This symptom is caused by a mite, not an infection, so fortunately it's not a disease. These types of mites are very common on a variety of trees, and their feeding activity creates these minor tissue deformities called galls. While an eyesore, they don't cause serious harm to the tree and can be ignored. Raking-up the leaves this autumn might help to reduce the mite population for a future year, but it's not necessary or a guarantee that the mites won't reappear again in a future year. You can learn more about mite galls in the linked Ohio State article.

Miri