What your dog and cat can actually pass to you

By Nora Penn

Less than the internet implies, but not nothing. Three parasites genuinely cross from pets to people — and none of them travel by affection. They travel by faeces left sitting in soil, sand or a litter tray. Here is the honest list, how each one actually reaches you, and the short routine that removes most of the risk.

What can actually pass from a pet to you

The honest list is short. Most of what lives in a dog or cat stays in a dog or cat — but three things genuinely cross over, and they cross over in completely different ways.

Parasite	How it reaches you	Who's most at risk
Roundworm (Toxocara)	Swallowing eggs from soil that pet faeces sat in	Young children playing in dirt or sand
Hookworm (zoonotic)	Larvae burrow through bare skin	Bare feet or bare skin on contaminated soil or sand
Toxoplasma	Faeces left in the litter box for days, or undercooked meat	Pregnancy and weakened immune systems

Notice that none of them come from stroking your dog. They come from faeces that has been sitting somewhere. That single fact is what makes prevention so straightforward.

Roundworm: the one that matters for children

Toxocara is the dog and cat roundworm, and the human illness it causes is called toxocariasis. Adult worms live in the pet's gut; eggs pass out in faeces and sit in soil, where they take time to become infective.

People don't catch it from the animal directly — they catch it from the ground. CDC notes that severe cases are more likely in young children who have been playing in, or eating, contaminated dirt. Sandpits and unfenced garden beds are the classic settings.

Which is why the prevention advice is unglamorous and effective: have a vet test and treat your dogs and cats, wash hands after handling pet waste, and teach children that eating dirt or soil is not safe. Clean up after your dog promptly — eggs need time in the environment before they can do anything.

Hookworm: the one that goes through skin

This one surprises people, because there is no swallowing involved at all.

The exposure is the ground your own animal has used, or somewhere other animals have. CDC describes infection occurring when larvae burrow into unprotected skin from soil or sand contaminated by animal faeces — a garden corner the dog favours, or a shaded patch under a deck, does it as readily as a beach.

The reassuring part: most people who are infected recover without treatment. The larvae are in the wrong host and can't complete their life cycle in a person. Shoes and a towel between skin and sand handle most of the risk.

Toxoplasma: the cat one, and why daily scooping works

This is the one that generates the most anxiety in pregnancy, and it's also the one where the timing detail matters most.

Cats are the only definitive host — the parasite can complete its sexual cycle nowhere else. Unsporulated oocysts are shed in the cat's faeces, usually for one to three weeks. Freshly shed, they cannot infect anyone.

Two other routes worth knowing, because cats get more blame than they deserve: undercooked meat and contaminated soil are also significant sources — and CDC advises against feeding cats raw or undercooked meat, and wearing gloves for gardening.

If you're pregnant and someone else can change the litter tray, that's the simplest answer. If not, gloves, daily changes and hand-washing get you most of the way there.

What doesn't pass to you

Worth stating plainly, because the internet blurs this badly:

• Heartworm. Spread by the bite of a mosquito, not by your dog. It's a serious canine disease and it is prevented rather than easily treated — but it isn't something your dog gives you.
• Whipworm. The dog species doesn't establish in people the way Toxocara and hookworm larvae do.
• Tapeworm from fleas. A dog swallows an infected flea while grooming. Human cases exist but are rare, and they require swallowing a flea — not petting the dog.

So the mental model is: your risk is about faeces in the environment, not about affection.

Testing: how often, and what it costs

Guessing is as unhelpful in pets as it is in people. The veterinary standard is specific:

Testing can be done through your vet, or with a mail-in fecal kit that ships a sample to a lab. Either route answers the same question: which parasite, if any — because the treatment depends entirely on the answer.

Treatment: what's over the counter and what isn't

This split matters, and most pages skate over it.

• Available without a prescription in the US for the common intestinal worms — fenbendazole, praziquantel and pyrantel pamoate, plus some combination products. Quad Dewormer, for instance, is sold over the counter and covers tapeworms, roundworms, hookworms and whipworms in a single dose. Not every combination is: Drontal Plus, with a similar mix, is prescription-only — and pyrantel on its own is not FDA-approved for cats.
• Prescription only: heartworm, both ways. FDA notes that many products are approved to prevent heartworm in dogs and all of them require a veterinarian's prescription, and the only approved treatment for an established infection is melarsomine, an arsenic-containing drug given by deep injection. There is no safe over-the-counter route here.
• Match the drug to the parasite. A dewormer that clears roundworm may do nothing for tapeworm. This is exactly why the fecal test comes first.

Puppies and kittens are dewormed on a schedule from a young age as standard practice — that one is a conversation with your vet, not a purchase decision.

The routine that does most of the work

• Pick up faeces promptly — in the garden and on walks. Eggs need time in soil to become infective, so removing them early breaks the chain.
• Change the litter box daily, and wear gloves if you're pregnant or immunocompromised.
• Wash hands after handling animals, litter or pet waste, and before eating.
• Cover sandpits when not in use, and keep children from eating soil.
• Shoes on where dogs have been, especially on beaches and in parks.
• Don't feed raw meat to cats, and cook meat properly for yourself.
• Test on schedule rather than deworming blindly — over-using dewormers drives resistance.

Common questions

Can I catch worms from my dog licking me?
That isn't the route the crossover parasites use. Roundworm needs eggs swallowed from soil, and hookworm needs larvae burrowing through skin from contaminated ground. Both require faeces that has been sitting in the environment.

Do I have to rehome my cat if I'm pregnant?
No. The parasite doesn't become infectious for one to five days after shedding, so daily litter changes remove it before it can infect anyone. If someone else can do the litter tray, better still.

How often should my pet be tested?
Four times in the first year, then at least twice a year for a healthy adult — more if they travel, hunt, or spend a lot of time outdoors.

Can I just deworm regularly and skip testing?
You can buy some dewormers over the counter, but a product that clears one worm may not touch another, and routine over-use drives resistance. Testing tells you which one you're treating.

My dog has fleas — can I get a tapeworm?
It's possible but rare, and it requires swallowing an infected flea. Treating the fleas treats the cause.