Thousands of Baikal seals in Lake Baikal, in a region of the former Soviet Union, later in 1987.
About 17,000 harbor seals in northwestern Europe in 1988.
Thousands of striped dolphins in the Mediterranean in 1990-91.
A wave of bottlenose dolphins in the Gulf of Mexico in 1993-94.
The viruses that struck the Mediterranean striped dolphins and European harbor porpoises were different from the seal viruses, researchers said. Both types were found among the Atlantic bottlenose dolphins; in fact, some animals had been infected by both.
A different morbillivirus causes human measles. Others cause distemper in dogs and sicken cows, sheep and goats.
The diseases vary, but in general they affect the lungs, brain, intestinal tract or lymphoid tissue, said Lt. Col. Thomas Lipscomb, chief of veterinary pathology for the Armed Forces Institute of Pathology and a researcher on marine morbilliviruses.
Morbilliviruses are identified under the microscope by tiny abnormalities in tissues. Researchers were able to identify them in marine mammals with the help of a new laboratory technique for analysing RNA (ribonucleic acid).
Morbilliviruses ``tend to cause severe diseases that are often fatal,'' Lipscomb said.
In America, where children are immunized against measles, deaths are rare. But in some undeveloped countries, Lipscomb said, ``measles often has a fatality rate of about 20 percent.''