A Brief Overview Of Morbilliviral Epizootics In Aquatic Mammals     Thomas P. Lipscomb   Armed Forces Institute of Pathology, Washington, DC     Prior to 1987, morbilliviral infection was unknown in aquatic mammals.  Since 1987, tens of thousands of seals and dolphins have died during seven well-documented morbilliviral epizootics that occurred in coastal or inland waters of three continents.  Bottlenose dolphins (Tursiops truncatus), Baikal seals (Phoca sibirica), harbor seals (Phoca vitulina), gray seals (Halichoerus grypus), striped dolphins (Stenella coeruleoalba), common dolphins (Delphinus delphis ponticus), and Caspian seals (Phoca caspica) were affected by these outbreaks.  Fatal morbilliviral disease has also been diagnosed in harbor porpoises (Phocoena phocoena) and pilot whales (Globicephala melas).  The Baikal and Caspian seal epizootics were caused by canine distemper virus, the harbor and gray seal epizootics by the newly recognized phocine distemper virus, and the dolphin, porpoise and pilot whale cases by the newly recognized cetacean morbilliviruses (porpoise morbillivirus, dolphin morbillivirus and pilot whale morbillivirus).  Serologic studies have shown that morbilliviral infection is widespread in many pinniped and cetacean species.  Harp seals (Phoca groenlandica) and pilot whales have high incidences of seropositivity consistent with enzootic infection and may cause epizootics through contact with susceptible species.  Factors that cause changes in distribution of aquatic mammal species, such as climate change, may be an underlying cause of the recent series of epizootics.