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Background: Sea turtles are one of the oldest groups of reptiles and are found worldwide. There are seven species of sea turtles in the world, and Hawaii has two of them, the hawksbill and the far more numerous green turtle. Threats to turtles include bycatch from fisheries activity, overharvesting of eggs on nesting beaches, and disease. Of the latter, the most significant disease of sea turtles is called fibropapillomatosis (FP). Since 1995, the Honolulu Field Station and National Marine Fisheries Marine Turtle Research Program have had an ongoing collaboration to elucidate the cause and epizootiology of FP. |
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Fibropapillomatosis causes unsightly external and internal tumors in sea turtles. It affects mainly green and loggerheads and is found in almost all the tropical marine ecosystems where these species reside. FP has also been documented in other species of sea turtles, but much more infrequently. FP was first described in green turtle from Florida in the early 1920s. In Hawaii, the first record of the disease occurs somewhere about the early to mid 1950s. FP affects mainly immature turtles, and in Hawaii, the percentage of individuals affected can range from 20 to 40% depending on the location and method of sampling. In addition to causing tumors on the skin, eyes, and mouth (photo at left), about 20-30% of sea turtles with the disease also have tumors in internal organs such as the lungs, kidneys, and heart. |
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What causes FP? FP was deemed not much more than a curiosity until the 1980s and 90s when serious research began on the disease. Microscopic examination of tumors by the University of Florida, Gainesville, revealed particles suggestive of a herpes virus. Since herpes viruses are known to cause tumors in animals and humans, this agent as a potential cause of FP was certainly plausible. However, many other things can cause tumors in animals. Investigators in Florida then attempted to reproduce the disease in captive green turtles. In order to do this, they took tumors, homogenized them, and passed them through special filters that eliminate all but the smallest particles (viruses). They then injected this material in turtles and were able to reproduce tumors similar to those seen in the wild. This was very compelling evidence that whatever caused the disease, it was either something very small (maybe a virus or protein) but almost certainly not something like a bacterium or parasite that would have been eliminated in the filtration process. |
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Evidence for a virus: During the late 1990s, a collaborative study between National Marine Fisheries Service Honolulu Laboratory, Cornell University and the Honolulu Field Station using molecular tools found that genetic material from herpes virus was found predominantly in tumored tissue of Hawaiian green turtles but not normal tissue (including internal tumors such as the large white mass pictured at left). Subsequent investigations of green and loggerhead turtles with FP from Florida confirmed this finding. Unfortunately, the story does not end here. The mere association of a virus with diseased tissue does not necessarily imply cause and effect. After all, there could be something about tumor tissue that allows this herpes virus to replicate. A logical next step would have been to isolate the virus, inject it into an animal, and see if FP can be reproduced. Unfortunately, isolating live virus in the laboratory has proved fiendishly difficult, so the hypothesis of herpes virus as a cause of FP remains just that, a hypothesis. |
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Effects of FP on turtles: FP is the primary cause of stranding of sea turtles in Hawaii. This alone implicates that it is probably having detrimental effects to turtles. Turtles with severe FP become immunosuppressed and get secondary bacterial infections. To top it all off, many stranded turtles have concomitant infections with worms that live in blood vessels and cause inflammation of internal organs. Hawaii is also unique in that turtles here get tumors in the glottis (opening to the trachea as pictured at left). This prevents closure of the glottis allowing seawater and food to get into the lungs. Not surprisingly, many turtles that strand with glottal tumors also have infections and inflammation in the lungs. A system to score the severity of FP in Hawaiian green turtles devised by National Marine Fisheries Honolulu Laboratory and the Honoloulu Field Station indicate that animals with moderate to severe disease have a lower likelihood of being resighted. All this implies that FP is more than a mere cosmetic disease and warrants further investigation. In addition, the disease affects mainly immature turtles, and loss of this age group poses the most serious implications for sustainment of turtle populations. |
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Where to go from here? In order to have any hope of managing this disease, several critical pieces of information are needed. How is the virus transmitted? Why does FP show up more often in what appear to be "degraded" habitats? Does the herpes virus cause the tumors? What are the effects of the disease on turtle populations? Why does it show up in certain areas and not others? The presence of a highly visible disease in a large animal like the turtle suggests something is awry with the ecosystem. Understanding why this is so may add a piece to the puzzle of sustainable management of marine ecosystems. There is hope, however. Recent data analyses by NMFS suggest that in some areas, the prevalence of FP is decreasing. Reasons for this are unknown. |
