Human parainfluenza viruses (HPIVs) are the pathogens that primarily affect young children; in whom the viruses cause upper and lower respiratory tract infections. The nomenclature and taxonomic relationship of HPIVs have changed consider-ably over the last decade. These are now composed of five sero-types: HPIV-1, HPIV-2, HPIV-3, HPIV-4a, and HPIV-4b. They belong to two different genera: the genus Respirovirus (HPIV-1, HPIV-3) and the genus Rubulavirus (HPIV-2, HPIV-4a, and HPIV-4b).
Human parainfluenza viruses (HPIVs) show following features:
· HPIVs are pleomorphic viruses measuring 150–200 nm in diameter.
· The virus contains a single-stranded, nonsegmented, nega-tive-sense RNA genome with nucleoproteins P and L. It is surrounded by a helical nucleocapsid, which contains glyco-protein spikes.
· The surface spikes consist of H, N (neuraminidase), and F proteins. Both H and N proteins are present on the same spike, whereas the F protein is present on a separate spike. The F protein mediates the formation of multinucleated giant cell.
Viral replication of the parainfluenza viruses is similar to that of measles virus.
The virus contains five serotypes: HPIV-1, HPIV-2, HPIV-3, HPIV-4a, and HPIV-4b. These serotypes show cross-reactions among themselves.
Human parainfluenza viruses grow in primary monkey kidney (PMK) cells (Rhesus and African green monkeys). The virus also grows in continuous monkey kidney cell lines (LLC-MK2), which is excellent for continuous passage and almost as good as PMK cells for primary isolation.