Bed Bugs in Rental Apartments

I purchased multiple condos in an apartment complex. There were already tenants in the property when they were purchased. I allowed them to stay and renewed their leases. I now have a tenant that has bed bugs in their unit. As the landlord am I liable to pay for the bed bug treatment? They could have been there before I purchased the property or the tenant could have brought them in there. Will this treatment cure the problem even though they could be in the walls and coming from other units? If they want to move into another unit will the bed bugs just follow them to another unit and cause a bigger problem for me?
This is in the state of Arizona.
Any help is appreciated.