Among five other species tested, the virus has been detected in three humpback whales and two pygmy sperm whales that stranded in Massachusetts, Virginia, North Carolina, and Georgia.
So far, officials know only that the animals were exposed to the virus. "What we're trying to figure out is if it caused clinical disease in these animals" that led to the strandings, said Mendy Garron, regional stranding coordinator with the National Oceanic and Atmospheric Administration's fisheries division.
It's also possible some other disease or pathogen caused the whales to strand, and the virus was simply present as well.
"This is something we're going to monitor very closely," Garron said.
If the virus has caused disease in some whales, concerns ramp up significantly for North American right whales, one of the most endangered species on the planet.
Fewer than 400 right whales exist, and they calve from December through March in the coastal waters off Georgia and northern Florida - where dolphin strandings have spiked as the animals migrate southward.
Fortunately, "a lot of research goes on around that time," Gerron said. She said that researchers would pay attention and that if they see dead whales, "obviously, test them."
It's also unclear how the humpback and pygmy sperm whales could have become infected, said Bob Schoelkopf, director of the Marine Mammal Stranding Center in Brigantine, a nonprofit that responds to marine animal strandings in New Jersey.
The latest die-off has been officially declared an "unusual mortality event," prompting federal oversight of the probe and a loosening of funds to do it.
In August, New Jersey officials stepped in to help Schoelkopf's group, whose funds were depleted by the number of animals they had to deal with.
The state agriculture department offered its Ewing Township lab for necropsies of dead animals; before that, the carcasses had been driven to the University of Pennsylvania's New Bolton Center, a large-animal veterinary facility in Kennett Square. So far, 26 dolphins have been processed at the New Jersey lab.
Before the most recent stranding, in North Cape May, the last stranding had been Nov. 6.
The virus has been identified as morbillivirus, akin to measles in humans and distemper in dogs.
A similar - but, it turns out, lesser - die-off of dolphins occurred along the Atlantic Coast in 1987-88.
Officials expect the virus will run its course in bottlenose dolphins this winter, perhaps infecting resident populations in southern waters, said Teri Rowles, head of the NOAA Fisheries Marine Mammal Health and Stranding Response Program in Silver Spring, Md., during a recent teleconference.
Animals that survive to migrate northward in the spring will likely have developed an immunity. That's what happened in the 1987-88 die-off.
What also happened, however, is that humpback whales started stranding in New Jersey that spring.
Sadly, Schoelkopf said, those whales weren't tested for morbillivirus. But he's worried that they had it then and could now. They could mix with the dolphins as they head to their breeding area on the Silver Bank, 1,100 square miles of shallow water between the Dominican Republic and Puerto Rico.
Schoelkopf has been there, in the water with thousands of them. Ecotourism boats now take people there to snorkel or free-dive among them.
"You could hear them," he said. "It's a beautiful place. The problem is that if any of the humpbacks that were diseased carried it down to the Silver Bank, it may be a long time before anyone even recognizes what's going on."