Deadly virus hits turtles, tadpoles in Montgomery County
By Katherine Shaver,
Maryland biologists studying box turtles rescued from the bulldozers on the Intercounty Connector construction site have made a grisly find: An alarming number of the tiny turtles later died, and biologists say their demise appears to be unrelated to the highway.
Worse yet, the cause of their death — an animal disease called ranavirus taking root across the United States — also is believed to have killed nearly every tadpole and young salamander in the study area in Montgomery County’s North Branch Stream Valley Park since spring 2010.
The discoveries have alarmed state wildlife officials and biologists, who worry about how far ranavirus has spread, how widely it has affected the ecosystem, and how it apparently jumped between turtles — which are reptiles — and amphibians. If the virus spreads or goes unchecked for long, wildlife experts say, it could devastate some local populations of box turtles, frogs and salamanders. That loss, biologists say, would ripple along the food chain to other animals.
In all, 31 adult turtles were found dead near the ICC construction site between 2008 and 2011. Three had been hit by cars or construction equipment. The rest, apparently dead from illness, amounted to about one-quarter of the turtles monitored by Towson University researchers via radio transponders glued atop the tiny shells. Twenty-six of the deaths resulted from suspected or confirmed cases of ranavirus, which left some turtles gasping for breath as they gradually suffocated in their own mucus, researchers said.
“Finding even one dead turtle is unusual,” said Richard Seigel, the Towson biology professor who led the ICC study. “Finding over 27 dead turtles in a two-to-three-year period was bizarre.”
Box turtles can live 50 years or more in the wild. The ability of their hard shells to withstand predators usually affords them a 98 percent survival rate from one year to the next before they die of old age, usually alone and undetected beneath brush, Seigel said.
“This is a major concern to see these emerging pathogens,” he said.
Experts on animal diseases say ranavirus, whose origin is unknown, has never been detected in humans, livestock or common household pets because it cannot survive in mammals’ relatively warm bodies.
Its long-term effects on local turtles, frogs and salamanders are not yet known and will depend on how long the virus lingers, how far it spreads and how quickly surviving animals build up immunity, biologists said. But several wildlife experts said the disease’s short-term effects are probably affecting the food chain in the ICC study area between Muncaster Mill Road and Emory Lane, just west of Georgia Avenue in northern Silver Spring.
The birds, snakes and raccoons that dine on salamanders and tadpoles have less food at their disposal, experts say.
Meanwhile, the loss of hundreds, perhaps thousands, of tadpoles and salamander larvae wiped out in two consecutive breeding seasons has probably left far more of the insects that young salamanders and frogs eat.
“What is the ecological significance of a virus that can kill every one of an animal’s offspring? The implications of that baffle me,” said David Green, a veterinary pathologist at the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wis.
Wildlife experts say they’re also concerned that the sudden appearance of ranavirus, a disease that some believe has been lurking in the United States for a century, might signal that local ponds and wetlands are becoming more susceptible to disease under the stresses of climate change, pollution and development.
“Amphibians are very good indicators of the health of our ecosystem,” said Scott Smith, a wildlife ecologist for Maryland’s Department of Natural Resources. “When we see things happen to them, it means our environment is unhealthy.”
Green, the veterinary pathologist, said ranavirus causes measles-like or severe herpes-like symptoms. Often, turtles discharge mucus from their eyes and noses. He said the virus damages their skin, palate, esophagus, stomach, liver, spleen and blood vessels. ICC researchers said they found some turtles dead within four days of their first symptoms.
The ICC tadpoles and young salamanders became sluggish and were seen swimming off-kilter before bleeding into the skin of their bellies, thighs and feet.
“It’s a really, really, really horrible disease,” Seigel said.
Ranavirus, first identified in the United States in 1968, has been suspected or confirmed in turtle and amphibian deaths in 29 states 71 times since 1997, according to the USGS, which tracks animal diseases at its National Wildlife Health Center.
Maryland’s first confirmed case came in 2005, when it and the Chytrid fungus killed more than 2,000 young wood frogs and spotted salamanders near Montgomery’s portion of the C&O Canal, Smith said. Since 2000, ranavirus has been confirmed in Anne Arundel, Prince George’s and Baltimore counties.
Virginia’s only confirmed outbreak hit in 2003, when ranavirus killed 20 Southern leopard frogs in the Virginia Beach area, according to the USGS. No cases have been reported in the District.
Ken Ferebee, a National Park Service wildlife specialist in the city’s Rock Creek Park, said he’s seen no signs of the disease in the box turtles and pond life that he monitors about 12 miles south of the Montgomery outbreak area. He said he hopes box turtles’ slow pace and propensity to stick close to home will keep the disease contained near the ICC.
“I don’t think it’s something we can stop,” Ferebee said. “If we find it in the park, it will probably be way too late.”
The Towson University findings, which are just beginning to circulate among biologists in the Northeast, stemmed from a $300,000 state-funded study of how to best save the turtles that, unlike deer and foxes, needed help to escape 18 miles of woods and wetlands ahead of the bulldozers. A team of Towson students attached radio transmitters to 123 of the more than 900 turtles rescued, allowing them to track the animals’ every move.
The idea was to study whether the turtles fared better by being relocated about six miles away or to an adjacent area separated from the construction site by a fence. The study was considered potentially important to highway agencies and developers across the country, who are under pressure to reduce the environmental effects of road and building construction.
Rob Shreeve, the Maryland State Highway Administration’s ICC environmental manager, said the study was helpful in concluding that the turtles’ survival rates — even with ranavirus — were about the same even when they were moved to different locations with similar living conditions.
Seigel, the Towson researcher, said he has no data to show that turtles that were moved from the ICC’s path started the outbreak or were more susceptible to illness. He said his team checked the turtles’ mouths, eyes, noses and weight to make sure they were healthy before moving them.
The ranavirus death rate in turtles that were moved from the ICC site was roughly the same as the mortality rate in a control group of turtles that already lived in the area and never relocated, Seigel said. The apparently fast-acting virus didn’t begin affecting any of the turtles until about 18 months after the ICC animals were moved, making it less likely that the relocation was at the source, he said.
Smith of the Natural Resources Department said state wildlife officials are so concerned that they have applied for research funding from the Association of Reptile and Amphibian Veterinarians. State budgets are too strapped to fund the necessary research, he said.
Scott Farnsworth, Seigel’s graduate research assistant on the ICC study, said he’s less worried about the local amphibian population’s ability to recover because frogs and salamanders begin breeding when they’re a few years old and each lay hundreds of eggs. If the virus dies off soon, he said, the overall population could bounce back relatively quickly.
But the population of tiny box turtles, most so small that they fit in the palm of a hand, isn’t as resilient, he said. Box turtles don’t breed until they reach 10 to 15 years old and females typically lay only eight to 10 eggs per year, he said. That means it wouldn’t take as long for a virus killing off reproductive adults to send the species into a steep decline.
“If it’s chronic, it could have devastating impacts on the turtle population,” Farnsworth said. “It could take decades for them to recover from it, if they do recover.”
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