How Do Pet Dogs and Cats Get Worms
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How Do Pet Dogs and Cats Get Worms

How do pet cats get worms, how do pet dogs get worms? How to diagnose worms in a pet, how to treat worms in a cat or dog. How do pets get heartworm? How to protect a pet from getting worms. Learn the different ways that pets get worms. Worms are internal parasites that can make pets sick and increase feeding costs.

Our pet cats and dogs, as well as other animals, are often plagued with parasites. Internal worms can be a real problem, and if neglected can cause health problems, even death.

Knowing how our cats, or dogs. get worms is important in preventing these internal parasites.

There are many different types of worms and each is slightly different in terms of how our pets get them.


Heartworm is more of a problem in dogs, but does occur in cats too. Heartworm is fatal when enough worms build up in a dogs heart. Heartworm is spread via mosquitoes. The mosquito takes blood from an infected animal, sucking up tiny eggs or larval worms in the blood it drinks – these are then transferred to the next dog where they begin to grow and eventually live in the heart muscle.


It is interesting to know pets with fleas can get tapeworms from eating the fleas when they itch using their mouth they actually end up swallowing fleas, the fleas can carry tape worm eggs.

Mutual Grooming

Tapeworms can be transferred through grooming, as tiny segments of tape worm often cling to the fur around an animals anus or on their tail.


Eating another animals stool (coprophagia) is another way animals can come into contact with tapeworms and most other worms. Quite simply put an animal who has worms may shed some, or shed some worm eggs in their stool. This behavior is more common in dogs than in cats.

Eating Grass

Once the stool has broken down, or even been cleaned up, there still may be some worm eggs in the environment. These eggs can be dormant for months. Very small worm larva move up stalks of grass. This is one way rabbits, sheep, and other grazing animals come into contact with worms, however dogs, and cats, who eat grass will also find themselves eating tiny worms which will grow once inside a host animal.

Filthy Yards

When owners do not keep their yards clean greatly increase their pets chances of re-infesting itself with worms. As well this will attract flies, which can result in the deadly concern known as “Fly Strike”, a problem with maggots, not worms..

From their Mother

If a mother cat, or dog, has worms, she will very likely pass worms on to her kittens or pups.

Eating an Animal with Worms

Cats, or dogs, who eat wild animals are very likely to get worms. Worms are common in mice, gophers, birds, and pretty much any animal a cat, or dog, might eat.

Uncooked Meat

Pork is of particularly concern as it may contain worms.

cats outside

photo by author

How to Know if a Cat or Dog has Worms

You may notice the pet is eating a lot, but not gaining weight, it may have a bloated appearance, and will always be hungry (this can also be a problem when pets are fed low quality diets). You may notice diarrhea, particularly if it has blood in it. Worms may be noticed in the stool, or in heavy cases pets may vomit worms.  Lethargy and excessive shedding are also symptoms of a heavy worm infestation.

Heartworm can be suspected if a dog is coughing after exercise, and seems not to have a normal amount of energy for its age and breed.

What to do if a Cat or Dog has Worms

There are many kinds of worms and worming products do not treat all kinds of worms. Therefore taking a stool sample to the veterinarian is important to determine what kind of worms a pet has (even if no worms can be seen in the stool, there may be eggs).

Once the kind of worms are known treatment can take place.

Again owners need to be aware that over the counter wormer is not always effective against all types of worms.

Keeping a clean yard will also reduce our pets chances of contacting worms, and always cleaning up after our pet is important. Cats can have their risk reduced if kept in a proper outdoor cat enclosure. Proper flea medication (again not over the counter flea medication – which has been linked to pet deaths) should be used only if fleas are known to be active.

Before any animal is to be bred, it should be wormed.

Pets who go outdoors should be wormed regularly, in some cases this may mean every six months.  Prevention measures should be taken against heartworm in dogs through a vaccination program.

Further Reading

Flea Medications Linked to Pet Deaths

Fly Strike - Flies Kill Pets

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Comments (13)

Good to know . . .

Very informative. I didn't know that fleas could carry tapeworms... I've seen dogs itch themselves with their teeth... I always thought that they might be born with worms.... I took some classes in animal science, but didn't ever get to worms and stuff.. I just did the anatomy before changing direction in my education.

Great advise for dog and cat owners. Heart worm has only just come to light so to speak in the Uk, but here as we have no mosquitoes it would seem it is spread by frogs, slugs and snails and is a different kind of worm to the one your have mentioned but this heart worm to can cause serious damage and even death. Big thumbs up for your warning about buying over the counter worm treatments, they just don't work.

Curious, Lisa, how does the frog play into this scenario?

I don't know much about the UK heart worm James but there are posters going up in Vet surgeries, pet stores etc I think the worm eggs are passed to the dogs when the dogs plays with or eats the frogs, slugs or snails or the worms are carried via the slime! A dog walker I know told me that her vet had told her that even if one of the involved climbed over your dogs toys in the garden there was a chance the dog would pick up heart worm, so the slime seems likely! I think I am at the vets tomorrow, I will ask:-)

Ranked #21 in Pet Health

An excellent informative article, Brenda. I suppose animals gain worms the way we do, through hands and mouth by way of contaminated food and other ways.

for the record there are at least 30 Species of Mosquito in the UK only about 1/4 of them bite people.. the rest feed on animals- such as dogs.. thus spreading the heartworm. Heartworm exist as tiny organisms in the blood stream - and must be injested by a mosquito then put into another animal where they grow and make their way to the heart.

Great advice for my cats, thanks Brenda.

wow... never knew we had them here Brenda, I have never seen one, we have little midges and they nip some people! This is great information, how do you get rid of them? I suppose it is blood test rather than faecal samples to determine if they have them?

Doh, I must be having a blond week! It is not even heart worm but lung worm that is carried by snails and slugs! and I don't think frogs even come into it LOL but I can't sure! good job we have you Brenda x

to Lisa. Getting rid of heartworm is tricky, not all dogs survive the treatment, it depends how early it is caught, they are injected with medicine to kill the worms, but as the worms are in the dogs heart the dog must be kept rested so the dying worms dont become lodged. As such prevention is always better.

Nasty, thank goodness they are not common here.

Thank you. Now I will know what to look for, luckily none of my dogs have ever gotten worms.