Doctors please give your opinion - Does the body's immune system and it's status play a large role in scabies?

The immune system really doesn't do much for scabies since it is on the skin, not inside you. You are over thinking the immune system here. Yes, permethrin is the treatment. However, single lesions just on the elbows does not sound like scabies, and sleeping on the floor is not usual for transmission. It is possible you have a contact dermatitis from the floor. Is this a new place or your original place? If new, also consider fleas, mosquitos.