Can you have scabies for years and not know it? my sister contracted scabies from a pupil years ago, got treated which works until she sees me and claims that i keep re-infecting her (after originally infecting me) but i never had any symptoms?

Scabies treatment: It seems very unlikely that you and your sister are continuing to share or reinfect one another with scabies. However, if you live together closely, the next time she has confirmed scabies, it would make sense for you to be treated at the same time. Also launder any shared clothing, bedding, etc at the time of treatment. If the problem continues, the two of you should see a dermatologist together.