# Are Roundworms in Cats Contagious to Dogs? Yes, roundworms in cats can be contagious to dogs, but not in the simple way most owners imagine. A cat with roundworms will not pass them to your dog through a sneeze, a shared water bowl, or a friendly nose-to-nose greeting. The real risk sits in the environment, specifically in soil and surfaces contaminated by infected feces. Because dogs and cats share some of the same roundworm species, a dog can pick up an infection from a yard a cat has used. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Roundworms are common intestinal parasites in both dogs and cats, especially in young animals [1]. - Cats and dogs share at least one roundworm species, Toxascaris leonina, so cross-species infection is possible [1][2]. - The usual route is indirect. A dog swallows infective roundworm eggs from soil, grass, or objects contaminated by infected feces [3]. - Direct cat-to-dog transmission through casual contact is not the main concern. Contaminated environments are. - All dogs and cats should be treated preventively for roundworms, and feces should be picked up promptly [3][1]. ## What Roundworms Are in Plain Words Roundworms are long, tube-shaped worms that live in the small intestine of dogs and cats [3][1]. They are cream-colored and can range from about 3 to 15 centimeters long, depending on the species [1]. They do not attach to the intestinal wall. They live in the gut and absorb nutrients from the food your pet eats [4]. Two roundworm species infect dogs, Toxocara canis and Toxascaris leonina [1]. Cats are infected by Toxocara cati and Toxascaris leonina, plus a third species found in parts of eastern Asia [1]. That shared species, T. leonina, is one reason a cat's roundworms can matter to your dog. Roundworms are among the most common intestinal parasites of cats, affecting roughly 25% to 75% of cats, with higher rates in kittens [4]. They are also common in dogs, particularly puppies [1]. If you have both species in one home, you are dealing with a parasite that thrives when hygiene slips. ## Are Roundworms in Cats Contagious to Dogs? This is the question most multi-pet owners ask, and the honest answer has two parts. First, a cat cannot give your dog roundworms by touching it, sleeping near it, or sharing a food bowl. The infectious stage of roundworm is not the adult worm. It is the egg, and those eggs must develop in the environment before they can infect anyone [4]. Second, your dog can absolutely become infected from a space your cat has contaminated. Adult female roundworms shed fertile eggs in the infected cat's feces [4]. Those eggs need several days to several weeks in the soil to reach the infective larval stage [4]. Once they do, a dog that sniffs, licks, or eats contaminated soil or grass can swallow them [3]. So the practical takeaway is this. Your cat is not directly contagious to your dog in the way a respiratory virus would be. Your cat's feces, and the soil around it, can be a source of infection for your dog. There is one more layer. Dogs can also get roundworms by eating a rodent that is already infected [3]. In a multi-pet home with a yard, that adds another route that has nothing to do with your cat. ## Signs Owners Notice Many infected pets show no symptoms at all [3]. That surprises owners, but it is common. When signs do appear, they tend to be more obvious in puppies and kittens [3][1]. Watch for: - A potbellied or bloated look, especially in young pets - Mucoid diarrhea or loose stool [1] - Weight loss or poor condition despite eating [1] - Worms in the stool or vomit, which look like thin spaghetti [3] - A dull coat or reduced energy In heavy infections, larvae migrate through the intestines, liver, and lungs before maturing [3]. That migration can cause coughing or breathing changes in puppies. If your dog or cat seems to be losing weight or has ongoing diarrhea, a fecal test is the fastest way to sort out what is going on. ## Causes and Risk Factors Roundworm infection comes from a few main sources. **Ingesting infective eggs.** This is the big one for both species. Eggs come from feces-contaminated soil and other contaminated objects [3]. They are sticky and durable, and they can survive in the environment for a long time. **Eating an infected rodent.** Dogs can become infected this way [3]. **Mother-to-offspring transmission.** Puppies can get roundworms from their mother before birth and while nursing [3]. Kittens can also be infected through their mother's milk, which is why young animals carry such a heavy parasite burden. **Shared outdoor space.