A tiny mite has infested humans for at least 2,500 years. It is often hard to detect, and causes a fierce, itchy skin condition known as scabies. Dermatologists estimate that more than 300 million cases of scabies occur worldwide every year. The condition can strike anyone of any race or age, regardless of personal hygiene. But there is good news: with better detection methods and treatments, scabies need not cause more than temporary distress.