By Melanie Fridl Ross
GAINESVILLE, Fla.---A unique virus genetically related to human herpes viruses could be linked to a serious tumor epidemic threatening the survival of endangered sea turtles worldwide, according to a team of researchers at the University of Florida College of Veterinary Medicine and the Marathon-based Turtle Hospital who first identified it.
Scientists are racing to isolate the new virus so further studies can be conducted to confirm whether it causes the tumors.
The tumors, known as fibropapillomas, erupt on a turtle's soft body tissue and its shell, frequently appearing on or around the eyes, the flippers and even in the mouth. Once the lesions impair the turtle's vision and swimming ability, it has difficulty feeding and ultimately may die.Often the tumors develop within internal organs, such as the lungs and kidneys, and impede normal function.
The research team has detected the virus in more than 95 percent of the tumors plaguing green and loggerhead sea turtles found in the waters surrounding Florida, as well as in tumors on green turtles in Hawaii.
"Transmission studies carried out over the past six years at the Turtle Hospital have demonstrated clearly that this deadly disease is caused by an infectious agent," said Paul Klein, a professor of pathology, immunology and laboratory medicine at UF's College of Medicine and an affiliate professor of pathobiology and small animal clinical sciences at UF's College of Veterinary Medicine. "The fact that this virus is associated with or found in more than 95 percent of tumors does not mean it's the cause of the tumor. But it is a strong candidate for the cause of the disease because infection with it is closely associated with tumor development.
"This is the first virus that we consistently found associated with the tumors and not with normal turtle tissues."
UF researchers presented initial findings on the nature of this novel virus two years ago at the Sea Turtle Symposium in Hilton Head, S.C. Further developments -- including confirmation of the occurrence of a virtually identical virus in the tumors of loggerhead turtles -- will be presented at the International Symposium on Sea Turtle Biology in Matzalan, Mexico this March.
The virus is genetically similar but not identical to human herpes simplex virus 1 and 2 and varicella zoster virus, which causes chickenpox, Klein said, but researchers do not believe the virus can transmit the disease to people.
"Isolating a virus is a major first step in incriminating an infectious agent as a cause of a disease," said Dr. Elliott Jacobson, a professor of wildlife and zoological medicine at UF's College of Veterinary Medicine. "All of us may harbor all kinds of viruses in our body at any one time, and most of those viruses are harmless. So animals may harbor viruses in tumors that are irrelevant -- this has been shown in other diseases. Is this virus the cause of the disease or just growing in the tumor ?"
Researchers first noted a rise in the number of turtles with the lesions in the mid-1980s, and the incidence of the disease has rapidly increased since then, said Ritchie Moretti, who runs the Turtle Hospital in the Florida Keys.
"UF researchers saw the first turtle with internal tumors," Moretti said. "Now 20 percent of the affected turtles have internal tumors. They start out as singular lesions but then may involve most of the soft body areas of an animal. This disease may eventually kill the animal. A turtle can be completely overwhelmed with it in one year, to the point where it can't swim or see any more."
In some cases, veterinarians can intervene and operate to remove the life-threatening lesions, saving the animal's life. But it's a race against time for a cause and a cure. So far, the disease is claiming turtles' lives faster than scientists can save them.
"It takes sea turtles a long time to reach sexual maturity," Klein said. "So what this disease does is it affects juveniles and young adults and removes them from the population so they can't go on to become breeders."
More than 50 percent of the green turtles living in the Indian River Lagoon and Florida Bay are affected, Klein estimated. Nearly 15 percent of the loggerhead turtles in Florida Bay have the disease. In some waters in Hawaii, more than 90 percent of green turtles are stricken with the tumors.
"We're talking about a very serious epidemic," he said. "These tumors have been observed in thousands of turtles."
In 1995, UF researchers and Dr. Richard Garber, of the Seattle-based PathoGenesis Corp., developed a molecular diagnostic test to determine whether the herpesvirus is present in individual tumors and normal tissues.
Meanwhile, research groups at UF, the Retrovirology Research Laboratory at the University of Hawaii and the national Wildlife Disease Laboratory in Madison, Wis., are all working to isolate the virus. UF's research team includes Klein, Jacobson, Moretti and former UF graduate student Dr. Larry Herbst, now of the Albert Einstein College of Medicine.
The research has been supported by the U.S. Fish and Wildlife Service, the National Marine Fisheries Service Honolulu Laboratory, Save-A-Turtle of Islamorada and the Hidden Harbor Marine Environmental Project, Inc., in Marathon.
"This has turned out to be an extremely complicated disease to unravel," Jacobson said. "Multiple laboratories around the continental United States and Hawaii are trying to isolate the infectious agent, and growing this virus out is not easy. A certain amount of luck goes along with being able to do that. You need the right conditions, the right cells, the right samples.
"With that, tests can be developed to look at its prevalence all over the world," he said. "We can then do epidemiological studies to see why it is present in certain areas of the world and what is going on in the aquatic environment where these animals are found to contribute to this problem. Those are really important questions."
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