Comparative pathology and pathogenesis of spontaneous and experimentally induced fibropapillomas of green turtles (Chelonia mydas)

Tumor biopsy samples from 25 Floridian and 15 Hawaiian green turtles (Chelo nia mydas) with spontaneous green turtle fibropapillomatosis (GTFP) and fro m 27 captive-reared,green turtles with experimentally induced GTFP were exa mined microscopically to differentiate the histologic features that result from GTFP pathogenesis and those that result from incidental factors that m ay vary according to geographic region. Common histologic features for spon taneous and experimentally induced tumors included fibroblast proliferation in the superficial dermis, epidermal acanthosis and hyperkeratosis, epider mal basal cell degeneration with dermal-epidermal cleft formation, spinous layer degeneration with intraepidermal vesicle and pustule formation, and u lceration. Visceral tumors, found in eight of 10 (80%) free-ranging turtles with cutaneous disease that were examined after death, had extensive inter stitial fibrous proliferation. The presence of spirorchid trematode eggs an d associated foreign body granulomas, common secondary findings within spon taneous tumors, varied by geographic location, and these findings were not observed in experimentally induced tumors. Eosinophilic intranuclear inclus ions and intranuclear herpesvirus-associated antigen immunoreactivity were found in 18 of 38 (47%) experimentally induced cutaneous tumors and nine of 119 (7.5%) spontaneous tumors from Floridian but not Hawaiian turtles. The possible involvement of GTFP-associated herpesvirus in the pathogenesis of epidermal degenerative changes and GTFP pathogenesis is discussed.