Intestinal Parasites


Roundworms (ascarids) are the most common intestinal parasite of dogs and cats. Pets become infected by swallowing roundworm eggs or larvae (immature worms) found in contaminated soil or feces (stool), or by eating commonly infected rodents, birds and certain insects. Puppies and kittens are commonly infected by the mother while still in the uterus or from her milk. Swallowed larvae travel through the body to the intestine, where they develop into mature worms. There, adult females deposit eggs, which pass with the feces and develop into infective larvae.

A diagnosis is made by identifying the eggs during microscopic examination of a fecal sample.

Human infection with roundworm larvae is possible but does not occur frequently if good hygiene is practiced, since eating contaminated feces or soil is necessary for infection. Children should be taught the importance of cleanliness when playing with animals, especially litters of puppies and kittens. The best insurance against human infection is keeping your pet free from roundworms by regular fecal examination and treatment if necessary. Prophylactic worming of all kittens and puppies is recommended due to this public health concern.

GOOD SANITATION IS ESSENTIAL: All feces should be removed promptly from area where your pet is confined. Eggs can remain viable in soil for years, so contaminated ground becomes a source of re-infection. This is especially true of dog pens, runs or areas where your pet may be tied. Control measures for these areas include:

  • Turning the soil over to a depth of 8-12 inches after your pet is free of worms.
  • Replacing dirt runs with concrete (this seems to be the most effective control procedure).
  • Removing feces daily.
  • Moving your pet to a new uncontaminated area.

It is recommended to examine a fecal sample annually when your pet is in for its physical examination to prevent re-infection.

Tapeworm Infection:

The tapeworm is a parasite found in the intestines of dogs and cats. It consists of a head and a long flat body made up of segments. Segments are passed in the animal’s feces (stool) at variable times, leaving the head still attached to the animal’s intestinal lining to produce new segments.

Tapeworm infection may not cause noticeable illness in your pet, or it may produce digestive upsets, poor appetite, poor hair coat and skin, weight loss and vague signs of abdominal discomfort.

Tapeworm infection is usually diagnosed by finding the segments in your pet’s feces, in its bed, or clinging to the hair around the anus. Microscopic examination of feces is not always a reliable method of diagnosing tapeworms, as the eggs MAY NOT be present in the feces. When first passed, segments are yellowish to white, about 1/4 inch long, and may expand and contract. When dry, the segments resemble sesame seeds or grains of rice.

Tapeworms are not passed directly from pet to pet, but require an intermediate host in which to develop. Common intermediate hosts are fleas, and small animals such as mice, squirrels and rabbits.

Treatment will destroy the tapeworms already infecting your pet. Re-infection is controlled by eliminating or reducing contact with intermediate hosts. Since the flea carried tapeworm is by far the most common tapeworm we encounter, flea control needs to be done on your pet(s) and in your home and yard to try and prevent re-infection.


Giardia is a single-cell organism (protozoa) that can infect the intestinal tract of people and most types of domesticated animals. Infection can occur when contaminated feces, food, or water is ingested.

The most common clinical sign of Giardia is diarrhea. Other signs may include weight loss, vomiting, and lethargy. A diagnosis is made by identifying the organism during a microscopic examination of the feces (stool). Diagnosis may be difficult and sometimes multiple fecal samples may need to be examined using specialized staining techniques.

Several drugs have been used to treat Giardia infections in dogs and cats because the organism can be difficult to eliminate. Once your pet has finished the course of medication, WEAR GLOVES and wash around the anus and base of tail. This will help prevent re-infection of your pet by removing any infected organisms they may lick from their anus.

To prevent re-infection by Giardia it is important to do environmental control. All feces should be removed and properly disposed of, and contaminated cages, crates, yards, and runs should be cleaned thoroughly. Since Giardia is a relatively common intestinal parasite of people, good personal hygiene should be practiced in homes where Giardia has been diagnosed in your pet. Children should not handle the pet’s feces and good environmental sanitation is imperative.


