There is no medical treatment for acarine. Some varroa treatments (eg: apiguard) have been found to be beneficial but it would be illegal to use them for treating acarine.
Requeen. A good prolific young queen will have more brood. As mites can only infest so many bees the % gets smaller in a big colony.
Select prolific queens with lots of brood to breed from.
Good grooming traits.
Avoid robbing and drifting.
Avoid swarms and absconding – feral colonies can cause issues.
A brood break can help – as mites can only infest bees 0-5 – older bees impervious.
Ensure good food supply.
(This would indicate this as something that overcrowding in an area could cause)