id on leather disease

I just got back in town after being out for about 4 days and my lovely toadstool leather has four holes about half the diameter of a bic pen. My clowns host in it, but they've been doing it for a while with no problems. Three of the four holes are straight through, the other looks like it's working its way to being complete. I'm guessing a lugol's dip will be the first step, but what's causing it? I'll try to get some pictures once I finish getting settled back in tonight.
 
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