Transmission electron microscopic (TEM) image revealed the presence of numerous intracellular paramyxovirus nucleocapsids, which in this instance, were responsible for a case of the mumps. Paramyxoviruses are members of the family, Paramyxoviridae, and those that cause mumps in humans belong to the genus, Rubulavirus. The virus itself can present itself in a number of morphologic shapes, including spherical, and stand-like, or filamentous. At its core lies a non-segmented, negative-sense RNA genome. A member of the genus Rubulavirus, the mumps virus is the pathogen responsible for causing mumps in human beings, with an average incubation period of 16 to 18 days, and ranging between 12 to 25 days. Mumps can be prevented with MMR (measles-mumps-rubella) vaccine. MMR vaccine prevents most, but not all, cases of mumps and complications caused by the disease. Two doses of the vaccine are 88% (range: 66-95%) effective at preventing mumps; one dose is 78% (range: 49%-92%) effective.