It would seem that the Riftbrand can manifest itself in the most innocuous mushroom and be passed on if the contaminated fungus is ingested. The Marsh Hog in the area have a habit of rooting up a particular Black Fungi while they forage and I suspect that they are the source of the illness. You can find the Shiny Black Fungi all over Aughmand but they mostly tend to spring up in dark and wet patches of dirt. Return any that you find to me and we may be able to slow the spread of the Riftbrand among the Marsh Hogs.