From Wikipedia:
“The earliest known written account of mumps was in the 5th century B.C. by Greek physician Hippocrates. He described an outbreak of mumps on the island of Thasos in approximately 410 B.C. and provided a fuller description of the disease in Corpus Hippocraticum in Epidemics. In 1934, the etiology of the disease, the mumps virus, was discovered by Claude D. Johnson and Ernest William Goodpasture. They found that rhesus macaques exposed to saliva taken from humans in the early stages of the disease developed mumps. Furthermore, they showed that mumps could then be transferred to children via filtered and sterilized, bacteria-less preparations of macerated monkey parotid tissue, showing that it was a viral disease.
The word “mumps” is first attested circa 1600 and is the plural form of “mump”, meaning “grimace”, originally a verb meaning “to whine or mutter like a beggar”. The disease was likely called mumps in reference to the swelling caused by mumps (parotitis), reflecting its impact on facial expressions as well as its causing of painful, difficult swallowing. “Mumps” was also used starting from the 17th century to mean “a fit of melancholy, sullenness, silent displeasure”.”