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 lining of those organs. Whipworm infection results in watery, 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 very resistant to drying and heat, so they can remain alive in the environment for up to 5 years. Once laid, they mature to an infective stage (a process known as embryonation) in the environment and are able to re-infect a new dog in 10-60 days. The mature eggs are swallowed by the dog, hatch, and then mature to adults in the lower intestinal tract, completing their life cycle (see illustration).

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 large bowel 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 is an indication that whipworms were present, but could not be detected on fecal examination.

How are whipworms treated?

There are several drugs that are effective against whipworms. All drugs require two treatments, spaced at a three to four week interval, to clear the infection.

The most frustrating aspect of whipworm infections is the high rate of re-infection, because whipworm eggs are extremely hardy in the environment. Therefore, if a dog is diagnosed with a whipworm infection, it is advisable to treat 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 widespread use of modern heartworm prevention products.

Can I get whipworms from my dog?

No. Whipworms are not infectious to people. They are exclusive parasites of the dog.