HADLEY, Mass. – A new test has revealed that some wild Atlantic salmon in two New England rivers have been exposed to a salmon anemia virus that has caused heavy damage at fish farms, the U.S. Fish and Wildlife Service said Thursday.

Tests done on 1,200 frozen blood samples dating back to 1995 showed that 14 salmon – 10 from the Merrimack River and four from Maine’s Penobscot River – had low levels of antibodies to the virus, fisheries director Dan Kusmeskus said Thursday.

The findings indicate they were exposed to the disease at some point in their life and either did not become sick or survived the disease, he said.

So far, fish returning to the Connecticut River have shown no signs of exposure, Kusmeskus said.

No infected fish were found in federal hatcheries, said Marvin Moriarty, northeast regional director for the agency. “But we remain concerned that the virus can be destructive under the right conditions,” he said.

The virus “poses a threat to Atlantic salmon restoration in New England and the recovery of endangered Atlantic salmon in Maine,” Moriarty said.

At this point it is unknown where the fish might have come in contact with the virus, he said. Still, he said, federal officials were tightening procedures at the hatcheries as a preventative measure.

Atlantic salmon spend the first two years of life in fresh water, then head to the ocean, where they grow into adulthood off Greenland, returning to their native streams only to spawn.

The U.S. Fish and Wildlife Service breeds fish at its hatcheries in Maine, New Hampshire and Massachusetts to rebuild the depleted salmon runs on the Connecticut, Merrimack and Penobscot rivers.

The disease, which is infectious and can be fatal within two weeks, causes fish to become listless and develop pop eyes, swollen livers and internal bleeding.

It was first reported in Norwegian salmon farms in 1984. Since then more than a million farmed Atlantic salmon in Canada, which had a large outbreak in 1996, and in Maine, which had its first outbreak in Cobscook Bay in 2001, have been destroyed to limit the spread of the disease.

“It could be devastating,” Kusmeskus said.

The virus does not affect humans and people cannot contract the disease from eating or handling infected fish, said John Coll, of the U.S. Fish and Wildlife Service’s fish research laboratory in Lamar, Pa.