive (3/74). M. abscessus, M. aurum/neoaurum, and M. neoarum/lacticola were identified on positive cultures. Cytology and culture results were overwhelmingly negative for acid-fast positive organisms and mycobacteria. Positive results were sporadically identified, not repeatable, and primarily consistent with environmental contamination. Repeatable, positive results on either test are considered abnormal and additional follow-up would be warranted.
The authors would like to thank the Clinical Pathology Laboratory and Marine Mammal staff at the National Aquarium for their participation in this work.
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