Human parainfluenza viruses (HPIVs) are the viruses that cause human parainfluenza. HPIVs are a group of four distinct single-stranded RNA viruses belonging to the Paramyxoviridae family. There are four types of parainfluenza virus, all of which can cause upper respiratory infections or lower respiratory infections (pneumonia) in adults and children. The hemagglutinin-neuraminidase (HN) is involved with viral attachment and thus hemadsorption and hemagglutination.