Can you get rid of fleas if cat visits another house?

[NeurologicallySpeaking]

Cats have caught fleas- over a decade of cat ownership and this has never happened.

Have Indorexed the house multiple times and hoovered /washed everything. Treated the cats repeatedly with Prinovox from vet plus a one off tablet. They still have fleas! One visits another house daily - I have asked them not to let him in but they ignore me. Their house must have fleas (if it didn't already it will do now!) but they are not treating it so every day he visits he will bring them back.

He is an outdoor cat and will not be kept in.

Vet seems to think the drugs will kick in eventually but it has been 6 weeks now ...

None of my cats over the years had fleas, apart from a kitten I took in. She was covered in them, but I dealt with them immediately and thankfully, they didn't spread to my other 2 cats. Years later, I've taken in 4 strays, 3 of which I've deflead and wormed regularly. The 4th most recent cat addition, quite young, who didn't have fleas when he first arrived, (confirmed by vet), has suddenly acquired them. I've now treated him, washed everything, but he's still scratching & 1 of the other cats has started scratching as well😾. I think they're coming from a stray that's started to come inside when I'm not around. I don't know what the answer is, if they're continually catching them other untreated cats Here's the little carrier

I thought being on the prescription drops would stop them catching them- ie flea from another cat or house would bite them but just die and not start the breeding cycle. It is very weird.

If they're getting treated properly for fleas then it shouldn't matter where they go, any fleas that jump on them will die. I don't know that the treatment is you mentioned, but any decent monthly spot on (Endectrid/Advantage/Advocate/Stronghold) should do the trick.

You would be surprised how insidious flea build up in the house is. I didn't realise I had a flea infestation until I saw some jumping on the stairs which apparently is the final stage before armageddon.
I had the entire house smoke bombed by a professional and the cats have had monthly flea treatments ever since - and no problems at all.

See I wouldn't mind paying for an exterminator to fumigate the house but if they are going to bring back fleas from the other house they are visiting then not sure what the point is.

It is a monthly spot on - Prinovox which is the same as Advocate