Deadly virus hits turtles, tadpoles in Montgomery County

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.

Video

A female box turtle exhibits gaping behavior as it attempts to breath. The yellow and black colored plaques seen inside the mouth and throat of this animal are signs of a potential Ranavirus infection and are caused by dying tissue. The gaping behavior being exhibited is the animal struggling to breath and trying to clear its lungs and throat of the necrotized tissue. (No audio) (Feb. 9)

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.

Ecological implications

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.