The National Oceanic and Atmospheric Administration (NOAA) announced that a measles-like virus is responsible for hundreds of bottlenose dolphin strandings along the mid-Atlantic coast this summer.
Since early July, unusually high numbers of dead or dying bottlenose dolphins have washed ashore from New York to North Carolina. About 155 dolphins strand in the mid-Atlantic from January to late August during a normal year, but this year almost 500 dolphins washed ashore in the same time period. The sudden increase prompted NOAA to declare an Unusual Mortality Event for bottlenose dolphins.
The suspected culprit is cetacean morbillivirus—a virus in the same family as human measles and canine distemper. Both whales and dolphins are susceptible to different variations of the virus, which are collectively called cetacean morbillivirus. The disease is usually spread within a species through inhalation of respiratory particles or by direct contact between animals. Sick dolphins develop pneumonia, skin lesions, and brain infections, eventually washing ashore dead or dying. Morbillivirus is not always fatal—some individuals fight off the disease and produce antibodies that protect them from subsequent infections.
Officials tested more than two-dozen of the recently stranded dolphins for cetacean morbillivirus, and all were infected with the disease. But the virus might not be the only disease contributing to the strandings. Researchers also found Brucella bacteria—which causes brucellosis in humans, cattle, and marine mammals—in the lesions of four tested dolphins.
Morbillivirus caused a similar mid-Atlantic die off from 1987-1988 that killed more than 740 dolphins. Officials will continue monitoring this mortality event, and you can help by contacting your local marine mammal stranding network if you find a live or dead stranded dolphin.
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