Potential Cofactors in the Recrudescence of Fibropapillomas in Rehabilitating Green Turtles (Chelonia mydas)
Chronic stress and immune system compromise have been implicated as potential contributors to an animal's poor health response in rehabilitation facilities. This presentation evaluates typical hematologic parameters used for health assessment and examines environmental factors and behavioral abnormalities that may influence the recrudescence of fibropapillomatosis (FP) in juvenile green sea turtles at the Clearwater Marine Aquarium during rehabilitation.
Fibropapillomatosis, a neoplastic disease that has been associated with a herpesvirus, affects numerous wild green sea turtle populations (Chelonia mydas) around the globe.3 A great deal of research has been directed at determining the etiology of this disease.4,5 Fibropapillomatosis is visually diagnosed by the presence of external fibroepithelial tumor bodies. It is usually associated with the soft tissues aspects of the body (integument, conjunctiva), though it has been seen on the carapace and plastron as well. The current therapeutic approach is surgical removal of the external tumors with a laser. Additional diagnostic techniques such as radiography, CT or MRI are utilized to determine the presence of internal tumors which are currently not treated, and are fatal. While FP may be present in different age classes, it is often the young juvenile turtles (30-50 cm straight carapace length) that are more likely to show recrudescence of the tumors after surgical removal.
Juvenile green turtles often show abnormal behavior patterns in captive situations. These include constant swimming and frenzied activity. Turtles may be found continuously at the surface of the pools exhibiting "spy-hopping" behavior and swimming back and forth along the pool wall. Many of these behaviors are escape mechanisms for small turtles likely to be predated upon in the wild. These activities may increase repetitive contact with projections in the environment, leading to the development of abrasions or injury. These insults can provide a path for new tumor growth, re-growth of tumors or irritation of otherwise smaller tumors.
Stress has been another factor implicated in FP recrudescence. Hematological parameters, such as white blood cell counts (lymphocytes and heterophils) and stress hormone levels, have been suggested as indicators of immune system stress. These may be altered secondary to behavioral factors that can be impacted by management.1,2,6 Other blood parameters such as calcium, creatine phosphokinase (CPK), and aspartate aminotransferase (AST) may more likely be impacted by an abnormal environment resulting in constant swimming behavior, and can be viewed as indicators of poor behavioral adaptation. By offering visual barriers and hiding places in the pools, changing the viewing aspects from people outside the pool and redesigning pools with limited to no projections in the pool surface, young green turtles may decrease stress related behavior. Alterations of these factors, combined with proper nutrition and good husbandry practices, may decrease the potential and severity of FP recrudescence, shorten FP positive turtles' rehabilitation stay, and lead to more successful releases.
1. Aguirre A.A., and G.H. Balazs. 2000. Blood chemistry values of green turtles, Chelonia mydas, with and without fibropapillomatosis. Comp Haem Int 10: 132-137.
2. Aguirre A.A., G.H. Balazs, T.R. Spraker, and T.S. Gross. 1995. Adrenal and hematological responses to stress in juvenile green turtles (Chelonia mydas) with and without fibropapillomas. Physiol Zool 68(5): 831-854.
3. Herbst L.H. 1994. Fibropapillomatosis of marine turtles. Ann Rev Fish Dis 4: 389-425.
4. Herbst L.H., E.C. Greiner, L.M. Ehrhart, D.A. Bagley, and P.A. Klein. 1998. Serological association between spirorchidiasis, herpesvirus infection, and fibropapillomatosis in green turtles from Florida. J Wildl Dis 34(3): 496-507.
5. Quackenbush S.L., T.M. Work, G.H. Balazs, R.N. Casey, J. Rovnak, A. Chaves, L. DuToit, J. Baines, C.R. Parrish, P.R. Bowser, and J. W. Casey. 1998. Three closely related herpesviruses are associated with fibropapillomatosis in marine turtles. Virology 246: 392-399.
6. Work T.M., R.A. Rameyer, G.H. Balazs, C. Cray, and S.P. Chang. 2001. Immune status of free-ranging green turtles with fibropapillomatosis from Hawaii. J Wildl Dis 37(3): 574-581.