# How Do Dogs Get Worms and Heartworm? Dogs get heartworm from the bite of an infected mosquito, not from other dogs or from dirt. Intestinal worms like roundworm, hookworm, and tapeworm reach dogs in different ways, including contaminated soil, infected feces, and fleas. Knowing how do dogs get heartworm and how they pick up other worms helps you match the right preventive to the right parasite. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Heartworm spreads only through mosquitoes. At least 70 mosquito species can carry the infective larvae [1]. - Roundworm and hookworm spread mainly through contaminated soil and feces, and puppies can get roundworm from their mother. - Tapeworm most often spreads when a dog swallows an infected flea. - Heartworm preventives do not treat intestinal worms, and dewormers for intestinal worms do not prevent heartworm. - Year-round prevention plus regular testing is the standard approach, and treatment for an established heartworm infection is costly and hard on the dog [2]. ## What These Infections Are in Plain Words Heartworm disease is a potentially fatal but preventable infection caused by a worm parasite called *Dirofilaria immitis* [1]. Mosquitoes pick up the tiny larvae, called microfilariae, from an infected animal and pass them to a new host when they bite [1]. Inside the dog, the larvae grow into adult worms over several months and settle in the blood vessels serving the heart and lungs [1]. In advanced infections, the worms move into the heart itself [1]. Adult heartworms are large. Males reach 5 to 6 inches and females reach 10 to 12 inches, and adults can survive in a dog for 5 to 7 years [3]. They start producing new microfilariae about 6 to 9 months after infection [3]. Intestinal worms are a different story. Roundworms, hookworms, and tapeworms live in the gut, and each has its own route into the body. That difference matters, because the product you use for heartworm may or may not cover the worms your dog is actually likely to meet. ## Signs Owners Notice Most heartworm-infected dogs look normal at first [4]. When signs do appear, the most common one is a cough [4]. As disease gets worse, you might see exercise intolerance, labored breathing, a swollen belly from right-sided heart failure, fainting, or weight loss and muscle wasting [4]. Intestinal worms can be quieter or messier. You may notice a dull coat, a potbelly, weight loss despite a good appetite, vomiting, diarrhea, or worms in the stool or around the rear. Some dogs show no signs at all, which is why stool checks matter. If you are trying to sort out what you are seeing, this guide on [how to tell if dog has worms or parasites](/knowledge/veterinary-medicine/parasitic-diseases/how-to-tell-if-dog-has-worms-or-parasites) walks through the common clues. ## Causes and Risk Factors ### How Do Dogs Get Heartworm? A mosquito bite is the only natural route [1]. The mosquito must first feed on an infected animal, then bite your dog. Any dog can be infected, indoor or outdoor, because all it takes is one bite from a mosquito carrying infective larvae [1]. Dogs housed outdoors face the greatest risk [1]. Geography matters too. Heartworm disease has been reported in most countries with temperate, semitropical, or tropical climates, including the United States, Canada, Australia, Latin America, and southern Europe [1]. Warm, humid areas with plenty of mosquitoes raise the odds of transmission [5]. Dogs do not pass heartworm directly to each other. They also cannot get it from soil, water, or contact with an infected dog's waste. A dog can be reinfected many times over, so different stages of infection may exist in the same animal at once [1]. ### How Do Dogs Get Hookworms? Hookworm larvae live in contaminated soil and can penetrate a dog's skin or be swallowed. Puppies can also get hookworms through their mother's milk. Because hookworms feed on blood, they can cause anemia, especially in young dogs. Hookworm is one of the reasons monthly preventives often cover more than heartworm alone. ### How Do Dogs Get Worms Like Roundworm and Tapeworm? Roundworm eggs are passed in feces and can survive in soil for a long time. Dogs get roundworm by sniffing or eating contaminated dirt, and puppies commonly get it from their mother before or shortly after birth. Tapeworm usually arrives when a dog swallows a flea carrying the tapeworm larva, which is why flea control and tapeworm control go hand in hand. Some intestinal worms can infect people too. If anyone in your home has questions about that risk, [can a human get dog worms](/knowledge/veterinary-medicine/parasitic-diseases/can-a-human-get-dog-worms) covers the household angle. ### Which Parasite Comes From Where | Parasite | Main route into the dog | Covered by typical heartworm preventive? | |---|---|---| | Heartworm | Bite from an infected mosquito [1] | Yes, that is its main job | | Roundworm | Contaminated soil, mother to puppy | Often, depending on the product | | Hookworm | Contaminated soil, skin contact, mother's milk | Often, depending on the product | | Tapeworm | Swallowing an infected flea | Usually no, needs a separate dewormer | ## How It Is Diagnosed Heartworm testing starts with a blood sample. Blood tests can detect both adult worms and microfilariae [3]. Antigen tests look for material released by adult female worms, and point-of-care tests used in clinics are highly accurate. In one evaluation, a rapid antigen test showed 98.7% sensitivity and 100% specificity compared with a reference test [6]. Microscopy can also find microfilariae in blood, and a modified Knott's test remains useful for detecting and telling microfilariae apart, particularly alongside other methods [5]. Microscopy alone can produce false positives compared with PCR testing [5]. Chest X-rays and echocardiography help show heart and lung changes once infection is confirmed [5]. Intestinal worms are usually diagnosed with a stool sample. A veterinarian floats or smears the stool and looks for eggs or worm segments under a microscope. Tapeworm segments sometimes show up as small, rice-like pieces near the tail or in the bedding, which owners often spot before any test is run. ## Treatment Options Heartworm treatment is serious medicine. Clearing an infection typically requires melarsomine, an organic arsenic compound [4]. The three-part injection series is 98% effective at killing adult worms, but dogs who do not get adequate rest afterward risk pulmonary embolisms, which can be fatal when dying worms block blood flow in the lungs [3]. Strict rest during treatment is critical to recovery [3]. For dogs that cannot receive melarsomine for another medical reason, chronic use of certain macrocyclic lactones with doxycycline has also been effective [4]. This is slower and is chosen case by case. Treatment is also expensive. A study of clinic transaction data across the United States found that treating heartworm disease is costly and often challenging, which is why preventing adult worms from developing is the mainstay of management [2]. Your veterinarian will calculate any drug dose from your dog's weight and health, and will set the rest and recheck schedule. Intestinal worms are treated with deworming medication, often given orally or by injection. The exact product and dose depend on which worm is present, your dog's weight, and your dog's overall health. Puppies usually need several rounds because reinfection and developing larvae are common. ## Recovery, Outlook, and Long-Term Management Dogs treated for heartworm can recover well, but the months around treatment are the risky part. The worms die in the pulmonary arteries, and the body has to clear them. That is why exercise restriction is not optional. A dog that runs and plays too soon after an injection can throw a clot. After treatment, your veterinarian will recheck with antigen testing to confirm the adult worms are gone. Adult heartworms can live 5 to 7 years if untreated, so follow-up testing is how you know the infection has actually cleared [3]. Intestinal worm recovery is usually faster. Signs often improve within days of deworming, though a follow-up stool check confirms the worms are gone. Dogs with heavy hookworm burdens may need time and sometimes supportive care to rebuild red blood cells. Long term, the plan is simple. Keep your dog on a preventive that matches your local risk, test on the schedule your veterinarian recommends, and control fleas. If you ever wonder whether a change in appetite, coat, or stool means worms are back, [how do I know if my dog's got worms](/knowledge/veterinary-medicine/parasitic-diseases/how-do-i-know-if-my-dog-s-got-worms) breaks down the everyday signs. ## Prevention Consistent use of preventives containing macrocyclic lactones is the foundation of heartworm prevention [4]. These products kill the larvae before they grow into adult worms, which is why timing and consistency matter more than anything else. A field trial of a monthly combination product containing milbemycin oxime and lotilaner found it effective and safe for heartworm prevention in client-owned dogs when given for six consecutive monthly treatments [7]. A few practical points: - Give the preventive on schedule, every month or as labeled. Gaps are where infections slip through. - Test before starting or restarting prevention, and test on the schedule your veterinarian sets. Blood tests detect adult worms and microfilariae [3]. - Do not assume one product covers everything. Check the label for which intestinal worms it treats, and ask your veterinarian about tapeworm coverage. - Control fleas year-round to cut the tapeworm route. - Pick up stool promptly and keep your dog away from areas with heavy dog traffic. - Ask about risk where you live. Warm, humid regions with mosquitoes carry higher transmission odds [5]. If you want a broader look at spotting worms early, [how to know if dogs got worms](/knowledge/veterinary-medicine/parasitic-diseases/how-to-know-if-dogs-got-worms) and [how to tell if dog has worms](/knowledge/veterinary-medicine/parasitic-diseases/how-to-tell-if-dog-has-worms) both cover the owner-level signs. ## Limitations and When to Contact a Veterinarian No article can tell you what is happening in your individual dog. Your veterinarian needs to examine your dog, run the right tests, and choose a product and dose based on weight and health. Contact a veterinarian the same day if you see: - A cough that does not go away, especially with tiredness or trouble breathing - Fainting or collapse - A swollen belly or sudden weight loss - Worms or rice-like segments in the stool or near the tail - Diarrhea with blood, or pale gums Go to an emergency clinic now if your dog is struggling to breathe, has blue or gray gums, or collapses and does not recover quickly. These can signal advanced heart or lung problems. Call your veterinarian for a routine visit if your dog is due for a heartworm test, has missed preventive doses, or has a new puppy that needs a deworming plan. ## Frequently Asked Questions ### Can my dog get heartworm from another dog? No. Heartworm moves from dog to dog only through a mosquito bite [1]. Direct contact, shared bowls, and shared yards do not spread it. That is why an infected dog in the neighborhood is not a direct threat, but the mosquitoes around both dogs are. ### Do indoor dogs really need heartworm prevention? Yes. Any dog, indoor or outdoor, can be infected by a single bite from a mosquito carrying infective larvae [1]. Mosquitoes get indoors easily. The risk is lower for a dog that rarely goes outside, but it is not zero. ### Can I get worms from my dog? Some intestinal worms, including roundworm and hookworm, can infect people, and children are often most at risk because of play habits and hand-to-mouth contact. Heartworm is not spread from dogs to people by contact. Good handwashing, prompt stool pickup, and regular deworming lower the household risk. ### Why does my dog need a heartworm test before starting prevention? Prevention kills larvae, not adult worms, so giving a preventive to an already infected dog does not clear the infection. Testing first tells your veterinarian whether adult worms are present and helps set the right plan. Testing also catches infections that slipped through missed doses. ### Are heartworm and intestinal worms treated the same way? No. Heartworm treatment uses melarsomine injections or, in some cases, long-term macrocyclic lactones with doxycycline [4]. Intestinal worms are treated with dewormers aimed at the gut. Your veterinarian will match the treatment to the parasite and to your dog's weight and health. ## Related Articles - [How To Know If Dogs Got Worms](/knowledge/veterinary-medicine/parasitic-diseases/how-to-know-if-dogs-got-worms) - [How Do I Know If My Dog's Got Worms](/knowledge/veterinary-medicine/parasitic-diseases/how-do-i-know-if-my-dog-s-got-worms) - [Can A Human Get Dog Worms](/knowledge/veterinary-medicine/parasitic-diseases/can-a-human-get-dog-worms) - [How To Tell If Dog Has Worms Or Parasites](/knowledge/veterinary-medicine/parasitic-diseases/how-to-tell-if-dog-has-worms-or-parasites) - [How To Tell If Dog Has Worms](/knowledge/veterinary-medicine/parasitic-diseases/how-to-tell-if-dog-has-worms) - [How Do I Know If My Dog Has Worm](/knowledge/veterinary-medicine/parasitic-diseases/how-do-i-know-if-my-dog-has-worm) ## References 1. [Heartworm Disease in Dogs - Dog Owners](https://www.merckvetmanual.com/dog-owners/heart-and-blood-vessel-disorders-of-dogs/heartworm-disease-in-dogs). Merck Veterinary Manual. 2. [Treatment of heartworm (Dirofilaria immitis) disease in dogs in the USA: general findings and cost of disease](https://pubmed.ncbi.nlm.nih.gov/42625190/). Parasites & vectors, 2026. 3. [Heartworm disease](https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/heartworm-disease). Cornell University College of Veterinary Medicine. 4. [Heartworm Disease in Dogs, Cats, and Ferrets - Circulatory System](https://www.merckvetmanual.com/circulatory-system/heartworm-disease/heartworm-disease-in-dogs-cats-and-ferrets). Merck Veterinary Manual. 5. [Serological and molecular detection of Dirofilaria immitis in pet dogs of Lahore, Pakistan](https://pubmed.ncbi.nlm.nih.gov/41881496/). Annals of parasitology, 2026. 6. [Evaluation of the trūRapid™ FOUR heartworm antigen test: a reliable point-of-care diagnostic tool for heartworm detection in dogs](https://pubmed.ncbi.nlm.nih.gov/42693482/). Parasites & vectors, 2026. 7. [Milbemycin oxime and lotilaner for heartworm prevention in dogs in Korea: a randomized controlled field trial](https://pubmed.ncbi.nlm.nih.gov/42676020/). Journal of veterinary science, 2026. ## Further Reading - [Merck Veterinary Manual: Dog Owners](https://www.merckvetmanual.com/dog-owners) - [Cornell Richard P. Riney Canine Health Center: Canine Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information) - [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)