Whipworms and Parasites in Dogs

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Whipworms and Parasites in Dogs

The adult whipworm is 2 to 3 inches (50 to 76 mm) long. It is threadlike for the most part, but is thicker at one end, which gives it the appearance of a whip.

The adult worm lives in the last part of the small intestines and the first part of the large intestines, where it fastens to the wall of the gut. The female lays fewer eggs than other worms, and there are long periods during which eggs are not shed. Accordingly, finding eggs in the feces is difficult, even with repeated stool examinations.

Whipworms can cause acute, chronic, or intermittent diarrhea in dogs. Typically, the stool is mucoid and bloody. The diarrhea is often accompanied by urgency and straining (see Colitis). Dogs with a heavy infestation may lose weight, fail to thrive, and develop anemia.

Treatment: A number of preparations are effective against whipworms. They include Panacur, Drontal Plus, Telmintic, and Vercom Paste. However, it is difficult to attain high drug concentrations in the colon, where the whipworms reside, and this makes them difficult to eradicate. To maximize success, follow up the initial deworming with a second deworming three weeks later and a third deworming in three months.

Prevention: Eggs remain infective in the environment for up to five years. In areas such as public parks and backyards, where the ground has been heavily contaminated with whipworm eggs, frequent reinfection is a common problem. It is important to observe pooper-scooper ordinances and remove stools in the yard every day. Dirt runs should be relocated and paved with concrete or new gravel. Use household bleach in a 1:32 dilution to disinfect concrete and gravel runs. It may be necessary to totally change the gravel in gravel runs.

The drug Interceptor, given to prevent heartworms, also controls and prevents whipworms.

Threadworms (Strongyloides)

Threadworms are round worms just 2 mm long that live in the small intestines and infect both dogs and humans. The parasite is found in humid, subtropical regions such as the southeastern United States and Gulf Coast areas.

The life cycle of the threadworm is complex. Eggs and larvae are passed in the feces. Larvae become infective and are either ingested or gain entrance by directly penetrating the skin.

Threadworms are mainly a problem in puppies. Infected pups suffer from a profuse watery or bloody diarrhea that can be fatal. Pneumonia may occur as the larvae migrate through the lungs.

Treatment: The diagnosis is made by finding eggs or larvae on microscopic examination of stool, both fresh and after incubation. A five-day course of Panacur is the treatment of choice. Retreatment in 30 days is recommended. Ivermectin has also been used effectively, although it is not labeled for this purpose.

Public health considerations: Dogs can readily infect humans, and vice versa. Threadworm infection in humans is a debilitating disease accompanied by chronic diarrhea. Accordingly, infected pups must be isolated until treated and cured. Extreme care must be taken to avoid human contact with the feces of dogs infected with threadworms.

Other Worm Parasites


Pinworms are sometimes a concern to families with pets and children. However, dogs and cats are not a source of human pinworm infection, because they do not acquire or spread these parasites.


This is a disease acquired by ingesting uncooked pork containing the encysted larvae of Trichina spiralis. In humans, only a few cases are reported each year. The incidence is probably somewhat higher in dogs. Prevent trichinosis by keeping your dog from roaming, especially if you live in a rural area. Cook all fresh meat for you and your dog.


Lungworms are slender, hairlike parasites about 1 centimeter long. There are several species of lungworm that affect dogs. Capillaria aerophila is acquired by ingesting eggs or a transport host, such as snails, slugs, or rodents. These parasites reside in the nasal cavity and upper air passages, producing a mild cough. Filaroides species produce a tracheal and bronchial infection that tends to be a kennel-related problem, especially in Greyhounds.

Most dogs with lungworms have mild infections and do not show clinical signs. Heavily infested dogs (usually under 2 years of age) may have a persistent dry cough, weight loss, and exercise intolerance.

Diagnosis is based on clinical signs, a chest X-ray (not always positive), and identification of the eggs or larvae in the stool or in respiratory secretions. Bronchoscopy on a dog with a Filaroides infection may reveal small nodules in the wall of the trachea. Larvae may be seen peeking out of these growths. Treatment with Panacur (fenbendazole) is often needed for extended periods of time.

This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.

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Reviewed on 12/3/2009 11:30:02 AM

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