Common Worms and Intestinal Parasites in Dogs

Roundworms

Roundworms (Toxocara Canis, Toxascaris leonine) are the most common intestinal parasites in dogs. They are especially common in puppies.

Adult roundworms live in the intestinal tracts of their hosts, consuming that host's food. The adult roundworm is round, white to light brown in color, and several inches long. These worms look a lot like spaghetti or angel hair pasta.

Adult dogs get roundworms from ingesting roundworm larvae, usually from contaminated soil or infected prey (such as a mouse or other small mammal).

Puppies are born with roundworms after contracting them from their mother's uterus during gestation. In addition, nursing puppies may ingest roundworm larvae in their mothers' milk.

Once ingested, larvae make their way to the dog's liver. While developing into adult worms, they travel to the lungs, are coughed up by the dog and then swallowed. The adult roundworms live in the dog's intestines. Their eggs are shed in the dog's stool and develop into larvae. The life-cycle is repeated when another host ingests the larvae.

Signs

Signs of roundworm infection include diarrhea, vomiting, pot-bellied appearance, coughing (dogs may cough up or vomit worms), weight loss, and dull hair coat. Many dogs will show no signs of infection at first.

Diagnosis

Your veterinarian can test a sample of stool from your dog for worms by running a lab test called fecal flotation. Roundworm eggs are microscopically visible in the stool if adult roundworms are present in the small intestine.

Treatment

Treatment of roundworms involves multiple oral doses of deworming medication. Deworming only kills the worms in the intestinal tract, so repeated doses are necessary to kill newly developing adult worms. Because puppies are so commonly affected, they are routinely dewormed (whether or not eggs are seen microscopically) during their first few sets of puppy vaccines. Be aware that not all over-the-counter dewormers are effective. Your veterinarian is the best source for this medication. Note: Several types of heartworm prevention also protect against roundworms.

Zoonosis

Humans can contract roundworms through contact with contaminated soil, potentially leading to a serious condition called Visceral Larva Migrans. Always wear gloves when handling any soil, especially that which may have come in contact with dog feces. Children are at especially high risk.

Hookworms

Hookworms (Ancylostoma caninum, Ancylostoma braziliense) are another common intestinal parasites affecting dogs and puppies. The hookworm attaches itself to the intestinal mucosa of its host with its sharp teeth and sucks the host's blood for sustenance. Hookworms are significantly smaller than roundworms and not usually seen in stool or vomit.

Adult dogs get hookworms from contact with contaminated soil that contains hookworm larvae. The larvae burrow through the skin or paw pads when a dog is lying on the ground. Or, the dog can ingest the larvae after contact with contaminated soil, often when grooming. As with roundworms, nursing puppies may ingest hookworm larvae in their mothers' milk.

Many hookworm larvae develop into adult worms in the small intestine, but some travel to the lungs, are coughed up by the dog and then swallowed (similar to roundworms). The adult hookworms live and mate in the dog's small intestine. Their eggs are released into the environment via the dog's stool. The hookworm eggs hatch into larvae and live in the soil. The life-cycle is repeated.

Signs

Signs of hookworm infection include pale mucous membranes and weakness (due to anemia). Some animals have diarrhea and/or weight loss. Many dogs show no signs of infection at first. Be aware that hookworm infection can be very dangerous to young puppies because of the amount of blood loss that can occur.

Diagnosis

Diagnosis is made after collecting a stool sample and running a lab test called a fecal flotation (as with roundworms). The hookworm eggs will typically be seen microscopically if adult hookworms are present in the small intestine.

Treatment

Treatment of hookworms is similar to that of roundworms. Multiple oral doses of a deworming medication must be given since the dewormer can only kill worms in the intestinal tract. The dewormer that is typically given during puppy vaccines also treats for hookworms. Not all over-the-counter dewormers are effective, so ask your veterinarian about the right medication. Note: several types of heartworm prevention also protect against hookworms.

Zoonosis

Humans can get hookworms through contact with contaminated soil. Hookworm larvae can penetrate the skin, potentially leading to a relatively minor but rather uncomfortable condition called Cutaneous Larva Migrans. Avoid walking barefoot in areas where pets may have once defecated (including beaches). Again, always wear gloves when handling any soil, especially if it came in contact with dog feces. Children should never play or sit in areas where pets may have once defecated.

