The virus that has killed nearly 800 bottlenose dolphins off the East Coast of the United States has turned up in four whales that have washed ashore, a potentially troubling development if it is shown to be the cause of their deaths, a U.S. government marine expert said Thursday.
But it is too early to know whether cetacean morbillivirus killed three humpback whales and one pygmy sperm whale that have stranded since July 1 between the U.S. states of Massachusetts and Georgia, said Teri Rowles, director of the marine mammal health and stranding response program for the National Oceanic and Atmospheric Administration’s fisheries service. A fourth humpback whale was too decomposed to allow reliable testing and results are not yet available on two other pygmy sperm whales, she said.
The humpback population has rebounded, but the species is still listed as endangered.
“There are too many unknowns right now,” Rowles said. “We would be concerned if indeed there is an outbreak of this virus in humpback whales causing clinical disease and mortality.” Sometimes, she said, a marine population can carry a virus without it causing widespread harm.
There have been 14 humpback strandings — when dead or dying animals wash ashore — along the East Coast this year, double the six-year average of seven, she said. While that, too, is cause for concern, the total number is small. A network of stranding responders will continue to monitor the situation, she said.
Tests on a stranded common dolphin, a spotted dolphin and a harp seal did not reveal the presence of the virus, she said.
The die-off of bottlenose dolphins continues at an unprecedented pace, Rowles said. Between July 1 and Sunday, 782 have died, already surpassing the 740 dead in 1987 and 1988, during the last big outbreak of morbillivirus.
Generally, the virus causes death by suppressing the dolphin’s immune system, leaving it vulnerable to pneumonia and other infections. It poses no threat to people, despite its similarity to the measles virus, and there is nothing officials can do to protect dolphins in the wild.
Officials are beginning to see dolphins wash ashore in Florida as the cetaceans migrate south to warmer water but haven’t included them in the total because tests have not yet conclusively linked the deaths to the virus.
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