I've noticed quite a bit of it coming thru the sale ring earlier in the year. And I've had some cases in my calves this year plus on a couple cows. First I can remember ever having myself. So as stated it is a fungus. I found a product at a product at Tractor Supply (active ingredient is Benzalkonium Cloride 0.15%) in a 32 oz. squirt bottle (Fung-a-way). I can treat the cows in the pasture, just throw a bag of cubes out and ready, aim, squirt. Calves I had to be a little sneakier or pen.
Oh, it can go away on it's own too, but it might get worse before it does. Only took a couple "treatments" for mine.