Some owners are shocked to learn that their indoor kitty caught a case of worms, but this scenario isn't unusual. Outdoor cats are more likely to pick up parasites and other infectious agents, but felines confined to the home also can ingest or inhale worm eggs.
Pests and Parasites
When it comes to parasites, your cat's predatory instinct works against him. Rodents, insects and other household pests harbor worm eggs, which are passed on to your kitty when he devours them. Mice and cockroaches are just two of the many critters that can carry roundworms eggs. Mosquitoes and ticks can transmit parasites to your pet by biting him.
Even if your kitty never goes outside, there's a good chance that members of the household come and go on a daily basis. Microscopic worm eggs can lay dormant for months, so it's easy to track them in on clothing and footwear. There's no way to avoid them completely when you are outdoors, but you can lower the chances of contamination by removing or cleaning shoes before entering the house.
From Cat to Cat
If you have both indoor and outdoor kitties, be prepared for parasites and diseases to spread between them. Your cat can pick up a case of worms by sharing a litter box or food and water bowls with an infected cat. Roundworms, tapeworms and other parasites can spread to humans, so keep children away from litter boxes and wash their hands after contact with the cat.