What Causes Worms In Dogs?

Dogs exposed to contaminated soil or feces, grooming or licking by an infected animal, or contact with mosquitos can result in worms in dogs. Depending on the type of parasite, infections could affect the heart and arteries, lungs, intestines, or skin, and side effects might include diarrhea, vomiting, and lethargy.

How do dogs get worms?

Worms in dogs are a relatively common condition. They are often referred to as intestinal parasites, which can infect adult dogs and nursing puppies. Some worms can be transferred to people, young children or immunosuppressed people are the most susceptible.

While up to 90% of puppies are born with roundworms or hookworms passed down from their mother, veterinarians often manage cases in which an adult dog has contracted or transferred microscopic whipworm, tapeworm, and heartworm larvae through contaminated environments, mosquito bites, and licking.

Here are some of the common scenarios in which a dog may contact worms:

  1. Roundworm eggs flourish and spread in dog feces, infecting grass, sand, and soil.
  2. Female dogs transfer roundworms to puppies through their milk.
  3. Tapeworms develop after dogs ingest fleas or consume diseased rodents.
  4. Hookworms are acquired through dogs licking their skin and coat.
  5. Puppies get hookworms transferred by their mothers.
  6. Mosquitos carry heartworm larvae and infect animals through bites.
  7. Grooming tools and contaminated soil can carry whipworm eggs.
  8. Ringworm spores, which is not a worm but a fungus, can be transferred from soil or other infected animals and can result in the development of hairless, dry, and round patches of skin.

Heartworm Life Cycle

  1. A mosquito bites an infected dog and ingests tiny heartworm larvae along with the animal’s blood. Other carriers of heartworm disease include wolves, foxes, ferrets, coyotes, and raccoons.
  2. Inside the mosquito, these larvae develop into their infective stage.
  3. When the same mosquito bites another dog, the larvae infect the healthy animal.
  4. Without a monthly dose of preventive, the larvae continue to develop inside the dog, eventually reaching the heart and lungs.
  5. One million dogs are estimated to be heartworm positive in the United States each year.

Which symptoms of worms in dogs are common?

Symptoms of worms in dogs are dependent on the type of worm, some signs of infection are more obvious than others.

For example, a dog with heartworm infection, transferred through a bite of an infected mosquito can have respiratory difficulty, coughing, weight loss, or can exhibit exercise intolerance. The result is that a dog may look like he does not want to go for a walk or to play.

More common worms in dogs, like hookworm, tapeworm, or roundworm share similar symptoms, making it more challenging to diagnose based on symptoms alone. Your veterinarian may recommend a fecal screening to determine the type of parasitic infection and the most appropriate treatment.

Many infected dogs do not show signs of worms at all, however, regular veterinarian check-ups that include a fecal test annually can help prevent or minimize intestinal parasite infections.

Giving your dog a monthly heartworm preventative will also help to prevent infections by some of these more common intestinal parasites.

Should a dog experience any of the symptoms below, it’s highly recommended that you visit a veterinarian as soon as possible for an accurate analysis, treatment, and advice on how to protect your dog from further parasitic infections.

Symptoms of infections when there are worms in dogs
Roundworms Tapeworms Hookworms & Whipworms
vomiting lethargy coughing
diarrhea abdominal bloating bloody diarrhea/stool
coughing appetite increase or decrease lethargy
lethargy weight loss abdominal bloating
abdominal bloating itchy skin weight loss
appetite increase or decrease rubbing rear-end along the floor itchy skin
itchy skin spaghetti-like worms in feces rubbing rear-end along the floor
rubbing rear-end along the floor rice-like segments in fur or feces  
spaghetti-like worms in feces    

Can puppies get worms?

Up to 90% of puppies, three months and younger are diagnosed with intestinal parasites. Parasitic infection in your puppy should be treated immediately by a veterinarian.

Puppies have delicate immune systems that are unable to efficiently fight off certain infections and veterinary treatment must be a priority if any of these symptoms occur. 

What are the types of worms in dogs?

While there are only five types of worms in dogs that are most prevalent, each type contains multiple species within it. Learn about the types of worms in dogs, their species, and how veterinarians identify them.


  • Species: Toxocara canis, Toxascaris leonine
  • Description: Spaghetti-like, long white strings with three nodules at the top of a round head that opens into a mouth. Roundworms lay approximately 85,000 eggs per day.
  • Infects: Intestine, eating ingested food, and depriving dogs of nutrients, sometimes causing an obstruction within the organ and further signs of illness.


  • Species: Ancylostoma braziliense, Ancylostoma caninum, Uncinaria stenocephala
  • Description: Spaghetti-like, long worm with a defined hook-like head at one end and very sharp teeth.
  • Infects: Hooks sharp teeth into the intestine, resulting in bleeding that the worms feed off of.


  • Species: Trichuris vulpis, multiple Trichuris spp
  • Description: White worm with a whip-shaped long neck and short, whip-shaped handle body.
  • Infects: Burrows its long, thin neck into the intestinal wall to feed.
  • Danger: Whipworm eggs remain active in the environment or on the ground for up to five years.


  • Species: Taenia, Echinococcus, Dipylidium caninum
  • Description: Flat, long, segmented ribbon-like worm, that grows to approximately 8 inches. Easily identifiable as small grains of rice-like segments at the base of a pet’s tail or in the fur around the anus.
  • Infects: Intestinal lining, attaching to the wall with a hook-like mouth.
  • Danger: Tapeworms are passed onto dogs through fleas, which are ingested as they bite at itchy spots.


  • Species: Dirofilaria immitis
  • Description: Long, noodle-looking, transparent worms.
  • Infects: Heart blood vessels.
  • Danger: Can cause heart problems. Dogs in North American should be treated with heartworm medicine once a month. 

How to prevent worms in dogs

Protecting a dog from intestinal parasites begins with advice that most veterinarians would offer pet parents: Always pick up after your dog and discard the feces safely to prevent spreading diseases, reinfection, or infecting any other animals.

  • Deworm dogs and puppies regularly.
  • Request a fecal analysis from your veterinarian.
  • Keep areas where dogs eat, sleep and relax cleaned.
  • Wildlife is best appreciated from afar! Make sure your dog is not coming into contact with any wild animals or their feces.
  • Heartworm medicine is essential for every dog to stay healthy and should be administered monthly.
  • Always wash your hands after handling dog feces or touches trash bin lids.
  • Wear gloves while gardening to avoid picking up parasites left in the soil by animals.
  • Avoid walking barefoot on lawns and grass or wash feet immediately after.
  • Avoid environments that can possibly be contaminated by pet feces — plants, soil, or sand — and keep your pets away from these areas.
  • It is important to keep your pets on a monthly heartworm preventive that also treats and controls intestinal parasites.
  • The CDC recommends pet owners promptly remove pet feces from the environment.

Misconceptions About Intestinal Parasites


Intestinal parasites such as hookworms and roundworms can only infect dogs, not people.



Hookworms and roundworms can pose a serious threat to humans, especially children.

Almost 73% of pediatricians in the US reported cases of children with parasitic infections.



Ingestion of larvae is the only transmission method for hookworm infection in people.



In addition to ingestion, hookworms can also infect by penetrating the skin. That is a unique ability hookworms have. So pets, as well as people, can get infected if their skin comes in direct contact with the contaminated areas.