Members of the family Paramyxoviridae are pleomorphic enveloped viruses that contain a single-stranded, non-segmented RNA genome of 13-19 kilobases (Lamb and Parks, 2007). These viruses have been isolated from many species of avian, terrestrial and aquatic animals around the world. Some members of the family Paramyxoviridae are well known human (measles, mumps, respiratory syncytial virus and various human parainfluenza viruses) and animal (rinderpest virus, canine distemper virus and Newcastle disease virus [NDV]) pathogens, while the pathogenic potential of many others is still unknown. The family is divided into two subfamilies, Paramyxovirinae and Pneumovirinae. Subfamily Paramyxovirinae is further divided into five genera: Rubulavirus, Respirovirus, Henipavirus, Morbillivirus and Avulavirus. Subfamily Pneumovirinae is divided into two genera: Pneumovirus and Metapneumovirus (Mayo, 2002).