Not sure if this is possible but how about an infected or half undead class?
- Can only eat rotting flesh
- murky water doesn't cause dysentery
- Never gets a wellness bonus
- Damage to body/limbs reduced by 1/2, damage to head x2 damage
- Infected animals won't attack unless player attacks
- Constantly smells
- Undead strength does x3 melee damage
- Extra stamina
- Reduced run speed
Something along those lines.