We live in the Shawnee National Forest. Most of our 3 acres trees are hickory with a few oak here and there. We noticed some "pimples" on the leaves of one of our hickory trees that has a branch that hangs onto our deck. To me they look like pimples but when squashed, nothing comes out of them. It does not appear to be on any other trees in the yard. Is this something that could spread? Is it dangerous to the forest or people?