It’s a really good question, and one we’re asked quite often. As usual, of course, there are a couple of caveats… firstly, it does depend to some extent on the pet. And secondly, it depends how “indoors” an indoors cat is (we’ve seen people with “indoor cats” that are allowed out on special occasions before!). However, as a general rule, yes… and here’s why.
The vaccinations we recommend as routine for cats are against Panleukopenia (also known as Feline Infectious Enteritis), Cat Flu (Feline Calicivirus and Feline Herpesvirus), and Feline Leukaemia (FeLV). Now, these diseases are primarily spread cat to cat, so you might think that indoor cats would be entirely safe, but unfortunately that isn’t the case.
While the Feline Leukaemia virus breaks down rapidly in the environment, the Herpesvirus can last a day or so, the Calicivirus a month or so, and the Panleukopenia virus for over 6 months (possibly even over a year). As a result, when you come in and out of your house, there is a very real possibility that you’re bringing in active and infectious virus particles that will infect your cats – whether or not they ever go outdoors.
The only effective way to protect cats from these diseases are either by making them live in a hermetically sealed bubble (NOT good or nice for them, we think!) or by vaccination, to protect them – wherever they live.
Similar problems exist with fleas. Once in a house, fleas can lie dormant for months or years as pupae in the dust, in the carpet, or between the floorboards. However, even if they aren’t in your home (or you’ve rooted them all out!), invasion of the house by fleas being carried on vermin (mice and rats), or even on your clothing is quite possible.
Now, for most cats, the few that will enter the house this way are unlikely to be a major problem – but of course it only takes 1 pregnant flea to infest an entire house when her 3,000 or so eggs start to hatch! More of a worry, though, are those cats unlucky enough to have a flea allergy (Flea Allergic Dermatitis, or FAD). This is very common in cats, where their immune system goes into overdrive when exposed to flea saliva after a bite. Unfortunately, it only takes one bite to set them off scratching, causing self-harm and hair loss.
We think that, in general, you and your cat are both better off safe than sorry!
Cats are subject to a range of different worms – including roundworms and tapeworms. Now, it is indeed true that many cats become infected with worms by eating live prey (especially the Taeniafamily of tapeworms); so, cats who don’t hunt are at much lower risk.
And of course, mice and rats do occasionally invade even the nicest of homes, and even the gentlest of cats are prone to supplement their diet with a nice crunchy morsel if available…
However, more importantly, many cats are in fact infested with worms within a few hours of birth, which they contract through their mother’s milk. So, we must remember this possibility – of roundworms hiding away in the muscles until the cat is sick or old, and then reactivating. Even more importantly, though, the common tapeworm (Dipylidium caninum) is spread by fleas… so even one flea in the house could mean a tapeworm infestation!
Are there risks from regular preventative treatment?
Significant harm from use of appropriate medications, at the right dose, in the animals they are prescribed for, is very, very rare. However, the harm from parasitic infestations, even in indoor cats, is very much greater. On balance, then, in most indoor cats, most of the time, we strongly recommend regular preventative treatments.