** If your cat uses the yard or a litter box that gets emptied into the yard, your dog is exposed to the same soil. This is the core of the roundworms in cats contagious to dogs issue. Risk factors that raise the odds include young age, access to the outdoors, crowded or shelter environments, and poor fecal cleanup. A study of dogs and cats in Dhaka City found an overall parasite prevalence of 63.33% in dogs and 58.37% in cats, with Toxocara species the most commonly identified parasite in both [5]. Another study in Portugal found Toxocara canis in 14.9% of dogs sampled [6]. These numbers show how widespread these worms are, and why routine prevention matters even in homes that look clean. ## How It Is Diagnosed Diagnosis is usually simple. Your veterinarian examines a stool sample under a microscope to look for roundworm eggs [3][1]. This is called a fecal flotation, and it is the standard first step. Owners sometimes spot adult worms in stool or vomit first [3]. If you see them, save a sample in a sealed bag and bring it in. Do not handle worms with bare hands, and wash up afterward. In some cases, your veterinarian may use antigen testing or molecular tools to identify the exact species [1][2]. Species identification matters because it helps clarify the transmission risk in a multi-pet home. A newer multiplex PCR test can identify T. canis, T. cati, and T. leonina specifically [2]. Not every clinic offers this, and it is not always necessary, but it can be useful in complex cases. ## Treatment Options Treatment is effective and widely available. Multiple deworming drugs are approved with activity against roundworms [1]. Your veterinarian will choose the product and calculate the dose based on your pet's weight, age, and health status. Never guess a dose or split a product meant for another animal. A few practical points: - Treat all pets in the home, not just the one with confirmed worms. Roundworms move easily between animals through a shared environment. - Follow the retreatment schedule your veterinarian gives you. Dewormers kill adult worms, but they do not kill eggs that are still developing in the soil [4]. A second treatment clears worms that were larvae at the time of the first dose. - Do not use a dog product on a cat or a cat product on a dog unless your veterinarian specifically says it is safe. Some ingredients are toxic to the wrong species. - If you are treating a cat, see [Roundworm Treatment For Cats](/knowledge/veterinary-medicine/parasitic-diseases/roundworm-treatment-for-cats) for a species-specific overview. For dogs, [Roundworms in Dogs: Zoonotic Risk Deworming and Puppy Schedule](/knowledge/veterinary-medicine/parasite-control/roundworms-in-dogs-zoonotic-risk-deworming-and-puppy-schedule) covers the puppy schedule and zoonotic angle. If you want more detail on safe product choices, [Roundworm Treatment for Cats: Safe Dewormers and Prevention](/knowledge/veterinary-medicine/parasitic-diseases/roundworm-medicine-for-cats) walks through what to look for. ## Recovery, Outlook, and Long-Term Management Most pets recover fully after appropriate deworming. The outlook is good when treatment is completed and reinfection is prevented. The catch is that reinfection is easy if the environment stays contaminated. Here is a simple comparison to help you think about the two species. | Feature | Cats | Dogs | |---|---|---| | Main roundworm species | Toxocara cati, Toxascaris leonina [1] | Toxocara canis, Toxascaris leonina [1] | | Shared species | Yes, T. leonina [1][2] | Yes, T. leonina [1][2] | | Common infection route | Eggs from contaminated soil, mother's milk [4] | Eggs from soil, infected rodents, mother before birth and nursing [3] | | Zoonotic risk | Yes, T. cati is zoonotic [1] | Yes, T. canis is zoonotic [1] | | Best prevention | Routine deworming, prompt feces disposal [3][1] | Routine deworming, prompt feces disposal [3][1] | Long-term management in a multi-pet home means treating deworming as a household routine, not a one-time fix. Your veterinarian will set a schedule based on your pets' ages, lifestyles, and risk factors. Pets that go outside, hunt, or live with young children usually need closer monitoring. ## Prevention in a Multi-Pet Home Prevention is where you have the most control. These steps reduce the parasite load in your home and yard. **Pick up feces promptly.** This is the single most effective habit. Roundworm eggs need days to weeks in the soil to become infective [4]. Removing feces before that happens breaks the cycle. Scoop litter boxes daily and pick up dog waste immediately. **Deworm on a schedule.** All dogs and cats should be treated preventively [1]. Your veterinarian sets the frequency. Puppies and kittens need more frequent treatment than adults. **Cover sandboxes and manage the yard.** Cats often use sandboxes and garden beds as litter areas. Cover sandboxes when not in use, and keep dogs away from areas where cats defecate. **Wash hands after handling pets, soil, or waste.** Roundworm eggs can infect people who accidentally swallow them, and young children are at higher risk because they put objects in their mouths while playing outside [3]. This is the same zoonotic concern covered in [Roundworms in Cats: Toxocara cati and Human Larva Migrans Risk](/knowledge/veterinary-medicine/parasite-control/roundworms-in-cats-toxocara-cati-and-human-larva-migrans-risk). **Control rodents.** Since dogs can get roundworms by eating infected rodents [3], rodent control in and around the home lowers risk. **Keep new pets separated until checked.** A new kitten or puppy should have a fecal test and deworming before free access to the rest of the household. **Do not assume a clean-looking pet is parasite-free.