First, I'm an idiot, when I posted a little about disease previously, I didn't realize that the Blackmoor digest has a table with more info on the very next page! My only excuse is that I was in a rush to prepare for the session and was reading it in pdf so it wasn't as obvious.
Unfortunately, it didn't matter because the table didn't answer some of those questions I had anyway. In fact, the one thing the text was clear on, chance of catching the disease, the table contradicts-- 90% vs 1%. The only way I can understand this is that the lower number applies to player characters and the higher to anyone else once pcs are infected. But that's a guess, it doesn't say that.
Ok, establishing that, no, those rules aren't going to help me as written, let's forge on.
Different Rules for Sieges
Disease may be a perfect example of how you might want different mechanics for different subsystems in a game. What I realized looking at the rules in Blackmoor is that much of the subject is seen through the lens of sieges and armies. Which makes sense, descending from Chainmail, if you're fighting with massed forces it would be nice to have some rules for how disease would spread through the ranks and weaken those forces by attrition.
But those concerns are different from my concerns in dealing with an adventuring party. I think you might need at least slightly different rules for the two situations.
Disease and Your Character
Let's think about how a disease affects pcs. It can't be immediately fatal or it becomes identical to a poison. Once contracted a lot of real diseases take about 12 days, almost two weeks, to fully manifest themselves.
What about symptoms? Some fantasy diseases have odd symptoms, but with natural diseases catching it usually means you're weakened severely or bed-ridden. So if we are going to have mechanics for diseases that are reminiscent of real diseases the character:
- contracts it or not
- for a few weeks is probably too weak to adventure
- might die if not cured in those weeks
Does Disease Matter?
If a party is far from civilisation or help, this could lead to some dramatic tension, especially if the disease is spreading through the party. But I think that would the rare case. Cure disease is available to 5th level clerics in most old school rules systems (6th for Moldvay). So, unless your campaign world has few of that level cleric around, disease becomes an minor inconvenience, a money sink.
Well, unless the possibility of the city being infected mentioned above, is the party's home base settlement. That could cause drama, adventure hooks, and provide an even bigger money sink. So, is the only reason to mess with non-fantastic diseases at the party level to spread it to their base of operations?
Some diseases would allow for characters to be carriers (think Typhoid Mary) and this would make the likelihood of them spreading the disease to cities and troops much higher. But on the other hand, it would make it much less likely for players to realize that they are, in fact, the spreaders of the pestilence. And that would make it hard to engage the drama and hooks mentioned above if players don't feel responsible.
Scars and the Aftermath
Some diseases can leave permanent scars or effects (think small pox). It is possible that a cure disease will save a players life without preventing these. So disease might become more frightening if it could permanently reduce a character's charisma (as Blackmoor suggests), blind them, or leave some other mark. But I have a hard time believing a holy person could lay on hands, curing a sickness and still leave these marks of the sickness. Maybe. I suppose it's how miraculous you conceive the divine magic in your campaign.