Whipworms in Dogs

Whipworms are among the “unholy trinity” or infectious agents in dogs—including roundworms and hookworms. For many reasons, including persistence of infectious stages in the environment, it is advantageous to prevent these parasitic infections and the resulting contamination in the soil.¹ Trichuris vulpis whipworms are the third member of the unholy trinity but the one that people seem to consider the least.² Although whipworms in dogs receive the least “respect” of the common gastrointestinal nematodes of dogs, there is a very good chance that you will diagnose them.

The Whipworm Life Cycle

Whipworms are named for their whiplike appearance, a thin anterior end (esophagus) and thick posterior end (reproductive portion). Adults live primarily in the cecum but also in the large intestine in heavy infections. As with roundworms, adult whipworms produce environmentally resistant eggs, which are extremely difficult to destroy. These eggs contain a single cell, which develops to infective first-stage larvae (L1) inside the egg in approximately 1 month. After a dog ingests eggs containing infective L1, the larvae will develop into reproductively mature adults after approximately 3 months.² Unlike roundworms, whipworms do not migrate outside of the intestinal tract; therefore, there is no somatic migration into tissues, no migration of larvae to pups in utero, and no transmammary transmission. Because of the long prepatent time, whipworms are normally diagnosed in dogs older than 6 months.³

Clinical Disease

Adult whipworms burrow their anterior end into the intestinal mucosa. This burrowing causes hemorrhage and irritation secondary to the subepithelial movement of adult worms during feeding. The severity of disease is related to the number of worms—the larger number, the more severe and debilitating the disease. A large enough number of whipworms can lead to death.²

The clinical signs of infection are those that commonly accompany large bowel diarrhea, mucoid and/or bloody. Also, tenesmus and weight loss may be observed with no bloody diarrhea. It has also been documented that severe whipworm infections can mimic hypoadrenocorticism (Addison’s disease).⁴ In these cases, one may neglect to consider whipworms as a differential diagnosis, but they could be the most likely etiology.³

Diagnosis of Whipworms in Dogs

Sometimes whipworm infection may be suspected on the basis of clinical signs without whipworm eggs being seen on fecal flotation. Diagnosis by fecal flotation can be difficult for 2 key reasons: 1) the eggs are shed intermittently or in low numbers, and 2) the eggs do not float well. Whipworm eggs are considered to not float well because they are heavier than hookworm and roundworm eggs; the specific gravity of whipworm eggs is 1.15, compared with that of Ancylostoma caninum (1.05) and Toxocara canis (1.09) eggs. Although T. vulpis eggs should float in most standard flotation solutions, a centrifugal float using Sheather’s sugar solution (specific gravity 1.25 to 1.30) will provide the best chance for diagnosis (FIGURE 1). In recent years, tests have become available that detect T. vulpis antigen in feces even before egg shedding has begun. These tests can be used as supplemental tests for patients with clinical signs but no eggs apparent on fecal flotation.^2,3

Figure 1. Trichuris vulpis eggs (magnification x40). Photo courtesy of Dr. Gui Verocai, Texas A&M University.

Treatment of Whipworms in Dogs

Because of the 3-month prepatent period, during which immature whipworms are not susceptible to anthelmintics, treatment administration spans 3 months. Treatment of T. vulpis worms is accomplished by 1 of 4 regimens:

1. Fenbendazole (50 mg/kg) q24h for 3 days at the time of diagnosis, 3 weeks after diagnosis, and 3 months after diagnosis.
2. Fenbendazole (50 mg/kg) q24h for 3 days monthly from the time of diagnosis to 3 months after diagnosis.
3. A heartworm preventive labeled for treatment of T. vulpis monthly for 3 months; ideally, however, the pet would receive this preventive over the long term.^2,3
4. A single monthly dose of a praziquantel/pyrantel pamoate/febantel combination from the time of diagnosis to 3 months after diagnosis.

Zoonotic Potential

The zoonotic potential of T. vulpis worms has been debated. However, it is generally accepted that the zoonotic potential is very low, especially when compared with that of hookworms and roundworms
of dogs.²

Prevention of Whipworms in Dogs

Key to development of severe disease is environmental contamination; because the eggs are resistant, they can accumulate in the environment and therefore be ingested in large numbers. Ideally, it is more prudent to prevent contamination by instituting appropriate control measures before the worms can contaminate the environment.

The Ben Franklin quotation, “An ounce of prevention is worth a pound of cure,” can apply to whipworm infections. This preventive ounce can be condensed for clients into the same 3 simple points to prevent whipworms as well as roundworms and hookworms:

1. Pick up dog feces promptly. If T. vulpis eggs are not in the environment, other animals cannot become infected. Follow this practice at your clinic, and convince your clients to do it at home.
2. Cover sandboxes. Covered sandboxes cannot become contaminated by stray dogs.
3. Perform regular fecal examinations, and regularly deworm animals (as described above).

Emphasizing prevention information to clients in a concise, bullet-point format will help them understand and adhere to the recommendations. Client adherence can markedly reduce the risk for whipworm infection of pets. If you emphasize only one point, it should be that one easy way that clients can control whipworms is to routinely pick up their dog’s feces. Sometimes environmental contamination is outside of the client’s control, such as at dog parks. For these situations, regular fecal examination and treatment or monthly administration of a preventive are recommended.