Mumps virus. Coloured transmission electron micrograph (TEM) of mumps virus ribonuclear protein helices (blue strands) replicating within a host cell. These helices contain the genetic material ribonucleic acid (RNA) in combination with protein. A viral particle contains a single ribonuclear protein helix enclosed in a spherical protein shell, or capsid. Mumps virus is a contagious paramyxovirus, causing swelling of the parotid salivary glands, fever, headache and vomiting. Infection can spread to the pancreas, brain and testicles. In adult males, infection can cause sterility. Magnification: x120,000 when printed 10 centimetres wide.