A die-off of bottlenose dolphins that began in June has been steadily moving south as herds of the marine mammals migrate south, they said.
The virus, which has killed 753 dolphins so far -- in the worst outbreak ever recorded -- has now been identified in two species of whale, NBC News reported Monday.
Three stranded and decaying humpback whales and two pygmy whales in similar shape tested positive for the dolphin morbillivirus, researches said.
The National Oceanographic and Atmospheric Administration says more tests will be needed to see if the dolphin virus, usually rare in whales, was the cause of their deaths.
"Most of them are very decomposed," making detection of the disease in tissue samples harder, Teri Rowles of the NOAA Fishers Marine Mammal Stranding Response Program said.
Resident Florida bottlenose dolphins are at risk of catching the virus, which spreads through close contact or shared air, she said.
"There is no vaccine that can be deployed for a large bottlenose dolphin population or any cetacean species," Rowles said. "Currently there is nothing that can be done to prevent the infection spreading, or prevent animals that get infected from having severe clinical disease."