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

Green turtle fibropapillomatosis (GTFP), characterized by multiple benign 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 investigated whether GTFP could be experimentally transmitted to young captive-reared green turtles using cell-free fibropapilloma extracts prepared from free-ranging turtles with spontaneous disease. Turtles raised from eggs collected from 4 separate clutches in the wild were assigned 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 extracts that were used (both filtered and unaltered) for inoculation. Recipients 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 tumor extracts, and were first detected between 15 and 43 wk post inoculation. Both filtered and unfiltered tumor extracts successfully induced tumor development. During the 10 and 12 mo monitoring periods, fibropapillomas did not develop in control turtles or in any turtles inoculated with the fourth tumor extract. Although 2 sets of experiments were performed 8 wk apart, most of the tumors in both sets became evident simultaneously after water temperatures rose. Experimental tumors were histologically indistinguishable from spontaneous fibropapillomas found in free-living turtles but lacked evidence of endoparasites. Scattered foci of epidermal degeneration were found in most sections of experimentally induced fibropapillomas and within some sections taken from donor turtles. Electron microscopy revealed virus-like particles conforming 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 demonstrates that the etiology of GTFP is an infectious filterable subcellular agent. The herpesvirus identified in this study is 1 possible candidate for the etiology of GTFP.