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Each year from 2007 to 2012, somewhere between 300-400 bottlenose dolphins were found stranded along Atlantic shores from New York to South Carolina. In 2013, that number tripled to more than 1,300.

But why? 

As is often the case with unusual mortality events, many potential causes of the outbreak are initially investigated. Through testing at the UC Davis One Health Institute’s Marine Ecosystem Health Diagnostic Surveillance Laboratory, and confirmed by three other laboratories in the US and through pathology findings, the cause of the dolphin deaths was determined to be associated with an outbreak of Dolphin Morbillivirus.

Morbilliviruses are in the family Paramyxoviridae and specific morbilliviruses cause measles in people and canine distemper in dogs.

To date, more than 90% of the 100 dolphins tested were positive for the virus, which causes skin lesions, damage to the lungs and infections in the brain of dolphins. 

Detecting the Outbreak

Electron micrograph showing dolphin morbillivirus viral particles in the cell culture from an infected bottlenose dolphin tissue. Photo: S. Fish, California Animal Health and Food Safety (CAHFS) Laboratory System. 

Electron micrograph showing dolphin morbillivirus viral particles in the cell culture from an infected bottlenose dolphin tissue. Photo: S. Fish, California Animal Health and Food Safety (CAHFS) Laboratory System. 

Around late July the unusual mortality event caught the attention of the National Oceanic and Atmospheric Administration (NOAA), which quickly organized a Cetacean Morbillivirus and Epidemiology Team that includes members of the Marine Mammal Health and Stranding Response Program, of which the One Health Institute’s lab is a member.    

By July 29, samples collected from the stranded dolphins began arriving at UC Davis. Within one week of testing for a variety of potential causes, the lab informed NOAA about the positive tests for the morbillivirus. Similar announcements came from partnering university labs in the days that followed, confirming the results. Now nearly all of the samples are coming directly to UC Davis for testing for the virus.

Moving Forward

“We were able to isolate the virus in culture so are now in the process of sequencing the whole viral genome,” said Dr. Tracey Goldstein, Director of the laboratory at the One Health Institute. “We are hoping to  learn more about the virus, such as why this virus is so virulent. We would also like to understand more about how this virus is transmitted, how long an animal can shed the virus and how it is maintained in the population.

NOAA has created an interactive map of the dolphin strandings so that you can measure them by date, location and more.

NOAA has created an interactive map of the dolphin strandings so that you can measure them by date, location and more.

According to NOAA, morbillivirus spreads “through inhalation of respiratory particles or direct contact between animals,” but the fact that dolphins live in the ocean makes the transmission of the virus a bit more mysterious.

Back in 1987-88, more than 740 dolphins died in a similar outbreak off the US east coast as far north as New Jersey and as far south as Florida. The current outbreak appears to be traveling south down the same coast, with Virginia experiencing the highest number of strandings to date.

“As samples come in from a new state, we are confirming the presence of the virus to confirm that it is indeed moving down the coast” said Goldstein.

Meanwhile, NOAA says its work is ongoing: “Further evaluations will continue over the next several months as new animals are found or new evidence determines the direction of the investigation. These rigorous investigations may take several more months to complete.” Read the whole NOAA announcement.

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