"Mumps" is called "Mumps" in German too. Got it as a child. Wasn't fun!
It's an infectious disease caused by the mumps virus.
The disease is also commonly known as "mumps", due to the characteristic facial swelling.
The Japanese common name literally reads as "fat cheeks woman fever". The English one comes from the grimace-looking expression ("mumps") it causes.
Hey...!
Why didn't you tell us sooner!?
You dunderhead...!