EXPERIMENTAL TRANSMISSION OF GREEN TURTLE FIBROPAPILLOMATOSIS USING CELL-FREE TUMOR EXTRACTS

Green turtle fibropapillomatosis (GTFP), characterized by multiple ben ign fibroepithelial tumors on the skin and eyes, has become a growing threat to green turtle Chelonia mydas populations worldwide. The cause of GTFP is unknown, but a viral etiology is suspected. This study inv estigated whether GTFP could be experimentally transmitted to young ca ptive-reared green turtles using cell-free fibropapilloma extracts pre pared from free-ranging turtles with spontaneous disease. Turtles rais ed from eggs collected from 4 separate clutches in the wild were assig ned to 4 experimental groups and 1 control group. For each experiment a crude homogenate (33% w/v) was prepared from fibropapillomas removed from a free-ranging turtle with spontaneous disease. The crude tumor homogenates were freeze-thawed and centrifuged to yield cell-free extr acts that were used (both filtered and unaltered) for inoculation. Rec ipients were inoculated by intradermal injection or by scarification; control turtles were not treated but were housed with treated turtles. Fibropapillomas developed in all 12 turtles receiving 3 of the 4 tumo r extracts, and were first detected between 15 and 43 wk post inoculat ion. Both filtered and unfiltered tumor extracts successfully induced tumor development. During the 10 and 12 mo monitoring periods, fibropa pillomas did not develop in control turtles or in any turtles inoculat ed with the fourth tumor extract. Although 2 sets of experiments were performed 8 wk apart, most of the tumors in both sets became evident s imultaneously after water temperatures rose. Experimental tumors were histologically indistinguishable from spontaneous fibropapillomas foun d in free-living turtles but lacked evidence of endoparasites. Scatter ed foci of epidermal degeneration were found in most sections of exper imentally induced fibropapillomas and within some sections taken from donor turtles. Electron microscopy revealed virus-like particles confo rming in size, morphology, and intranuclear location with herpesvirus. Negative-staining electron microscopy of transmission-positive tumor extracts failed to demonstrate intact virus particles. This study demo nstrates that the etiology of GTFP is an infectious filterable subcell ular agent. The herpesvirus identified in this study is 1 possible can didate for the etiology of GTFP.