Canine Worm Identification

Worm infections are common in dogs.
Collie Dog on Dog Bed image by Janet Wall from

Worms are one of the disgusting realities that pet owners have to deal with. There are many types of worms your dog can get. You can see some types of worms in your dog's vomit or feces; other types of worms are too small and are only viewable under a microscope. Learn how to identify worms and recognize symptoms of parasite infections in your dogs. Over-the-counter treatments are available for most types of worms, but because worm identification can be tricky, always seek veterinary advice before beginning a treatment program.


Roundworms are the most common type of worms found in dogs. Dogs get them by eating animals infected with the parasites or by eating soil or feces that is contaminated with roundworm eggs. Pregnant dogs can pass roundworms to their puppies in the womb or during nursing. Adult roundworms are several inches long and white or light brown in color. Pet owners may notice the presence of the adult worms in their dog’s vomit or feces. Dogs with major cases of roundworms may experience weight loss and have a potbellied appearance and a dull coat. Take your dog to a veterinarian to get medication as soon as you suspect a roundworm infection to prevent complications. Adult roundworms live in the small intestines. Large numbers of the worms can cause an intestinal blockage. Larvae, which are immature worms, may travel to the lungs and cause a lungworm infection, also called verminous pneumonia. Coughing can be a sign of a lungworm infection.


Hookworms are microscopic worms that use their hook-shaped teeth to attach to the intestinal lining, allowing them to feed off the blood of their hosts. Severe hookworm infections can lead to enough blood loss to cause anemia. Dogs can contract hookworms by eating infected animals or by ingesting larvae found in the environment, or through skin contact. Hookworm larvae can penetrate the skin. Pregnant and nursing dogs can transfer hookworms to their puppies. Because hookworms are microscopic, you cannot see them in your dog's feces without a microscope. Some dogs exhibit symptoms of an infection, which may include weight loss, diarrhea, and tarry or bloody stools. Have your dog screened for hookworms regularly by your veterinarian. An untreated hookworm infection can lead to severe anemia, resulting in sudden death in young, elderly and weak dogs.


Whipworms are microscopic worms that live in the large intestine and cecum, the area where the small and large intestines meet. The whip-shaped worms bury their long necks into the intestinal lining and feed off the host's blood. Dogs contract whipworms through ingesting the eggs found in contaminated soil or feces. You cannot see whipworms in your dog's feces because they are too small. Infected dogs may exhibit signs of weight loss, diarrhea, bloody stool and be in poor overall health. In rare cases, massive rectal bleeding can occur. Severe infections can cause electrolyte imbalances. Untreated whipworm infections can cause death. Not all infected dogs show symptoms. Annual fecal screenings at a veterinarian's office are useful for detecting whipworm infections in dogs.


Tapeworms are long, flat tape-like worms that live in the small intestine. The worms attach to the intestinal lining and absorb food through their skin. A tapeworm body is made up of segments. Each segment contains reproductive organs. You can identify tapeworm segments in your dog's feces or on your dog's anus. The segments are short, flat and whitish in color, and about 1/4 to 1/2 inch long when alive. Dead segments are a golden yellow and look like a flat grain of rice. Occasionally, segments exit the dog's anus attached and will look like a long, flat ribbon. Dogs most commonly contract tapeworms by ingesting fleas infected with the larvae, but they can also contract the worms by ingesting infected animals. Tapeworms usually do not cause problems for dogs, but stomach upset or diarrhea can occur. Your veterinarian can prescribe tapeworm medication to rid your dog's infection. Talk to your vet about flea control to prevent future infections.


Heartworms are the most dangerous worms to dogs. They are transmitted to dogs through a bite from an infected mosquito. The worms take residence in the heart and sometimes in other organs, including the lungs, kidneys and liver. A severe infection can prevent the heart from working properly. Small dogs can exhibit symptoms with only a few worms in the heart. Infected dogs may tire easily and experience shortness of breath or coughing. Even with treatment, heartworms can be fatal. Talk to your vet about preventive heartworm medicine. Dogs must be tested for a heartworm infection before preventive medicines are taken.

Stomach Worms

There are several species of stomach worms that dogs can get. The worms live and feed in the stomach. Dogs contract stomach worms from eating insects or animals that are infected with the parasites. Dogs commonly only have a few worms or even only one worm in their stomach and may be symptom free. Symptoms can include appetite loss, weight loss, vomiting and dark feces. You may notice a worm or multiple worms in your dog's vomit. Stomach worms are slender and small, reaching 30 to 40 mm in length. Untreated, severe cases of stomach worms can lead to anemia. Take your dog to a veterinarian if you suspect stomach worms.


Coccidia are microscopic, single-celled organisms that live in the intestines. Dogs contract coccidia through ingesting contaminated dirt or feces or by eating infected animals. Young puppies and weak animals are especially susceptible to coccidia infections. Symptoms of coccidia include bloody and watery diarrhea. Coccidia are too small to see. If you suspect a coccidia infection, take your dog to a veterinarian for treatment. Severe infections can cause death in young or weak animals. Treatment consists of supportive medications to help your dog's immune system fight off the coccidia infection.


Giardia is a microscopic single-celled organism that inhabits the small intestine. Dogs get giardia from ingesting water or food that has been contaminated with infected feces. Dogs of any age can get giardia, but it is most common in young puppies. You cannot see giardia in your dog's feces. An infected dog may exhibit signs of chronic diarrhea, watery stools, appetite loss, weight loss, dehydration or lethargy. Your veterinarian can examine your dog's feces under a microscope to detect giardia, and he will prescribe treatment if an infection is present. Reinfection is common. Keep your dog's area clean of feces during treatment, and bathe your dog frequently to help prevent reinfection.

Worms and Humans

Most species of worms are species-specific, meaning worms that infect dogs usually do not infect humans. Humans can contract some of the types of worms that infect dogs through contact with the dog's feces or through the same modes that dogs catch the parasites. Do not panic, however; it is not common for pet owners to get worms from their dogs. To reduce the chance of human infection, get your dog treated for worm infections as soon as possible and wear gloves when cleaning an infected dog's feces. Talk to your doctor if you are concerned or suspect that you have worms.



About the Author

Rose Kivi has been a writer for more than 10 years. She has a background in the nursing field, wildlife rehabilitation and habitat conservation. Kivi has authored educational textbooks, patient health care pamphlets, animal husbandry guides, outdoor survival manuals and was a contributing writer for two books in the Uncle John’s Bathroom Reader Series.

Photo Credits

  • Collie Dog on Dog Bed image by Janet Wall from