SEBASTIAN, Fla. — Half the endangered green sea turtles in the Indian River Lagoon suffer from life-threatening tumors, caused by a herpes virus that doesn’t infect us, but that we make worse for turtles.
Our pollution likely worsens the pathogen’s impact on sea turtles, research is finding. The tumors it causes can grow as large as tennis balls, hampering the turtle’s ability to swim or starving them when neck tumors clog their throats.
The debilitating disease, called fibropapillomatosis, was first identified in 1938.
But, after decades of research, the exact cause remains a mystery.
So University of Central Florida biologists are delving into DNA to figure out why some turtles appear immune to the disease and why different strains of the virus are more harmful than others.
“Some of those lineages might be the ones that are actually causing the tumor disease to occur in the turtle, whereas others might be more benign,” said UCF molecular ecologist Anna Savage, standing at the Sebastian Inlet boat ramp, readying to go out and net turtles.
But pollution levels where the turtles live also might be worsening the disease.
“That is a very good hypothesis,” Savage said.
Studies have pointed to organochlorine compounds that persist in the environment and suppress turtles’ immune systems. Those compounds also have been linked with immune suppression and carcinogenic effects in humans.
Flame retardants and pesticide byproducts are showing up at potentially toxic levels in sharks, rays and other marine life in the lagoon and in the ocean just off Brevard County, according to research in recent years by the Fish and Wildlife Research Institute. Other studies also have detected flame retardants and pesticide byproducts in sea turtles, dolphins, alligators and other wildlife in east Central Florida.
But with the viral tumor disease in sea turtles, Savage says DNA differences might explain why researchers see as many infected turtles with tumors as without.
She recently teamed with UCF assistant professor and biologist Kate Mansfield Savage to collect turtle and viral DNA. Mansfield recently earned a $17,631 grant from the nonprofit Sea Turtle Conservancy to study the DNA differences driving the tumor disease among green and loggerhead sea turtles.
Little is known about the death rates from the tumor disease. Some older turtles show signs of regressed tumors.
The proportion of lagoon green turtles with tumors has remained fairly steady, averaging 50 percent, since long-term sampling began in 1983, the UCF researchers said. Rates are much lower in loggerheads.
“It’s really difficult to quantify, because there aren’t that many in-water studies,” Mansfield said of the incidence of the disease in the lagoon. “It’s stayed fairly consistent in terms of the number of turtles that have it.”
State data shows 22.2 percent of dead or debilitated green turtles found in Florida between 1980 and 2005 had fibropapilloma tumors, according to data gathered by state wildlife officials. But the green turtles researchers find in the lagoon have for years consistently suffered from the tumor disease at about twice that rate.
The virus that causes the tumor disease is unique to sea turtles, but falls within the same family as the herpes viruses that infect humans.
The lesions from the disease have been reported in all sea turtle species except in leatherbacks.
The tumors can interfere with vision, feeding and ability to escape predators.
Savage’s research focuses on the role genes play in disease resistance.Most of her work has been with frogs, until now.
Mansfield and her students net and release sea turtles in the lagoon near Sebastian Inlet to collect data and monitor their health.
A recent mission was a bust, when too many dolphins lingered nearby for too long. The researchers’s federal permit doesn’t allow them to drop the 500-foot-long net when dolphins or manatees are in the area.
The biologists collect samples of blood and skin, and check for tumors. They then tag the turtles’ flippers and release them.
Mansfield and the UCF turtle team’s work helps state and federal wildlife managers better protect the endangered and threatened species.
But will the DNA research lead to a cure?
In terms of a vaccine, researchers can’t even say for sure yet whether the herpes virus is the definitive cause of the tumors.
“Therefore, I think it’s premature to try to vaccinate against it,” Savage said. “However, that would be an interesting avenue of future research if we continue to find associations between having the disease, being infected with the herpesvirus, and the variation in immune genes of the turtles.”
Information from: Florida Today (Melbourne, Fla.), http://www.floridatoday.com