Quarantines have been used since Biblical times to separate the sick from the well (mostly lepers--cool disease to study, but not to have), but the term comes from the Latin word for forty. 14th century Venice required incoming ships to hang out in their harbor for forty days to avoid bringing plague into the city.
Plague? I LOVE plague!
(Again, cool to study, not to have).
You have no idea how thrilled I am to write about bubonic plague in my current WIP- fleas, festering buboes, and bodies piled in towers. Yay!
That said, I think I need someone to quarantine me. I'm currently a walking petri dish--I've threatened my students with coughing all over them if they don't act like angels this week. So far they've complied, mostly because I look like walking death.