Infections You Can Catch From Pets, and the Ones You Cannot

People are told to get rid of the cat far more often than the evidence supports. The advice usually arrives at a pregnancy or a cancer diagnosis, it is well meant, and it is almost always unnecessary.

Infections do pass between pets and people. The list is shorter than the anxiety suggests, the routes are specific, and nearly all of them are managed by handling rather than by rehoming.

The ones that are actually transmitted

What passes from pets to people, and how

Infection	From	How it actually reaches you
Toxoplasmosis	Cats, but mostly food	Cat feces after 24 hours, soil, and undercooked meat
Cat scratch disease	Cats, via their fleas	A scratch or bite from an infected cat
Salmonella	Reptiles, amphibians, poultry, chicks	Handling the animal or anything in its enclosure
Ringworm	Cats, dogs, rodents	Direct contact with the coat or skin
Campylobacter and giardia	Puppies and kittens with diarrhea	Contact with feces, usually via hands
Psittacosis	Birds, especially parrots	Breathing dust from droppings in an enclosed space
Bite infections	Cats and dogs	The bite itself; see animal and human bites

The first row is the one that causes the most unnecessary distress. Most human toxoplasmosis in the United States comes from undercooked meat and unwashed produce, not from cats — and an indoor cat fed commercial food is a negligible source.

The toxoplasmosis conversation, properly

A cat sheds the parasite for a short period after a first infection, usually early in life, and the shed form is not infectious for roughly the first day. That single fact is what makes daily litter changing effective.

• Have someone else change the litter tray if you are pregnant or immunosuppressed
• If that is not possible, change it daily, wear gloves, and wash your hands after
• Keep cats indoors and feed commercial food rather than raw meat
• Wear gloves for gardening, since outdoor soil is a more likely source
• Cook meat to a measured temperature and wash produce; see food safety when your immune system is weak
• Do not adopt a new stray kitten during pregnancy or immune suppression

Scratches, bites and the flea connection

Cat scratch disease produces a small bump at the site and swollen lymph nodes a week or two later. In healthy people it usually settles by itself; in immunosuppressed people it can be more serious and is treated.

Cat bites are a different matter and are covered in our article on animal and human bites. They infect more often than dog bites because the teeth are narrow and deep, and a cat bite over a joint or tendon is a same-day problem.

Reptiles, amphibians and birds

This is the one genuine reason to reconsider a pet rather than a habit. Reptiles, amphibians, chicks and ducklings carry salmonella routinely, and it is on their skin and everything in the enclosure rather than only in their droppings.

• Not recommended in households with children under five, adults over 65, or anyone immunosuppressed
• Wash hands thoroughly after any contact with the animal or its enclosure
• Never clean a tank in the kitchen sink, or in the bath
• Keep the animal out of food preparation areas entirely
• Do not kiss or hold reptiles near your face
• Birds: clean cages in a ventilated space and dampen droppings first to avoid dust

Choosing a pet while immunosuppressed

Getting a new animal is a different question from keeping an existing one, and it is reasonable to be more careful about it.

• An adult animal from a known home carries less risk than a young stray
• Kittens and puppies shed more organisms and are more likely to scratch and nip
• Avoid animals with diarrhea entirely until a vet has dealt with it
• Keep the animal current on veterinary care, deworming and flea control
• Feed commercial food rather than raw diets, which carry salmonella into the house
• Tell your veterinarian that someone in the household is immunosuppressed; it changes their advice too

Dogs, specifically

Dogs generate less of this anxiety than cats and deserve a short mention of their own. The realistic risks are bites, which are covered in our article on animal and human bites, diarrheal organisms from puppies, and ringworm.

The one genuinely dog-specific caution is licking. A bacterium carried in dog saliva can cause severe infection in people without a working spleen or with significant liver disease — rare, but serious enough that those groups are advised to avoid letting dogs lick broken skin, and to seek care promptly after any bite.

Fish tanks, farms and the unusual ones

Two exposures come up rarely and are worth a line each, because neither is obvious.

Aquarium water can carry an organism that causes a slowly growing skin infection on the hands and forearms, typically after a scratch while cleaning a tank. It is easily missed for months because it looks like an ordinary lump and does not respond to ordinary antibiotics. Wearing gloves prevents it; mentioning the aquarium is what gets it diagnosed.

Farm animal contact, including petting zoos and county fairs, is a recognized source of E. coli and cryptosporidium, particularly in children. Hand washing stations exist at those events for a reason and hand sanitizer is not an adequate substitute against cryptosporidium.

What pets do not transmit

Some of the most common worries are simply not how these infections work.

• MRSA passes in both directions between people and pets, but people are usually the source
• Colds and flu are not caught from dogs or cats
• Lyme disease is not caught from a dog; the dog can bring ticks indoors, which is a different problem — see tick bites in Georgia
• Worms from pets are uncommon in adults with basic hygiene, and routine deworming handles most of it
• HIV and hepatitis are not transmitted by pets in any direction

Pets also do measurable good for the people who live with them, which belongs in the calculation. If you are immunosuppressed and worried about a specific animal or a specific exposure, that is a much better question to bring to an appointment than a general one. Our article on what happens at an infectious disease consultation covers how to raise it, and you can reach us through the contact page.

Frequently asked questions