Have been to the vet today because I have 8 cats and usually the flea problem is completely under control, but this last month or so they are all starting to scratch even after treatment (Frontline Combo).
Vet says it is not possible to become 'immune' to Frontline, and has given me a long helpsheet. It says it can take between 1 and 3 months to get rid of fles completely once they have really got hold, and by the time you see them or get bitten yourself, they really have got hold.
They are not just on your cat, they are in your soft furnishings, laying eggs which in turn will become new fleas.
Helpsheet recommends frequent combing, vaccuuming (of the house, not the cat), and also says the Frontline you can buy at the supermarket or pet shop is not the same as Frontline Combo (but then I suppose they would say that, wouldn't they?).
It also says there is no point keeping a cat out of a recently vaccuumed room in the hope that you will keep fleas out - if the cat has been treated it is best to let it wander everywhere because it will then hoover up fleas (who prefer to be on it, rather than in th carpet etc where there is no food) and kill them.
Right, thorough treatment and combing of 8 cats will take place tonight. 7 will be happy about it, 1 will involve 3 people, a very large towel, a pair of heavy-duty gauntlets and possibly a trip to A&E 