Anthropogenic activity has endangered the survival of sea turtle populations worldwide. Commercial fishing, coastal development, climate change, and pollution continue to be predominant threats for sea turtles. To maintain population sizes, marine animal rehabilitation centers rescue and rehabilitate sick and injured sea turtles. This has allowed researchers to better understand the illnesses and infections encountered by turtles in the wild. Osteomyelitis is one of these diseases whose presence in sea turtles has allowed rehabilitators to improve their treatment strategies.
Osteomyelitis is direct infection of the bone and was originally described in humans and mammals. It was first found in reptiles in 1981 when a stranded leatherback turtle presented evidence of osteolysis, or bone resorption, in its elbow joint. The surrounding bones and cartilage were demineralized and replaced by tissue that allowed for a minimal range of motion (Ogden et al. 1981). Osteomyelitis has been found to appear either as an area of osteolytic bone degeneration or as an area of new and unstable bone formation (Rothschild et al. 2013). The bacteria that infect the bone are most commonly gram-negative. They usually arise from a focal point somewhere else in the body, such as an external wound or the intestines (Ogden et al. 1981). While some of the bacteria that invoke osteomyelitis are of foreign origin, most can be found in healthy turtles’ mouth, skin, and digestive system (Innis et al. 2014).
The most prominent cause of osteomyelitis is immunosuppression during cold-stunning. When sea turtles are cold-stunned, their bodies slowly shut down, compromising their immune system (Guthrie et al. 2010). Cold-stunned turtles are also more likely to experience traumatic injuries and inhale water, allowing bacteria to enter the bloodstream. With a compromised immune system, turtles are unable to fight off bacterial infection, allowing for the hematogenous spread of bacteria throughout the body and infecting the bones (Pace et al. 2018). However, recent evidence has suggested that some cases of osteomyelitis may have actually started while the turtles were in captivity (Cruciani et al. 2019). Bringing in cold-stunned sea turtles for rehabilitation can be risky if the turtle exhibits external penetrating wounds. These integumentary openings provide a perfect entry for bacteria from other turtles, posing a risk for infection (Harms et al., 2003). Furthermore, the immune suppression of turtles in captivity may not only be related to cold stunning. Frequent handling of turtles can cause mechanical stress and joint inflammation. The stress associated with rehabilitation can weaken a turtle’s immune system and make it more susceptible to bacterial or fungal infection. Captivity induced immunosuppression is believed to have been the source of osteomyelitis in at least nine sea turtles at a rehabilitation center in France (Cruciani et al. 2019).
Most of the severe bacterial infections that cause osteomyelitis are from gram-negative bacteria. The antibiotic-resistant nature of this bacteria can make the disease difficult to treat (Innis et al. 2014). Broad-spectrum antibiotics and antifungal medications were found to be effective in treating osteomyelitic lesions. Osteolytic regions had regained significant bone density only after treatments that lasted longer than three months (Cruciani et al. 2019). Treatment could be improved with a better understanding of the infection and risk factors that make sea turtles more susceptible to osteomyelitis. It is presumed that juvenile sea turtles with actively growing bones are more vulnerable to developing osteomyelitic lesions. However, this hypothesis is difficult to prove due to selection bias. For example, at a rehabilitation center currently participating in osteomyelitis research, only 2% of stranded turtles admitted to the center were adults (Cruciani et al. 2019).
Osteomyelitis can be a fatal infection, and understanding its origin can improve future treatments of sea turtles. The infection that causes osteomyelitis is often produced by bacteria and fungi healthy turtles encounter in the wild every day. However, immunosuppression related to cold-stunning or stress in captivity makes it hard for turtles to fight off any bacteria. This is especially important to keep in mind when handling sea turtles during rehabilitation procedures and when external wounds are present. With more research, treatments for osteomyelitis will hopefully become more consistent and effective at facilitating proper bone regeneration.
Cruciani, B., Shneider, F., Ciccione, S., Barret, M., Arné, P., Boulouis, H. J., & Vergneau-Grosset, C. (2019). Management of Polyarthritis Affecting Sea Turtles at Kélonia, the Reunion Island Sea Turtle Observatory (2013–17). Journal of wildlife diseases.
Guthrie, A., George, J., & deMaar, T. W. (2010). Bilateral chronic shoulder infections in an adult green sea turtle (Chelonia mydas). Journal of Herpetological Medicine and Surgery, 20(4), 105-108.
Harms, C. A., Lewbart, G. A., & Beasley, J. (2002). Medical management of mixed nocardial and unidentified fungal osteomyelitis in a Kemp’s ridley sea turtle, Lepidochelys kempii. Journal of Herpetological Medicine and Surgery, 12(3), 21-26.
Innis, C. J., Braverman, H., Cavin, J. M., Ceresia, M. L., Baden, L. R., Kuhn, D. M., … & Stacy, B. (2014). Diagnosis and management of Enterococcus spp infections during rehabilitation of cold-stunned Kemp’s ridley turtles (Lepidochelys kempii): 50 cases (2006–2012). Journal of the American Veterinary Medical Association, 245(3), 315-323.
Ogden, J. A., Rhodin, A. G., Conlogue, G. J., & Light, T. R. (1981). Pathobiology of septic arthritis and contiguous osteomyelitis in a leatherback turtle (Dermochelys coriacea). Journal of Wildlife Diseases, 17(2), 277-287.
Pace, A., Meomartino, L., Affuso, A., Mennonna, G., Hochscheid, S., & Dipineto, L. (2018). Aeromonas induced polyostotic osteomyelitis in a juvenile loggerhead sea turtle Caretta caretta. Diseases of Aquatic Organisms, 132(1), 79-84.
Rothschild, B. M., Schultze, H. P., & Pellegrini, R. (2013). Osseous and other hard tissue pathologies in turtles and abnormalities of mineral deposition. Morphology and evolution of turtles (pp. 501-534). Springer, Dordrecht.
Research review paper written by summer intern, Meaghan K. Meaghan is a student at Colgate University studying Marine and Freshwater Science.