Serial cultivation of cell lines derived from lung, testis, periorbital skin and tumor tissues of a green turtle (Chelonia mydas) with fibropapillomas resulted in the in vitro formation of tumor-like cell aggregates, ranging in size from 0.5-2.0 mm in diameter. Successful induction of tumor-like aggregates was achieved in a cell line derived from lung tissue of healthy green turtles, following inoculation with cell-free media from these tumor-bearing cell lines, suggesting the presence of a transmissible agent. Thin-section electron microscopy of the cell aggregates revealed massive collagen deposits and intranuclear naked viral particles, measuring 50 ± 5 nm in diameter (Figures 8 and 9). These findings, together with the morphological similarity between these tumor-like cell aggregates and the naturally occurring tumor, suggest a possible association between this novel virus and the disease. Further characterization of this small naked virus will clarify its role in etiology of GTFP, a life-threatening disease of this endangered marine species.

Figure 8. Thin-section electron micrograph of green turtle lung cell line. (A) Vacuolar formation within cytoplasm and virus particles packaged within hypertrophic nuclei of affected cells; and (B) electron-dense cell with hypertrophic nucleus.

Figure 9. Thin-section electron micrograph of green turtle lung cell line. Naked virus particles appear either (A) scattered or (B) crystallized within the nucleus of affected cells.