Dolphin strandings for July and August are more than nine times the recent historical average for the Mid-Atlantic region, according to NOAA Fisheries.
From the beginning of July through Monday, 356 bottlenose dolphins have come ashore from New York to North Carolina. Of the total, 72 strandings occurred in New Jersey.
Officials also have received numerous reports of dead animals floating offshore, but given the effects of wind and current, they are unable to respond.
When it will end - and after how many deaths - is unknown.
So far, the disease is following a similar track of a morbillivirus outbreak that lasted from August 1987 to May 1988, during which about 740 animals died.
That outbreak required a years-long recovery period for the population, said Lance Garrison, with the NOAA Fisheries Southeast Fisheries Science Center in Miami.
Now, with so many strandings again, "there is concern it could have a significant population impact," he said.
Typically, an outbreak lasts "as long as there are susceptible animals that can be infected," Rowles said. Using the 1987-88 outbreak as a road map, "we're looking at mortalities being higher . . . and likely continuing until the spring of 2014."
They also expect the outbreak to spread southward as the dolphins migrate.
Meanwhile, "there isn't anything we can do to stop the virus," Rowles said. In terrestrial populations of wildlife or domestic animals, vaccines are often available.
But, she said, "we don't have a vaccine developed that could be easily deployed in a wild population of bottlenose dolphins."
What they expect is that as the virus moves through the population - spread by respiration and contact - some dolphins will die, and others will gain immunity, said Stephanie Venn-Watson, of the National Marine Mammal Foundation in San Diego.
Gradually, the entire population will become resistant, and officials will see only sporadic cases among young dolphins.
Officials also are unsure how or where the outbreak originated.
So far, it seems to be a classic case of a virus being introduced to a "naive" population - one that hasn't been exposed recently, or ever, said Venn-Watson.
So scientists will be looking at animals that were stranded earlier in the spring for clues. They think it's possible that populations of cetaceans - dolphins and their relatives - living farther offshore exposed the inshore migratory populations that now seem to be affected.
Scientists also will continue to look at potential secondary factors, including water pollution.
Bottlenose dolphins along the Atlantic coast - in particular, one population off the coast of a Georgia Superfund site - "have high level of PCBs and other chemicals that can have an impact on immune function," Rowles said.
NOAA Fisheries has formally declared the die-off an "unusual mortality event," which prompts federal oversight of an investigation and loosens some federal money to fund it.
With the virus, many dolphins have lesions on their skin or in their mouths, joints, or lungs.
The virus is not transmissible to humans or shellfish, officials said.
Nevertheless, officials warn people not to touch or let their pets come into contact with stranded animals.
They ask that anyone finding a stranded dolphin report it to a marine mammal stranding hotline at 1-866-755-6622.
Contact Sandy Bauers at 215-854-5147, firstname.lastname@example.org, or follow on Twitter @sbauers. Read her blog, "GreenSpace," at www.inquirer.com/ greenspace.