Viral Characteristics of HPIV - Pleomorphic virus i.e. the ability to change morphology and biologic functions of host cells - Single-stranded, nonsegmented, negative-sense RNA genome with nucleoprotein P and L proteins - Diameter is 150-300 nm - RNA genome contains 15,000-16,000 nucleotide organized to encode at least 6 common structural proteins - Rule of 6; According to advanced genetics, HPIV undergoes most efficient viral replication and transcription when genome is divisible by 6. - F and HN are the glycoproteins which are very important in the pathogenesis of HPIV