Indoor cats can get worms by swallowing fleas, eating mice, or getting bit by mosquitoes that are infected, according to petMD. There are several different worm species, including tapeworms, roundworms and heartworms, that cats can contract, even without ever venturing outside the home. If worms are suspected, contact a veterinarian as soon as possible for diagnosis and treatment if necessary.
Cats often get tapeworms from infected fleas that are swallowed while they are grooming themselves. Tapeworms are readily carried by fleas and they are a common mode of transmission of worms in indoor cats. In homes where a rodent problem exists, mice that carry roundworms are sometimes caught by cats, which can lead to an infestation. Cats are natural predators, and they often hunt down mice that venture into the home. Heartworms are transmitted via mosquitoes, which can make their way indoors at various times of the year, despite one's best efforts to eliminate them.
It is important to treat any suspected incidence of worms in an indoor cat right away. To prevent worms in indoor cats, a homeowner can control fleas using flea products specifically designed for cats. Cats should be given monthly heartworm medication, and all indoor cats should be evaluated by a veterinarian regularly. Keeping an eye on a cat's waste and bringing any tapeworm segments or adult roundworms to the attention of a vet is the best way to identify and treat a worm problem.