Getting rid of the cat smells

[John Franczyk]

I've seen a number of posts on BR about houses that have bad aromas from trash, dead animals, etc., but I haven't found the best advice yet on getting rid of cat smells.  Here's the situation:

3 BR 1 bath SFR in western New York. The house was built in 1975. Stereotypical eccentric cat lady/widow has lived there for 20+ years. At least 4 cats have lived in the house with her at all times, and any number of feral cats come and go at will because she left lots of food out for them. I did not last more than a few minutes in the house before gagging from the aroma. My first thought is that the house needs to be gutted and rebuilt because that's the only way to get rid of the pervasive aroma of cat urine and ammonia. The kitchen and bath need to be updated, and gutting the rest of the house might be the best solution.

Are there any viable alternatives to a complete gut job here?

Thanks for any advice.