Cats and Immune-Compromised People

By Jean Hofve, DVM

It’s not so unusual any more for people to have serious immune system issues. People who are taking corticosteroids or other immunosuppressive drugs, such as gold salts, cyclosporine, or azothiaprine; who have had an organ transplant; are undergoing radiation or chemotherapy; have a primary or acquired immune deficiency or other condition that impairs or suppresses the immune system; or are simply very young or very old: all need to use proper precautions if a cat is to share the home.

Unfortunately, it is still common for physicians to advise pregnant women and immune-compromised people to “get rid of the cat.” However, this is certainly not necessary. In fact, it’s been shown over and over that keeping a pet, such as a cat or dog, actually benefits the immune system by reducing stress.

There are, however, several diseases of concern that can be passed from cats to humans. We’ll look at the most common ones, and how to prevent transmission.

Toxoplasma. The most well-known zoonotic (animal-to-people transmittable) is toxoplasmosis (often simply called “toxo”), which is caused by a protozoan parasite called Toxoplasma gondii. Toxo can cause serious birth defects if the mom is infected during pregnancy; and serious illness in humans and cats with weak immune systems. Cats most often get toxo from eating infected prey or meat, but the most common sources of human infection are eating undercooked meat, especially pork; and gardening.

Toxo is shed in a cat’s feces for about three weeks after first exposure. If your cat is kept indoors, its chances of getting toxo are extremely small, although it is also possible for a cat to contract toxo from eating raw or undercooked meat.

Toxo cysts do not become infectious until about 24 hours after defecation, so keeping a very clean litterbox, and scooping once or twice a day, also reduces the risk to near zero. However, if possible, it’s best to have a non-pregnant or immune-competent person on litterbox patrol. If that’s not possible, the cleaner should wear a mask and gloves, and wash up thoroughly after scooping or cleaning.

Approximately 30% of the adult population in the U.S. has been exposed to toxo. A simple blood test (a “titer”) can determine whether or not a pregnant woman already has antibodies to toxo; if so, she is at minimal risk.

Other Protozoans. Other zoonotic protozoans include Giardia and Cryptosporidia, although it is very rare for a cat to be the source of a human infection.

Worms. Other parasites, such as roundworms and hookworms, can pose a danger to the immune-compromised individual. Fecal exams, appropriate deworming, and keeping the cat indoors will prevent these nasty little critters from endangering the guardian. Other gastrointestinal organisms can be passed in the feces, some of which can cause significant disease in people. Good litterbox hygiene and conscientious hand-washing will generally prevent disease transmission.

Bacteria. Some bacteria, like Salmonella, can infect people through contact with an infected cat’s feces. A significant proportion of dogs and cats are asymptomatic carriers. Salmonella is a common contaminant of raw or undercooked meat, and it is widespread in the environment.

In general, feeding raw meat is not recommended for pets in a household with an immune-compromised individual because of the large number of bacteria and other organisms that are usually present in raw meat. They may not affect the cat, but they can potentially be passed on to humans.

Cat Scratch Disease. This is a risk to immune-compromised individuals, and can cause a variety of syndromes in people. The organism (Bartonella) is transmitted by fleas, so keeping a flea-free home is an essential part of prevention. In addition, keeping the cat’s nails clipped, or using glue-on nail caps (Soft Claws/Soft Paws) work very well to minimize the risk from scratches.

It is unnecessary, and possibly dangerous, to declaw the cat. Declawing is not recommended by the Centers for Disease Control or by any other reputable health organization. Doctors who specifically work with HIV+ clients strongly recommend against declawing, because declawed cats will often resort to biting as a defense. The risk from a cat bite is far worse than from a scratch, because the teeth drive bacteria into deeper tissues. It is impossible to tell how any individual cat will react to this painful surgery. (For more info on declawing, see Declawing: A Rational Look, and our many other articles).

Any cat bite wound, even in people with normal immune status, requires prompt medical care.

Ringworm. Despite the name, ringworm isn’t a worm at all, but a highly infectious fungal infection of the skin. Cats can be asymptomatic carriers of ringworm, or their symptoms may look somewhat different. Typically, ringworm in cats appears on the face, feet, and ear margins, and it may look more gray and scaly than red. A cat can transmit ringworm at any time during the infection; unfortunately this includes about three weeks before symptoms start showing up! In people, ringworm typically looks like a slightly raised, reddish ring, somewhat resembling “fairy rings” in lawns. The actively growing area is on the outside edge, so topical medications should be concentrated there.

Ringworm is not usually serious except in severe cases; but it is seriously annoying due to the intense itching it causes. Keeping the cat indoors is the primary preventative, although I managed to infect myself, two adult cats, and my dog by bringing home a new kitten whose symptoms were not yet evident.


The joys of feline companionship need not be denied to anyone. With a little common sense and good hygiene practices, every home can be a happy cat home!

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