An Unusual Encounter: Mysterious Skin Reaction After Beggar's Touch

This morning, while I was about to sit down with a Coke at a small roadside spot, a beggar approached me. He was persistent, so I told him to move along. As I turned to walk to my table, he touched my elbow with two fingers. About an hour later, I noticed two spots on my skin, and seven hours later, they had grown larger and felt like they were burning, almost like acid. I've never experienced anything like this before, and I have no idea what it could be. Take a look at the photo.