The morbilliviruses are serologically crossreactive and closely related, belonging to the family Paramyxoviridae with each species having a different host range. Before 1976, only 4 species were recognized: 1/ measles virus, (MV), 2/ rinderpest virus (RPV), 3/ peste-des-petits ruminants virus (PPRV) and 4/ CDV.

Since 1976, new morbilliviruses have been discovered which

have their own host ranges. Phocine distemper virus (PDV) infects primarily seals--pinnipeds and a second virus has been found to infect cetaceans such as dolphins (dolphin morbillivirus or DMV) and porpoises (porpoise morbillivirus or PMV).