Hundreds of bottle-nosed dolphins have been dying on the East Coast, and the National Oceanic and Atmospheric Administration says a virus is likely to blame.

Morbillivirus, a disease similar to measles in humans, has been found in some beached dolphins tested by NOAA, officials announced Tuesday.

Since July 1, 333 dolphins have stranded - gotten sick and washed up on beaches, or became stuck in shallow water - between New York and North Carolina. Most of them are dying off the coast of Virginia, where 174 have stranded since July 1.

"We don't have a lot of insight as to when it will stop. Typically, outbreaks last as long as there are susceptible animals that can be infected," Dr. Teri Rowles of the NOAA Fisheries Marine Mammal Health and Stranding Response Program told reporters during a conference call.

NOAA has tested 33 beached dolphins, and 32 had either confirmed or suspected cases of the virus.

Based on a similar outbreak 26 years ago, NOAA expects dolphins will continue dying until spring 2014.

This year's dolphin die-off is the largest since a similar virus outbreak in 1987 and 1988, NOAA officials said. It's difficult to estimate how many dolphins will die, according to Dr. Lance Garrison of the NOAA Southeast Fisheries Science Center. Estimates of a 30 percent to 40 percent mortality rate in that outbreak were later found to be inaccurately high, Garrison said.

Dolphins have very little resistance to the virus, which suppresses their immune systems, NOAA officials said. The virus causes lesions on dolphins' skin, in lymph nodes, and in their brains.

There is almost no chance the virus can spread to humans, officials said, as morbillivirus strains are specific to species. Humans have their own morbillivirus -measles - and have historically not contracted morbillivirus strains from animals during outbreaks.

Still, NOAA advised swimmers with open wounds to take precautions in areas where infected dolphins have been found. With their immune systems suppressed by the virus, the sick dolphins often contract other infections that can spread to humans.

"At this point, there isn't anything we can do to stop the virus," Rowles said. "We don't have a vaccine that is developed that could be easily deployed in a wild population of bottle-nosed dolphins."