A Case of Degenerative Joint Disease and Mycobacteriosis in a Kemp's Ridley Sea Turtle (Lepidochelys kempii)
This is an on-going case of chronic degenerative joint disease and mycobacteriosis in a 10+-year-old Kemp's Ridley sea turtle (Lepidochelys kempii) at a public aquarium. This animal initially presented as a stranded, cold-stunned, sea turtle in November, 2000, with signs of severe hypothermia (1°C), dehydration, bradycardia, bradypnea, lethargy, and frostbite. Due to pathologic lung changes, chronic anemia, and degenerative bone and joint disease, the animal was deemed unreleasable in August, 2001. Since then, it has been kept as an exhibit animal. The most striking feature of this turtle's clinical condition has been progressive degenerative joint disease involving the shoulder joints. This deterioration of the joints has resulted in reduced range of motion and decreased use of the front flippers. In 2005, imaging studies, including computed tomography, ultrasonography and nuclear scintigraphy revealed multiple fluid-filled masses surrounding the shoulders. Between 2000 and 2007, multiple bacterial and fungal cultures, cytologic samples, and biopsies were collected from a variety of tissues including these masses, the skin, carapace, blood, oral ulcers, feces, external wounds, and tracheal wash fluid. In 2005, histopathologic examination of a biopsy sample from the capsule of a mass revealed granulomas within dense collagenous connective tissue. In 2007, Mycobacterium chelonae was cultured from fluid obtained from these peri-articular lesions. To date, this mycobacterium has not been isolated from any other tissue. Mycobacterial infection was confirmed by histopathologic examination of the lesions in 2008. Complete blood counts and serum chemistry profiles have thus far shown changes associated with chronic disease, such as hyperglobulinemia and chronic anemia. More recently, the peri-articular lesions have increased in size, can be easily palpated, and have become more visibly prominent. The latest CT scan in October 2008 showed severe bilateral erosion of articular cartilage and subchondral bone lysis in the proximal humerus, scapula, and coracoid with degenerative changes and osteophyte formation. The peri-articular lesions have become more mineralized, less fluid-filled, and their fibrous capsules have thickened around the shoulders and the right anterior plastron. As a result, lung tissues are now displaced more caudally and dorsally than in the past. In light of the increased mineralization and deposition of scar tissue around the shoulders, the animal is expected to have increasingly reduced range of motion at both shoulder joints with time. Following consultations with reptile veterinarians and medical infectious disease specialists, treatment with triple antibiotic therapy consisting of clarithromycin, doxycycline and ciprofloxacin was started in February 2008. However, the most recent culture and histopathologic examination of the peri-articular tissue (October 2008) showed persistence of mycobacterial infection. It is not clear how the animal was originally infected. In general, it is thought that atypical mycobacterial infections are acquired from the environment, particularly when animals are immunocompromised. The water in this animal's exhibit is natural sea water from Boston Harbor, which could provide an environmental source of mycobacteria. Euthanasia has been considered for humane reasons, concerns over development of antibiotic resistance, and human and animal safety. However, at this time, the turtle continues to have a good appetite, is active, and is a popular exhibit animal. The risk that this animal may pose to humans and other animals is open to conjecture.
The authors wish to thank the Giant Ocean Tank divers and the Rescue and Rehabilitation Department at New England Aquarium for their support, and for the information they have provided for the current paper. We also thank the many veterinarians and physicians that have helped with this case, especially Drs. Salvatore Frasca Jr., Nadia Stegeman, Lindsey Baden and Duncan Kuhn.