A deadly virus killing hundreds of dolphins along the East Coast likely won’t last, biologists say.

But the virus can be expected to return periodically.

The “unusual mortality event” has killed at least 330 dolphins in cases confirmed so far from New York to North Carolina — more than half of them in Virginia, according to the National Oceanic and Atmospheric Administration. Biologists have raised alarms that the outbreak will move south through the Lowcountry to Florida, as did a similar outbreak in 1987-88.

During that outbreak of the morbillivirus, surviving dolphins developed or strengthened an immunity to it. The immunity evidently breaks down through succeeding generations, said Stephanie Venn-Watson of the National Marine Mammal Foundation.

NOAA biologists also will be studying the dolphin carcasses to see if something in the environment weakened the dolphins to make them susceptible to the virus, said Lance Garrison of NOAA Fisheries Southeast Fisheries Science Center.

The 1987-88 morbillivirus outbreak eventually killed about 740 animals, including 42 of 79 deaths in South Carolina, according to NOAA. The virus has been found in more than nine of every 10 animals tested so far in this outbreak.

So far, no strandings in South Carolina appear to have been caused by the virus. But in 1987, the dead dolphins began washing up in South Carolina in late fall, then the numbers spiked again in March 1988, according to a NOAA report.

More than 10,000 dolphins are thought to roam the Southeast coast; the coastal numbers in South Carolina-Georgia have been estimated between 6,000 and 7,000.

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