Whipworm Infections in Dogs

What are whipworms?

Whipworms are intestinal parasites that are about 1/4 inch (6 mm) long. They live in the cecum (a pouch that forms the first part of the large intestine) and large intestine of dogs, where they cause severe irritation to the intestinal lining. Whipworm infection results in bloody diarrhea, weight loss, and general debilitation. 

Of all the intestinal parasites found in dogs, whipworms cause the most disease.

How do dogs get whipworms?

Whipworms pass microscopic eggs in the stool. The eggs are resistant to drying and heat so they can remain alive in the environment for up to five years. Once laid, they mature to an infective stage and can re-infect a new dog in 10-60 days. The mature eggs are swallowed by the dog, hatch, and then mature into adults in the lower intestinal tract, completing their life cycle (see illustration).

"The eggs are resistant to drying and heat so they can remain alive in the environment for up to five years."

How are whipworms diagnosed?

Whipworms are diagnosed by finding eggs on microscopic examination of the stool. These eggs, however, are difficult to find. Whipworms pass small numbers of eggs on an inconsistent basis; therefore, some samples may be falsely negative. Multiple stool samples are often required to diagnose whipworms. Additionally, it takes approximately 11-12 weeks after hatching for a female adult to begin to lay eggs, so tests run soon after infection are often falsely negative.

Any dog with chronic diarrhea should be suspected to have whipworms, even if the stool sample is negative. Thus, it is an accepted practice to treat chronic diarrhea by administering a whipworm dewormer. Response to treatment indicates that whipworms were present but could not be detected on fecal examination.

"Any dog with chronic diarrhea should be suspected to have whipworms..."

How are whipworms treated?

Several medications are effective against whipworms. All medications must be repeated monthly for three months to clear the infection.

The most frustrating aspect of whipworm infections is the high re-infection rate because whipworm eggs are extremely hardy in the environment. Therefore, if a dog is diagnosed with a whipworm infection, it is advisable to treat it again every three to four months. The other option, which is much simpler, is to use a heartworm preventative that contains a whipworm medication.

Whipworms are far less common today than in previous years because of the widespread use of modern heartworm prevention products.