Virus named as culprit in dolphin die-off
Officials confirmed Tuesday that morbillivirus, a virus similar to measles, is the culprit in the death of more than 300 dolphins along the East Coast in recent weeks. It is the same virus that killed off more than 700 dolphins between 1987 and 1988.
As of Aug. 25, 333 bottlenose dolphins have turned up dead or nearly dead along beaches from New York to North Carolina. Scientists call such cases "strandings." Virginia has seen the most deaths, with a total of 174. The virus causes substantial weight loss as well as oral and skin lesions.
There have also been many reports of floating carcasses that have not been recovered, National Oceanic and Atmospheric Administration (NOAA) officials said in a Tuesday conference call. This means the number of animals that have died is likely higher than currently reported.
It is difficult to estimate the overall mortality rate, they noted, because there is no way of testing entire populations to see how many dolphins are infected.
It was originally thought that the die-off was limited to the region from New York to Virginia. But the number of dolphin strandings in North Carolina increased in August, to a total of 42 -- more than four times the annual average from the previous five years.
Veterinary pathologists in four states have scrambled to determine the cause of the outbreak throughout the summer. In arriving at the morbillivirus diagnosis, pathologists have used a combination of histopathology (tissue samples) and diagnostic techniques that include testing lesions that formed along the infected dolphins' brains, lungs, and lymph nodes.
The data accounts for deaths since July 1, but scientists now believe the first cases began turning up as early as February or March. Of 33 dolphins tested this summer, 32 came back confirmed or suspected positive for morbillivirus.
"We are now calling this a morbillivirus outbreak confirmed from New York to Virginia," said Dr. Teri Rowles of the NOAA Fisheries Marine Mammal Health and Stranding Response Program.
"In North Carolina we've tested four cases north of Cape Hatteras and those have tested as suspect positive for morbillivirus," she added. One carcass tested south of Cape Hatteras came up negative for the virus.
It's believed that the timing of the outbreak and the age of the dolphins are also important factors, Rowles added.
"Many of the dolphins younger than 26 years old have limited to no immunity to this virus," she explained, because the last time the virus broke out, they weren't born yet. So now, "they don't have the initial antibodies to protect them from the morbillivirus."
The researchers ruled out influenza and several other viruses as they narrowed it down to morbillivirus. They are still determining if there are other environmental or immunological factors that are leaving the dolphins more susceptible to the virus.
While the virus is deadly among animal populations, it is not a threat to humans and does not spread easily between species.
"Humans have their own morbillivirus, which is measles, but this virus has never been shown to be infective to people and it is unlikely that it would happen," said Dr. Jerry Saliki of the University of Georgia.
Knowing what caused the 1987-88 die-off allowed researchers to narrow the investigation more quickly. But it will not necessarily help save any dolphins -- the only way for the dolphins to escape the outbreak is to develop antibodies, which takes time. The current outbreak could last into the spring of 2014.
"As the outbreak proceeds, the number of immune animals will increase, gets to a point that will mimic natural vaccination," said Saliki. Once immune, they will "no longer become sick or die or get stranded. That's how it eventually peters out."
