 The pictures are shocking. The young adult green sea turtle (Chelonia mydas) is covered with pulpy frills. Its eyes are masked with folds of tissue, like a badly beaten boxer. For divers around the world, images like this come to life all too frequently. And the horror of a disease called fibropapilloma is very real.
Already threatened by overharvesting, habitat destruction, entanglements and drowning in fishing nets, green sea turtles have faced a fight for their lives against this mysterious disease. By infecting the next generation of breeding turtles, fibropapilloma may push the species to the brink of local extinction. But there is renewed hope on the horizon, as incidents of the disease appear to be tapering off.
“In the [French Frigate Shoals, Hawaii] population as a whole, we’re seeing a level of growth, and at some of our survey sites, we’re seeing fewer turtles with disease. And in those, it’s not as severe,” says George Balazs of the National Marine Fisheries Service in Honolulu. “Things appear to be improving, but it’s hard to pin down with scientific data.”
He would know. Balazs has studied the turtles for more than 30 years and was instrumental in having the animals listed on the U.S. endangered species list. He’s also one of a handful of scientists who are searching for the cause of the disease. Those scientists are weeding through a maze of evidence implicating different viral and environmental causes for the tumors. Yet, much of their research is in its early stages. They’ve got a long way to go.
Identifying a Disease
Biologists and veterinarians call fibropapilloma a pandemic — a global epidemic. It’s been found throughout the Caribbean, along the Atlantic coast of Florida, the Pacific Rim, Hawaii and Australia. It’s most prevalent in shallow coastal areas with slow water turnover. What’s most disconcerting is that the disease was a rarity even into the 1950s, ’60s, and early ’70s, before tearing through populations in the 1980s and ’90s.
Fibropapilloma tumors look like large warts. Each has a cauliflowerlike texture and grows on the soft tissue between the turtle’s shells, including the neck, eyes, mouth, and the areas under the fins. They can be black, pink or white. Tumors can weigh up to 3 pounds, but typically range in size from less than a centimeter to about the size of a football.
In the 1980s, turtle strandings in Hawaii were relatively uncommon, with less than two dozen cases annually. By the late 1990s, between 200 and 300 strandings were recorded each year. Between half and about 70 percent of stranded turtles in Hawaii have tumors. In Florida’s Indian River Lagoon, infection rates reached nearly 73 percent in 1998, and earlier this year, 48 percent of turtles debilitated in a cold-weather snap were positive for the disease. In other parts of the world, infection rates are as high as 92 percent. Infected turtles are emaciated and anemic, their collapsed plastrons evidence that they’re starving to death.
The tumors themselves are benign — on their own, they won’t kill the turtles. But they can impair the turtle’s vision and swimming ability. At its worst, the turtle can’t hide from predators, and its immune system can’t fight the infections it’s exposed to. If the turtles are still alive after they’ve stranded, they are collected and sent to state turtle veterinarians, where they’re X-rayed and examined internally with an endoscope for evidence of internal tumors. The presence of tumors in the animal’s lungs, liver, kidneys, and gastrointestinal tract indicate an advanced stage of the disease and are always fatal. Instead of allowing the turtle to succumb to pressure necrosis of internal organs, kidney failure and bowel obstructions, the animal is euthanized.
If the disease hasn’t advanced to that stage, the external tumors can be removed with lasers, and the turtle has a good chance of survival and return to the wild. But surgical removal is a ham-fisted solution to a disease that scientists know very little about. There’s still debate over how the disease is caused and how it’s spread — and if rerelease is such a good idea after all.
 It’s not as if green sea turtles needed another problem. The species got its name from the color of the fat inside its shell, which is a pretty good clue to their biggest problem. Fished nearly out of existence to feed tourists’ taste for exotic meat, it was listed in 1978 as a threatened species in Hawaii and an endangered species in Florida. They’re still threatened by commercial and subsistence hunting in other parts of the world.
Total global turtle population numbers are anyone’s guess. The number of nesting turtles in the Hawaiian population appears to be going up, as it is in Tortuguero, Costa Rica, Archie Carr National Wildlife Refuge in Florida, and Sabah, Malaysia. Unfortunately, most infected turtles are young ones — juveniles that represent the next breeding generation. Within that group, more females are infected than males.
Potential Causes
You’d have to look long and hard to find a green sea turtle in New York City, but that’s exactly where you’ll find most of the research on what makes the disease tick. Dr. Lawrence Herbst is a veterinarian at the Institute for Animal Studies at Albert Einstein College of Medicine, and while a student at the University of Florida he was first to show that fibropapilloma was contagious and that it is likely caused by a virus. Now, he studies the disease in his free time.
While at Florida, Herbst infected disease-free turtles by injecting them with an extract made from tumor cells — a standard preliminary test for an “infectious agent,” such as a virus or bacteria. He’s also observed that control turtles that hadn’t been injected with the tumor extract have also developed tumors after being kept in the same aquarium for several months as infected turtles. He thinks the disease is caused by a herpes virus — similar, but not identical, to the human herpes simplex 1, herpes simplex 2, and herpes zoster virus, which causes chickenpox.
But Herbst hasn’t been able to culture the fibropapilloma herpes virus — a key step in laying scientific blame. That makes in-depth study of even the most basic traits of the virus difficult. However, other researchers have been able to study another turtle herpes virus, one that is stable in sea water and can remain infective outside the turtle. That shows turtles don’t need to have physical contact to catch that particular virus. Herbst is eager to test the virility of the green turtle fibropapilloma herpes virus, once he can develop a pure culture.
“It may never be provable,” Herbst says. “You need a pure form of the infective agent, and it’s hard to get a pure virus — there can be other agents that exist in the culture. We have to show infection with an isolated virus particle.”
