Fibropapillomatosis of marine turtles

Cutaneous fibropapillomatosis in green sea turtles, Chelonia mydas (GTFP), was first reported over 50 years ago. In the last decade, GTFP has emerged as a significant worldwide epizootic with prevalences as high as 92% in some green turtle populations. Lesions similar to GTFP have been observed in other marine turtle species including olive ridleys, Lepidochelys olivacea, flatbacks, Natator depressus, and loggerheads, Caretta caretta, but disease in these species occurs at lower frequencies and is less well documented. The etiology of GTFP is unknown, and a variety of hypotheses concerning the possible etiology and pathogenesis of GTFP have been proposed and are discussed in this paper. Possible etiologies include viruses, metazoan parasites, ultraviolet radiation, and chemical carcinogens. Recent evidence from controlled transmission experiments implicates a filterable infectious agent as the primary etiology of GTFP. A herpesvirus has been identified in some lesions but has not been isolated and cultured; consequently, Koch's postulates have not yet been fulfilled for this agent. The epizootiology and pathogenesis of GTFP are poorly understood. Epizootiologic evidence, while limited to a few field studies, suggests that environmental conditions in certain near-shore marine habitats favor a high prevalence of disease expression. The possibility that immune system modulators play a role in the persistence and severity of this disease is discussed. Detailed investigations of the epizootiology of GTFP must await identification of the etiologic agent and development of specific diagnostic tests. In addition, until immune function tests can be developed and validated for free-ranging turtles, hypotheses about the role of immune system dysfunction in GTFP epizootics cannot be tested.