Intestinal Worms in Dogs

Eirevet is a veterinarian specialized in canine and feline internal medicine who owns a small animal veterinary hospital in Ireland.

Every dog born outside of a strictly controlled setting is born with worms. While the puppy is still within the womb, worms which may have laid dormant in the mother's body for years become active and migrate across the placenta to parasitise the unborn fetus. This staggering opportunism demonstrates just how highly evolved the relationship between host and parasite has become over millennia.

Due to their sophisticated transmission methods, dog worms have proven impossible to eliminate completely, and responsible dog ownership must involve regular deworming of pets to control the population of worms within the pet. By ensuring that your dog's number of worms does not get out of control, you can ensure that your dog never has to develop signs of disease associated with these parasites.

Roundworms in Dogs (Toxocara canis)

Toxocara species are the most common roundworms found in pet dogs worldwide. These large, white worms are the ones usually associated with the transplacental infestation mentioned above. As well as puppies acquiring these worms in the womb, they are also passed through the bitch's milk in the first few days of life.

After ingestion, the worm larvae migrate through the pup's intestinal wall via the liver to the lungs. They are then coughed up, swallowed, and develop to adults in the puppy's digestive tract. Disease may develop as a result of parasite migration or due to large numbers of adult worms in the intestine. Clinical signs relate to the site of the problem and may include:

  • pneumonia
  • liver damage
  • bowel obstruction
  • bowel perforation

Adult dogs that ingest worm larvae will usually develop an immune response to the parasite, resulting in the formation of cysts containing larvae in the liver, lungs, muscle and other tissues. The larvae may escape these cysts if the pet becomes stressed, immunosuppressed, or pregnant at a later date.

Toxocara is a zoonotic parasite, meaning that it can also infest humans. Children are particularly vulnerable. When canine roundworms infest species other than dogs, they may lose their normal ability to navigate between intestines and lungs, and their abnormal migration can result in the syndrome of visceral larval migrans. One of the more severe forms of this disorder occurs when the parasites inadvertently enter the eye, where they may cause a severe reaction in the retina, which is sometimes mistaken for a form of cancer (retinoblastoma).

Hookworms in Dogs (Ancylostoma caninum)

Hookworm infestations are most commonly caused by Ancylostoma caninum in warmer parts of the world, for example, in the mid- and southern United States. Uncinaria stenocephala (sometimes referred to as the fox hookworm) is more common north of these latitudes. As you can see from the magnified picture above, this family of dog worms is equipped with a fearsome set of teeth, which are responsible for the clinical signs seen in dogs and puppies with this infestation.

Young pups become infected by the larvae of these worms directly from their mother's colostrum (milk) within the first day of life. The larvae may also be ingested from the environment and can even burrow through the skin and travel through the unfortunate animal's bloodstream. The larvae again migrate to the lungs, where they are coughed up and swallowed before maturing in the gut.

The main problem caused by these worms in dogs is anemia due to blood loss. The adult worms bite through the mucosa lining the dog's gut in order to feed, and because of their sharp mouthparts they leave a bleeding surface behind when they move to a new feeding site. Digested blood may be seen in your dog's feces, but in some puppies, a sudden, severe, and sometimes fatal anemia is the first warning sign that the parasite may be present.

Whipworms in Dogs (Trichuris vulpis)

Of all the worms in dogs which we commonly see, whipworm infestations are usually the least severe. The adult worms of Trichuris vulpis reside in the rectum and large intestine of dogs. They can take up to three months to mature, and they can be very long-lived. The main problems they can cause relate to irritation and damage to the rectal wall, so straining to pass feces which may contain fresh blood is the most common combination of signs.

Tapeworms in Dogs (Echinococcus multilocularis)

The tapeworm family contains a great many species which may be found in pet dogs. Most of these parasites are acquired through feeding raw meat or hunting, with the notable exception being Dipylidium caninum. This worm is actually passed between pets by fleas. The infective stage of this parasite is called the scolex, which is a small white organism about the same size as a grain of rice, which may be seen crawling from your dog's rectum.

While tapeworms rarely cause serious disease in our pets, they can present a very serious health risk to humans. Members of the Taenia and Echinococcus families can infect humans, resulting in the formation of massive cysts and causing damage to internal organs, particularly the liver, lung, and brain.