Even so, Herbst’s research process may allow scientists to test possible infection mechanisms. “Part of the problem is we don’t have the right tools to ask the questions,” Herbst says. “A lot of what I’m working on is to develop these tools.”
We just don’t know the basic ecology of the disease, he says. For example, the fibropapilloma herpes virus has been found in tissue of wrasses, cleaner fish that pick algae and parasites off sea turtles at cleaning stations. They may be a “vector” that transmits the virus between animals, though the fish appear to prefer cleaning nontumored areas of infected turtles than the tumors themselves.
Scientists are also researching for environmental causes for the tumor outbreaks, which are often localized. Balazs said that of the 2,377 recorded strandings, 75 percent occurred on Oahu, home to three-quarters of that state’s population but only 15 percent of its coastline. Another 13 percent occurred in Maui. No turtle with fibropapilloma has been found on the Kona/Kohala coast, along the undeveloped western edge of the island of Hawaii, or in St. Joseph Bay, Florida, two areas of high turtle concentrations.
Balazs thinks the disease is related to human perturbations of the turtle’s feeding areas. According to this theory, turtles are eating a dinoflagellate, a type of single-cell plankton. Several species of the genus of concern, Prorocentrum, secrete the toxin okadaic acid, which has produced tumors in laboratory mice.
Prorocentrum are common throughout the world in low numbers, but during Harmful Algae Blooms (HABs), the algae jump high above normal levels. HABs, which often occur naturally, are intensified if there are high nutrient levels in coastal water. Nutrient loading results from runoff from agriculture, industrial outflow, sewage treatment facilities, urban wastewater, and alterations of estuary circulation — all symptoms of coastal development. Nutrients become food for algae, and the turtle consumes the Prorocentrum — and the okadaic acid — as it grazes.
In Hawaii and Florida, areas of high fibropapilloma infection rates coincide with high levels of Prorocentrum, and areas of low tumor rates coincide with lower toxin levels. High fibropapilloma rates also coincide with regions where preferred turtle food is also a preferred “host” for Prorocentrum.
While sea turtle hatchlings are nomadic for the first three to six years of their life, drifting along with ocean currents, they settle once they become about dinner-plate sized. From then on, they spend much of their lives grazing on algae and seaweed in near-shore waters and sleeping beneath protective underwater ledges. They take more than two decades to reach breeding age. Turtles generally feed in the same area all the time, leaving only to migrate every two to five years to nest. “We have turtles tagged 15 or 20 years ago still living in the same general half-mile stretch or less of coastline,” he says. He thinks the cumulative effect of the toxin could be what causes the tumors.
On the other hand, several high fibropapilloma sites had low Prorocentrum levels. One possible explanation is that environmentally stressed dinoflagellates actually produce more potent toxins. At the very least, toxins could be suppressing the immune systems of the animals, leaving them ripe for additional infections by another tumor-causing agent — including a herpes virus or retrovirus.
That’s all well and good, but some research indicates turtles with the disease don’t have suppressed immune systems. Further surveys indicated some turtles don’t develop tumors, or they do then go into regression. That may mean there may be a genetic link to fibropapilloma susceptibility. There may also be several different variations to the fibropapilloma agent — in Hawaii, tumors are common in the soft tissue of the turtle’s mouth. Oral tumors haven’t been spotted anywhere else in the world.
For those reasons, Herbst is skeptical of the environmental link. It’s a nice idea, he says, but he prefers to spend his time studying the fundamentals of the herpes virus.
If Prorocentrum doesn’t prove to be the cause, Balazs is looking for other potential environmental links. “We are now working with a Ph.D. student from Australia focusing on the blue-green alga, Lyngbya, that’s known to have toxic properties and possible tumor-promoting properties. The student is sampling to compare Hawaii and Moreton Bay off Brisbane where there’s high green turtle tumor prevalence in certain segments of the bay,” he says.
Solving the Puzzle
There is some good news. “The FP disease seems to be leveling out and declining,” Balazs says. “We see about 30 percent prevalence of the disease now at study sites such as Kaneohe Bay, Kailua Bay, and Palaau on Molokai. In addition, the cases we see during our in-water catching sampling work are now often less severe than in past years. However, in our stranding program we are still getting severely debilitated, terribly sick turtles with tumors.”
 Those turtles that are most sick may help researchers the most. Balazs says that when the turtles present with severe fibropapilloma symptoms, their tissues are used to study blood chemistry, virology, bacteriology, genetics, and immunology, as well as age and sex-ratio information. He says matter-of-factly that when the turtles die from the disease, they “send them to heaven, but study them to hell.” Basic science comes slow and hard.
For human medicine, figuring out the structure of the fibropapilloma herpes virus could lead to figuring out how other similar human diseases work. That could mean potential breakthroughs in Kaposi’s sarcoma, human genital herpes, Epstein-Barr Disease, and other virus-induced tumor-forming diseases. “Knowing the basic mechanisms can lead to understanding of how viruses work,” Herbst says, but success in one animal doesn’t necessarily mean success in another.
“I don’t have high hopes of curing people,” he says.
If there is an environmental connection between fibropapilloma and algae blooms, then resources managers like Balazs are faced with ways to reduce nutrient loading in coastal waters for the sake of turtles. That may be just as impossible a task as immunizing thousands of turtles against an opportunistic virus.
In the meantime, there are difficult questions that still need to be answered. With hard work and some good fortune, they may find some answers. Perhaps then, the horrid pictures of the infected turtles will be only a record of the past, not a risk for their future.
For More Information
“Fire in the Turtle House:
The Green Sea Turtle and the Fate of the Ocean”
by Osha Gray Davidson, PublicAffairs Press
Florida Marine Research Institute
Turtle Trax
The Turtle Hospital
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