The family of Paramyxoviridae contains viruses that induce a wide range of distinct clinical illnesses in humans.
These include measles virus, which in rare instances is followed by subacute sclerosing panencephalitis (SSPE); mumps virus, which has symptoms of parotitis, orchitis and encephalitis, and the parainfluenza viruses which are respiratory pathogens.
Virions are enveloped and enclose a helical nucleocapsid containing single-stranded RNA.
Most virions are roughly spherical (about 200nm in diameter) but they can be much larger and more pleomorphic.
The virus envelope is a lipid bilayer, studded with virus encoded glycoproteins which have properties of haemagglutination and fusion (the F protein).
By transmission electron microscopy, and negative staining, the helical ribonucleo-protein capsid has a "herring-bone" appearance.