1 Lambert: Oooh... I don't feel well...
1 Kyros: A sorceror must have put a curse on you.
2 Mordekai: Don't be ridiculous. It's caused by evil spirits.
2 Alvissa: No, it's an imbalance of the bodily humours.
3 Draak: Draak folk say sick made by bugs too small to see with eye.
4 Lambert: Heh, very funny, Draak. This is why your race is known for its amusing primitive beliefs...

As first observed by that great reptile-man scientist, Antonie van Lizardhoek.

---

2018-11-13 Rerun commentary: One interesting approach to disease and contagion in a fantasy fiction or gaming world is to make diseases not be caused by bacteria and viruses, but instead they really are caused by curses, evil spirits, imbalances of bodily humours, misalignments of the planets, comets, etc. There are no such things as germs. If a real life doctor was transported into the fantasy realm, they'd be flummoxed - their microscope would show nothing, and modern day treatments based on antibiotic properties wouldn't work.

To actually cure someone, you'd need a cleric or a sorcerer or a wise village elder herbalist. Or even perhaps a druid or an astrologer.

There's no need to assume that the physical and biological laws of a fantasy world are anything like those that exist in our own world. Using the beliefs of ancient societies and treating them as true is one good way to make your world truly fantastical.