Fleas in rental property!? Who is responsible

[Nick Hundertmark]

Please read entire scenario before responding. One of my rentals is a semi-detached home where I own one side. It’s rented to a good tenant who pays on time and keeps the place clean. The house next door was recently sold to an owner occupant who has several large dogs. My tenant has brought to my attention that there’s a full blown flea infestation occurring in the house. It’s unlikely that the fleas came from her. She hasn’t recently bought used furniture or clothing and she doesn’t interact with or own any pets. We are assuming right now that the fleas are coming from the neighbor, as they share a back yard. I’m going to find out for sure by talking with the neighbor, but right now let’s assume that’s where the fleas are coming from. If that’s the case, who is responsible? My lease says that the tenant is responsible for flea and pests control related costs that occur during her occupancy. I don’t want to screw her over though because she’s a good person. Even if I were to pay or help cover the cost of remediation in the home, it would likely re-occur due to source being the neighbor. We could treat the house and put a fence in the backyard to keep the dog off the grass. Even that may result in a reoccurrence as fleas can probably migrate that short distance or possibly find a way through the walls. What would you do? Is the neighbor liable for any of this? Thanks you, Nick