Coccidia is a parasitic disease of the intestinal tract caused by a small organism (protozoa) visible only with the aid of a microscope. The disease generally spreads from one animal to another by contact with feces (stool) from infected animals. The most common clinical sign is diarrhea and younger or weakened animals are most adversely affected. Malnutrition also has a role in enhancing the severity of the disease. A diagnosis of coccidia is made by identifying the parasite during microscopic examination of the feces.

Therapy for coccidia consists of administering antibiotics and correcting other underlying problems, e.g. malnutrition or a contaminated environment. A high quality balanced diet should be provided, and infected animal(s) should be separated from non-infected ones. All bedding, food and water dishes, etc. should be kept clean and feces should be removed daily.

Once treatment is finished, it is recommended to recheck a fecal sample to ensure that the parasite has been eliminated.


Whipworms (trichurus vulpis) are intestinal parasites of dogs. Infected dogs pass whipworm eggs in their feces (stool). Other dogs become infected when they ingest these eggs. After they are swallowed, the eggs pass to the intestine where they hatch into larvae that develop into adults. The adults then lay eggs, which are passed in the animal’s feces. Several months may elapse before this cycle is completed.

Whipworms attach to the wall of the gut and suck blood for nourishment. This causes inflammation and irritation of the gut and results in diarrhea. If the infection is mild, there may be no obvious signs. In more serious cases, signs may include weight loss, diarrhea with blood or mucus, and possibly anemia (a harmful decrease in the total number of red blood cells or in the hemoglobin, the oxygen carrying protein the red blood cells contain).

A microscopic examination of a fresh fecal sample is performed to detect whipworm eggs. Therapy consists of administration of an appropriate deworming medication that kills the worms.

Whipworm eggs are very durable and resist prolonged freezing. They can remain viable in the environment for years. They are virtually impossible to remove with chemicals. The key to control is effective disposal of feces. Feces should be removed from the yard or run and disposed of elsewhere. This is especially important after deworming medications have been given. Fecal samples should be examined one month after the animal has been dewormed and then at three and six months to make sure infection has not recurred.


The hookworm (Ancylostoma caninum, Ancylostoma braziliense) is one of the classical internal parasites of puppies, the others being roundworms, tapeworms, and coccidia. (There are species of hookworms that infect cats but hookworm infection in cats is not nearly as common as hookworm infection in dogs.) Hookworm infection has several special features that are of interest to us as the caretakers of dogs:

  • Hookworms suck blood.
  • Hookworms can be transmitted to unborn pups.
  • Hookworms can infect humans.

The adult hookworm lives in the small intestine of its host. It hangs on to the intestinal wall using its six sharp teeth and unlike other worms that just absorb the digested food through their skin as it passes by; the hookworm drinks its host’s blood. Hookworm eggs are released into the intestinal contents and passed into the world mixed in with the host’s stool. The larva can infect its new host in several ways. One way is to penetrate the host’s skin directly through the feet or belly or whatever part of the skin is touching the ground. Another way for the larva to gain entry to the new host is to be present in soil that is licked and swallowed by the host as it cleans itself.

Once the larvae are inside the host, they make their way to the intestine where some worms simply stay and mature into adulthood. Other individuals are bolder, tunnel out of the intestine, and migrate to the lung tissue. Not all the worms that begin this treacherous migration complete it. These larvae remain inactive but periodically some will emerge and complete their migration.

The adult worms live by sucking blood from the intestine. The host passes the eggs into the environment where a new host picks them up. The developing larvae may migrate widely through the new host’s body before settling down to complete their maturation.

A microscopic examination of a fresh fecal (stool) sample is performed to detect hookworm eggs. Therapy consists of administration of an appropriate deworming medication that kills the worms.

Contaminated soil is an important hookworm source when it comes to a human disease called Cutaneous Larva Migrans. Running barefoot through the park or beach may seem pleasant but if the soil has been contaminated with canine fecal matter, the eager infective larvae may be waiting to penetrate your skin. Hookworm infection in the skin is intensely itchy but usually treatable. The local restrictions on bringing dogs to local beaches and the strict clean-up laws reflect concern for hookworm (and roundworm) infection in people. Humans can also become infected by eating improperly washed vegetables, which may harbor contaminated soil.


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