The plague: a consequence of progress

[Grothnvelth]

Let's get to it.

Rat (1) and mice (only one animal could do the trick) have long followed mankind. They have brought disease and damaged our structures. That is: Death and Destruction. VMC and BTW include many blocks that are of no natural origin. The number of such blocks could be used to measure the level of human development in a region. Therefore they could be used to spawn mice. More advanced blocks could spawn rats. (Low spawn rate but wide range for both.)(Any combination of rats and/or mice.)

Rats carry a disease (2). If they bite you, you get sick for a day or so. (Or worse.) The protection would be a vaccine. To vaccinate yourself, you must, at first, kill a rat. Get its blood.(3) (Possibly by squashing its remains in an apple juice extractor or just sticking a blade through it.) Weaken or kill the disease.[1] [2] Apply the blood to a blade (either knife or sword (in which case you are spilling guts)). And make a cut to yourself. You get a bit sick and a bonus or total immunity against the disease. [3] Many ways to screw up.

*[1] To weaken/kill the disease you could either cook the remains in a non-stoked cauldron or pour non-distilled alcohol onto the remains.
*[2] You could also sterilize the blade with distilled alcohol. If this was implemented, you get infected if you don't.
*[3] Rats and mice could damage wooden constructions and ropes. You can either kill them yourself, lay traps (if you are advanced enough to produce such contraptions) or catch them alive for your experiments (not for 20th or 21st century type experiments, more like 19th). Cheese in a hole should not work though.

Your time was squandered. I apologise for that.