Dragon-Pox is a disease that occurs in wizarding homes. It is like our chickenpox in its effects. However, dragonpox can kill a elderly wizard, as happens to Abraxas Malfoy. (The death was mentioned in Harry Potter and the Half-blood Prince.) Another person to contract dragon pox is Elphias Doge, who had contracted the disease before going to Hogwarts, and it left his face pockmarked and greenish, and as a result people tended to avoid him.