Whipworms

Whipworms (Trichuris vulpis) are another common intestinal parasite in dogs. The whipworm lives in the large intestine, where it bites the tissue and embeds its head inside. Like the hookworm, the whipworm sucks the host's blood for sustenance. Whipworms are even smaller than roundworms and rarely seen in the stool. One end of the worm's body is wide while the rest tapers off to a narrow, whip-like head, hence the name "whipworm".

Dogs get whipworms from ingesting whipworm eggs that live in the soil. This typically happens through self-grooming. The whipworm eggs pass through the upper GI tract and hatch into larvae in the small intestine. Next, the larvae move down to the cecum or large intestine where they develop into adult whipworms. Their eggs show up in the dog's stool. Whipworm eggs can lay dormant in the soil for years until consumed by a new host. Then, the life-cycle is repeated.

Signs

Signs of whipworm infection may not be present at first. Typically, bloody diarrhea will develop as the infection worsens, possibly leading to chronic bloody diarrhea. Anemia is possible, though not as common with whipworm infection as it is with hookworm infection. A whipworm infection can also become severe enough to cause a serious electrolyte imbalance.

Diagnosis

Diagnosis of a whipworm infection can be difficult because whipworms do not continuously lay eggs the way roundworms and hookworms do. Your veterinarian will run a lab test called a fecal flotation (as with roundworms and hookworms). The whipworm eggs may or may not be seen microscopically if adult whipworms are present in the small intestine. A lack of eggs in the stool sample will not definitively rule out whipworm infection. Your veterinarian may recommend repeated fecal testing if whipworms are suspected.

Treatment

Treatment of whipworms is similar to that of roundworms and hookworms. Multiple doses of a special deworming medication must be given. Over-the-counter dewormers are not effective, so your veterinarian must provide you with the right medication. Because of the long life cycle of the whipworm, treatment is typically repeated months later. Note: Certain types of heartworm prevention also protect against whipworms.

Zoonosis

Fortunately, the type of whipworm that affects dogs is rarely transmissible to humans. However, precautions should still be taken to prevent contact with dog feces or contaminated soil.

Tapeworms

Tapeworms (Dipylidium caninum) are intestinal parasites that commonly affect dogs. They are long, flat (tape-like) worms that attach to the small intestine of their host. A tapeworm body is several inches long but consists of multiple segments that grow onto the head and neck of the worm. Each segment has its own reproductive tract.

Dogs get tapeworms from ingesting fleas. Flea larva hatch from eggs and consume surrounding flea dirt and debris. If present, they will also consume tapeworm eggs. The larval fleas develop into adults as the tapeworm eggs develop inside the fleas. Adult fleas jump on a host (usually a dog or cat) and cause the pet to itch. The host chews itself and consumes the adult flea, then the developing tapeworm is released into the host. The young tapeworm attaches to the small intestine and grows into segments.

The end segments are egg sacs which eventually detach and make their way out of the host's rectum into the environment. The tapeworm segment, which resembles a grain of rice or a sesame seed, breaks open and the eggs are released. If flea eggs are also present in the environment, the life cycle is repeated. Therefore, tapeworms are only passed from pet to pet by way of fleas.

Signs

Signs are rarely seen in dogs affected by tapeworms (except the appearance of rice-like segments around the anus of the pet and/or in the stool. Fortunately, these parasites do not tend to adversely affect dogs. They're generally considered a cosmetic and hygienic concern only.

Diagnosis

Diagnosis of tapeworms is typically made after the flat, rice-like segments are seen by the owner or a pet professional. Tapeworm eggs rarely appear microscopically when fecal flotations are run.

Treatment

Treatment of tapeworms involves one or more doses of a special deworming medication. Typical over-the-counter dewormers are not effective. Your veterinarian must provide you with the right medication. Because tapeworms are transmitted via fleas, the only way to prevent re-infection is to eradicate fleas. Deworming may need to be repeated while you try to control fleas. The use of monthly flea prevention is recommended.

Zoonosis

Fortunately, the type of tapeworm that affects dogs is not directly transmissible to humans. However, tapeworm infection can technically be transmitted to humans by accidental ingestion of a flea.

Note: There is another type of tapeworm that can affect pets: Taenia. This type of infection is less common and contracted after a pet consumes an intermediate host such as a rabbit or mouse. Fortunately, this type of tapeworm does not tend to have an adverse effect on the host. In addition, the same medication that kills Dipylidium caninum also kills Taenia.