Eggs or fungus
First off, just in case, that is poison ivy so don't handle it.
What you are seeing is actually a leaf gall, caused by a tiny, tiny mite called an eriophyid mite. Galls are just tissue swelling and this one is the Poison Ivy Leaf Gall Mite.
Compare to here: https://www.marylandbiodiversity.com/viewSpecies.php?species=10426
They are not of great concern.