Evidence is growing that fibropapilloma tumors on green sea turtles are caused by a virus spread by ozobranchus leeches. Advertiser library photo • June 17, 2002

"It's a major step forward," said Llew Ehrhart, professor emeritus at the University of Central Florida, who has studied turtles in Florida for more than two decades. He predicted the discovery would offer important direction for researchers working on the problem.

The disease can be fatal to sea turtles. Others suffer from disorientation, blindness and other handicaps to normal swimming and feeding, increasing the likelihood of predation by tiger sharks, entanglement in fishing lines and impaired migration and breeding.

The study, written by researchers from Cornell University, the National Marine Fisheries Service and U.S. Geological Survey, showed that of the various parasites associated with green sea turtles, only the ozobranchus leeches carry the same virus found in the tumors.

The leech joins the saddleback wrasse, a common reef cleaner fish in Hawai'i, as the only documented likely carriers of the agent causing green turtle fibropapilloma. The disease is specific to the turtle and cannot be spread to humans.

Honolulu turtle scientist George Balazs, one of the authors, said the virus was discovered in the mouth parts and tissues of the leech itself, indicating that the transmission of blood from one turtle to another via the leech doesn't have anything to do with spread of the disease.

Balazs said the green sea turtle is a very social animal and it is likely that the leeches travel from animal to animal when they rub up against each other.

In Florida, Ehrhart has documented the presence of leeches and their eggs on turtles in Indian River Lagoon for years, so the results make a lot of sense to him.

Ehrhart said that his field research also suggests that environmental conditions are a factor as well, with toxins, contaminants and pollutants likely playing a role in promoting the disease.

The good news in Hawai'i, Balazs said, is that the number of fibropapilloma cases appears to have leveled off in recent years. Some turtle monitoring stations indicate that the incidence is actually on the decline, he said, and some turtles with moderate cases have gone into remission and appear to be healthy.

"Five years ago we didn't even think it was possible," said Balazs, who is leader of the National Marine Fisheries Service Marine Turtle Research Program.

In recent years, scientists have removed hundreds of the most severe cases from the wild, a possible explanation for the fibropapilloma decline.

"Or maybe it's just a natural decline in the disease," he said.