Over 300 dolphins have washed up along the eastern coast of the U.S. since July 1st of this year. Scientists at the NOAA declared a Unusual Mortality Event, allowing them to use fund and perform an extensive investigation of the cause. A combination of classic of tissue investigation along with molecular techniques that assayed for the presence of the virus, revealed the cause to be a Morbillivirus. The Morbillivirus family includes viruses such as measles, that infects humans, and distemper, that infects dogs. The dolphin virus poses no threat to humans.
A similar outbreak in 1987 killed more 700 dolphins. This recent outbreak was probably caused by a large enough population of young, susceptible dolphins being being to now sustain another epidemic of the disease. The virus is likely to continue to cause illness until the population of susceptible individuals declines, either by them gaining immunity to the virus or dying.