Section 8 Tenant

I have a Section 8 Tenant that has a rat issue. I have had this renatal property for 5 years and have not had a rat problem until the new tenant moved in. Within 3 months of the lease, the house has rats. I have been to the property 3 times and noticed how nasty the house has got. I noticed pizza crust in the closet and chicken bones on the floor. I have discussed the importance of keeping a clean house. How should I address the rat issues and the importance of keeping a clean house. Am I responsible for getting rid of the rats?