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Do indoor cats have fewer parasites?

Are indoor or outdoor cats less likely to have parasites? Dr. Lee discusses research showing indoor cats have fewer parasites.

Do indoor cats have fewer parasites?

Q: I have an autoimmune disease that requires me to take potent immunosuppressive drugs. I have two indoor-outdoor cats and wonder whether it would be healthier for me if I kept them indoors. In other words, can they bring in diseases from the outside that are dangerous to me?

A: Yes. Recent research found that cats allowed to venture outdoors are 2.8 times more likely to be infected with parasites than indoor-only cats. Some of these parasites can infect humans, so your health is likely to be better if you restrict your cats to your home.

Two intestinal parasites, roundworms and hookworms, are widespread. Their eggs are microscopic, so you won’t spot them on your hands after you pet your cats or scoop the litter box. If you inadvertently ingest them, you could suffer blindness, seizures or organ damage.

Fortunately, your veterinarian can prescribe a liquid you apply to each cat’s skin monthly to kill these worms, along with fleas and other parasites.

Unfortunately, though, some parasites are not so easily foiled. The recent report, actually an analysis of 21 studies that examined the prevalence of 19 feline parasites, identified additional nasty organisms, including Toxoplasma and Bartonella.

Toxoplasma is a protozoan parasite that causes severe disease in people with compromised immune systems. Bartonella bacteria cause cat scratch disease in humans.

Moreover, infected pet cats can transmit disease to wildlife. For example, domestic cats with the feline immunodeficiency virus have spread it to mountain lions. Pet cats with the too-common panleukopenia virus that causes respiratory and eye infections have infected panthers.

Lee Pickett, V.M.D. practices companion animal medicine. Contact her at

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