Free Table FGM037a: d30 Fantasy Diseases
This table is just a list of 30 Fantasy Diseases, along with the minor and major symptoms of each malady. There are no "rules" to get in the way of the GM using this at their table, and it my assumption that the GM will use whatever their rules use for communicability, vectors, duration, severity, etc.
Now I do like the current edition of HackMaster's rules for diseases and will probably end up having to add some stats to my personal-use diseases table, but I know that would be too much for a lot of GMs.
Click on the lead-in graphic above, or use this link to go to the listing on DTRPG.