Diagnosing Worm Infestations in Dogs

A heavy worm burden should be suspected in any puppy displaying signs of a potbelly, poor weight gain, poor coat quality, vomiting, diarrhea or anemia. Some pups may pass live worms in their feces, although again this is usually only seen in dogs with a large number of the parasites. In other pets it will be necessary for your veterinarian or a veterinary reference laboratory to perform investigations on a fecal sample from your dog.

Microscopic examination of a fresh fecal smear or a fecal flotation sample will reveal the presence of worm larvae or worm eggs depending on the types of worms present in your dog's gastrointestinal tract. For most of the common worms seen in dogs, these tests are very sensitive and are a useful part of routine health screening in any pet.

Prevention and Treatment of Worms in Dogs

While animals showing signs of disease relating to these parasites should be examined by a veterinarian and have fecal and other investigations performed, those without obvious signs can and should be treated regularly with effective anti-parasitic products.

The American Animal Hospital Association recommends that puppies should be treated as follows:

  • every two weeks from three weeks to nine weeks of age
  • every month from three to six months of age

The British Small Animal Veterinary Association recommends that adult dogs should be treated at least once every 3 months. I have displayed suitable products for these age groups below. These are safe and effective drugs which are routinely used by veterinarians for the treatment and prevention of intestinal and other worms in dogs.

Susan on May 23, 2015:

Might be blood- take your dogs to the vet!!

verlane mcdonald on February 09, 2015:

My dogs were eating perina wet and dry dig food in i noticed that there poop turned black so i switched t home made dog food two weeks latter there stools are still black but lumpy in breaks when i pick it up what could this be

Symptoms Of Worms In Dogs

Have you been wondering what the most common symptoms of worms in dogs are? Worms in dogs are one of the most common dog health problems and, although the thought of worms in your pup may be unpleasant, it’s important to identify the symptoms of worms in dogs so you can begin treatment right away.

There are five types of worms that generally affect dogs:

  • heartworms
  • roundworms
  • hookworms
  • tapeworms
  • whipworms

Disease Caused by Insects

Myiasis is the development of larval dipteran flies (bots and warbles) within the body’s tissues or organs. The larvae of Cuterebra, which are deposited under the skin in dogs or cats, have been known to wander into the central nervous system and affect the cerebrum or cerebellum. Organophosphate drugs can eliminate certain dipteran larvae from the nervous system, but they can also cause nervous system damage. Corticosteroid drugs are often recommended to prevent additional inflammatory damage and pressure on the brain during treatment (See also Flies and Mosquitoes of Dogs).

Intestinal Parasites Treatment

The parasites are typically treated with dewormers. Each type of parasite will require a different type of dewormer.

In addition to the medication, you may also opt for a few shampoos and lotions to help the dog's dry skin.

Immune system boosters may also be administered. If the dog is anemic, the vet may prescribe some supplements. In severe cases, IV fluids may be needed.

There are drugs that may be administered periodically to dogs to prevent the infection with intestinal worms.

How to Identify Different Dog Worms

Last Updated: October 10, 2020 References Approved

This article was co-authored by Pippa Elliott, MRCVS. Dr. Elliott, BVMS, MRCVS is a veterinarian with over 30 years of experience in veterinary surgery and companion animal practice. She graduated from the University of Glasgow in 1987 with a degree in veterinary medicine and surgery. She has worked at the same animal clinic in her hometown for over 20 years.

There are 10 references cited in this article, which can be found at the bottom of the page.

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There are many different types of worms that can infect dogs. Those of most concern are roundworms, tapeworms, heartworms, hook, and whipworms. Whilst each type of worm has a slightly different life cycle, the dog's symptoms can be consistent with different types of worm infections. Thus, it is not possible to determine what sort of worm your dog has based on symptoms alone, and tests may be necessary. [1] X Research source Prevalence of canine parasites based on fecal flotation. Iagburn, Lindsay, Vaughan et al. Comp Cont Ed Pract Vet 18, 483-509 However, knowing the general symptoms, risks, and characteristics of different types of worms can help you treat and care for your canine friend.

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