Well I haven;t done any programming since using Fortran77 in 1990, but it would be cool to create some new diseases with real side effects.
Eg. with leprosy you lose nerve sensation which causes you to be more proe to injury, so first you lose fingers (lower Dex), toes (Agi), and then limbs.
If you get hit really hard in the head you can fracture your ethmoid bone causing you to lose your sense of smell (Gas immunity) but also making you prone to meningitis infection (brain crushed my swelling and you die)
You could aspirate vomit (from drinking too much, or poisoning, or head injury) and get pneumonia causing you do become exhasuted very easily and making you weak and less agile, less end.
Tuberculosis would be a good disease (and likely) you could catch it from orcs and zombies and other humanoids (if they had it) but its very infective so you could pass it on. It would cause, exhaustion, muscle wasting (progressive weakness) less AGI and End. And could be fatal.
You could add some basic nutrition disease too. they would be very appropriate. Eg. don;t eat enough red meat - you get anemia (exhausted), dont eat enough fruit you get scurvy, don;t drink enough fluids get dehydated, eat spoiled food get diarrhea, and vomiting, casuing dehydration and starvation.
I could come up with a bunch more.