Quick note about illness in general: if you do adventurer things (swimming, climbing, hiking, fighting), your HT (or whatever) rolls to resist are at -2 or your Encumbrance level while doing those adventurer things, whichever is worse. If you stay indoors and do nothing but sleep, sip soup, and get up to use the porcelain god, you get +1.
Histoplasmosis (Spelunker's Lung)Histoplasmosis, or spelunker’s lung, is an infection that comes from a fungus that grows in soil mixed with bird or bat droppings. As such, it is common in caves where bats dwell. Since nobody ever heard of a roleplaying game in an underground labyrinth with lots of bat guano, this should be a seldseen disease. It is quite common in the Ohio River Valley but happens throughout the world. To rouse the spores, something needs to disturb the soil.
Patients with histoplasmosis will have a fever and a cough, as the spores get into the lungs. The pain someone who has lost more than a third of his hit points will feel will be in his chest, and maybe a headache. Harsher cases of histoplasmosis can turn into serious lung problems.
Statistics: Respiratory (from the spores of a fungus that grows in bat or bird droppings); HT to resist. 3d+1 day delay; 1 point toxic damage; 12-hour cycle with 12 cycles. Symptoms include coughing and moderate pain (p. B428) after the loss of 1/3 HP, and severe pain (p. B428) after the loss of 2/3 HP. Not contagious.
D&D 3.5e: Inhaled, DC 15, Incubation 3d6+1 days; Damage 1d2 Con.