Panel 42. The mumps virus is a large, enveloped virus, more or less spherical, about 1/8000th of a millimeter in diameter. Its envelope is relatively fragile. The photograph at the bottom shows a burst virus, revealing its capsid with helical symmetry. This virus infects the salivary glands located between the upper jaw and the ears. The infl ammation of these glands causes ear pain and diffi culty opening the mouth to talk or eat.