So, I came back yesterday from an attempt to hunt wild boar (found tons of tracks, no boar this time). And today I discovered that, despite my best efforts, I've acquired numerous itchy mosquito bites. It then dawned on me that despite spending almost all their time outside in the elements, Hearthlings never get mosquito bites!
Perhaps this could be some kind of randomly occurring short-lived wound? And if left untreated, it could fester into malaria!