If you are using standard sized foundation, you will need to take steps to keep the Varroa under control. There are many options. Apistan being the least useful one since the mites are all pretty much resistant to it now. I have not used Terramycin since 1976.
No you don't have to medicate them, but you will have to do something to control Varroa. The only 100% natural thing I've found is to use natural or small cell size (buy 4.9mm foundation or stop using foundation and use some kind of comb guide). http://www.bushfarms.com/beesnaturalcell.htmhttp://www.bushfarms.com/beesfoundationless.htm
Assuming you haven't done that and assuming you don't really want to medicate with hard chemcals, then powdered sugar, thymol products (apilife var etc.) or oxalic acid would be a good plan.http://www.bushfarms.com/beespests.htm#varroahttp://www.bushfarms.com/beespests.htm
If you don't see other problems then Varroa would be my only concern.