** Many infected pets show no signs [3]. Routine fecal testing catches infections you cannot see. ## Limitations and When to Contact a Veterinarian This article covers general principles. Your pet's individual case needs a veterinarian who can examine the animal, review its history, and run appropriate tests. Contact your veterinarian the same day if: - You see worms in your pet's stool or vomit - Your pet has diarrhea lasting more than a day or two - Your pet is losing weight despite a normal appetite - A puppy or kitten has a bloated belly, poor growth, or coughing Seek emergency care now if: - Your pet is vomiting repeatedly and cannot keep water down - Your pet is lethargic, weak, or collapsing - A young pet has severe diarrhea with blood or dehydration Call for a routine visit if: - You have a new pet and no fecal test has been done - You need a deworming schedule for a multi-pet home - You are unsure whether a product is safe for both your cat and your dog If you suspect a pet swallowed a medication meant for the other species, call your veterinarian or a pet poison control hotline right away. Do not wait for symptoms. ## Frequently Asked Questions ### Can my dog get roundworms from my cat's litter box? Yes, indirectly. If infected cat feces or contaminated litter ends up in soil your dog can reach, your dog can swallow infective eggs from that soil [3][4]. The eggs need time to develop in the environment before they become infective, so daily litter scooping and prompt disposal reduce the risk a lot [4]. ### Do I need to treat my dog if only my cat has roundworms? Yes, treating every pet in the home is the standard approach. Roundworms are common in both species, and a shared environment means exposure is likely even if your dog tests negative today [1]. Your veterinarian will confirm the right products and schedule for each animal. ### Can roundworms spread between dogs and cats through grooming or shared bowls? Not through grooming or shared bowls directly. The infectious form is the egg, which must develop in soil or another contaminated surface before it can infect a new host [4]. Direct contact between pets is not the main transmission route. ### How long do roundworm eggs survive in my yard? Roundworm eggs are hardy and can remain in the environment for a long time, which is why prompt feces removal matters so much [3][4]. There is no simple home test to tell you when a yard is clear. Keeping up with cleanup and deworming is the practical answer. ### Can I get roundworms from my cat or dog? Yes. Toxocara canis and Toxocara cati are zoonotic, meaning they can infect people [1]. Human infection happens when someone accidentally swallows an infective egg from contaminated soil or an object, and young children are at higher risk [3]. Hand washing and prompt waste cleanup are your best protection. ## Related Articles - [Roundworm Treatment For Cats](/knowledge/veterinary-medicine/parasitic-diseases/roundworm-treatment-for-cats) - [Ringworm In Cats](/knowledge/veterinary-medicine/parasitic-diseases/ringworm-in-cats) - [Roundworm Treatment for Cats: Safe Dewormers and Prevention](/knowledge/veterinary-medicine/parasitic-diseases/roundworm-medicine-for-cats) - [Roundworms in Dogs: Zoonotic Risk Deworming and Puppy Schedule](/knowledge/veterinary-medicine/parasite-control/roundworms-in-dogs-zoonotic-risk-deworming-and-puppy-schedule) - [Roundworms in Cats: Toxocara cati and Human Larva Migrans Risk](/knowledge/veterinary-medicine/parasite-control/roundworms-in-cats-toxocara-cati-and-human-larva-migrans-risk) - [How To Tell If A Dog Has Roundworms Or Hookworms](/knowledge/veterinary-medicine/parasitic-diseases/how-to-tell-if-a-dog-has-roundworms-or-hookworms) - [Are Cat Worms Contagious to Other Cats? What Owners Should Know](/knowledge/veterinary-medicine/parasitic-diseases/are-cat-worms-contagious) - [Are Dog Worms Contagious to Other Pets and People?](/knowledge/veterinary-medicine/parasitic-diseases/dog-worms-contagious) - [Are Whipworms in Cats Contagious? What Owners Should Know](/knowledge/veterinary-medicine/parasitic-diseases/whipworms-in-cats-contagious) - [Toxocara cati Roundworm Infection in Cats and Kittens: Prenatal Transmission and Clinical Management](/knowledge/parasites/pet-parasites/toxocara-cati-roundworm-cats-kittens-prenatal-transmission) - [Intestinal Parasites in Dogs and Cats: Zoonotic Potential and Public Health Considerations](/knowledge/parasites/pet-parasites/intestinal-parasites-dogs-cats-zoonotic) ## References 1. [Roundworms in Small Animals - Digestive System](https://www.merckvetmanual.com/digestive-system/gastrointestinal-parasites-of-small-animals/roundworms-in-small-animals). Merck Veterinary Manual. 2. [Development of a novel multiplex PCR assay for the specific identification of Toxocara canis, Toxocara cati and Toxascaris leonine in dogs and cats](https://pubmed.ncbi.nlm.nih.gov/41747541/). Veterinary parasitology, 2026. 3. [Roundworms](https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-topics/roundworms). Cornell University College of Veterinary Medicine. 4. [Gastrointestinal Parasites of Cats](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/gastrointestinal-parasites-cats). Cornell University College of Veterinary Medicine. 5. [Prevalence, risk factors, and zoonotic implications of gastrointestinal parasites in dogs and cats in Dhaka City, Bangladesh](https://pubmed.ncbi.nlm.nih.gov/41242795/). Veterinary parasitology, regional studies and reports, 2025. 6. [Beyond the clinical eye: mapping intestinal parasitic infections and its risk factors among dogs and cats across Portugal](https://pubmed.ncbi.nlm.nih.gov/42459543/). Frontiers in veterinary science, 2026. ## Further Reading - [Merck Veterinary Manual: Dog Owners](https://www.merckvetmanual.com/dog-owners) - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)