Whipworms

Trichuris vulpis infestation is one of the most common causes of acute or chronic large bowel diarrhea in dogs.^2,13 Puppies and dogs that live in contaminated environments are com­monly affected and often reinfected.

Clinical signs

Diarrhea with hematochezia and excess mucus occurs fre­quently. Abdominal pain, vomiting, inappetence, and weight loss can also be observed.¹⁴ The diarrhea may be intermittent in chronic cases. Anemia can result in pale mucous membranes and lethargy.

Pathophysiology

The parasite’s life cycle is direct. Adult worms shed eggs inter­mittently, which can result in false-negative fecal examina­tions. The eggs have thick, yellow-brown shells, are barrel­shaped, with polar plugs, and are approximately 80 ? 35 μm (Figure 6.3). Whipworm eggs can persist for years in the envi­ronment, but prolonged sunlight will kill them. Areas that can­not be easily cleaned, such as lawns and dirt kennels, can be­come contaminated, providing a source for reinfection. Under optimal environmental conditions, the eggs embryonate in as few as 10 days. After a dog ingests the infective eggs, the larvae

Figure 6.4:

Whipworms. Endoscopic appearance of adult whipworms (arrows) in the ascend­ing colon of a dog.

hatch in the small intestine and burrow into the mucosa for 2-10 days, emerge again, and attach to the mucosa in the ce­cum and ascending colon, where they complete their matura­tion.¹⁴ Female worms begin producing eggs 70-107 days after the infection has been acquired. Estimates of daily egg produc­tion range from 1,000-4,000. Adult worms may live up to 18 months.

Pathogenicity is related to the tunneling of the thin anterior portion of the adult worm into the epithelium of the cecum or ascending colon, producing localized inflammation, mu­cosal hyperplasia, and in some cases focal granulomatous reac- tions.^14,15 Adult worms measure 45-75 mm in length (Fig­ure 6.4).

Many infected dogs will not show any clinical signs. The fac­tors contributing to the development of clinical signs include the number of worms present, the location of worms, degree of inflammation produced, level of anemia or hypoproteine­mia, nutritional status of the host, and the presence of other GI parasites.¹⁴

Although infrequent, infections of human beings with Tri- churis vulpis may occur.^14,15 Clients should be warned of the possible public health significance and appropriate sanitary measures should be taken when disposing of fecal material.

Diagnosis

Whipworm eggs can be identified using routine fecal flotation procedures. Zinc sulfate flotation (with centrifugation) has been demonstrated to be more sensitive than other flotation techniques for identifying whipworm eggs.¹⁶ However, if multiple fecal examinations fail to identify eggs, treatment for whipworms should be instituted prior to performing addi­tional diagnostic tests. A presumptive diagnosis of whipworm infection can be made if clinical signs improve within 2-3 days of appropriate anthelminthic therapy. Adult worms may be seen in the cecum and ascending colon during colonoscopy if a dog with an occult infection has not been treated prior to performing colonoscopy (Figure 6.4).¹⁷ Eosinophilia may be present. Anemia and hypoproteinemia may develop in cases with severe infestation.

Treatment

There are numerous therapeutic agents that are effective against whipworms in dogs.¹⁵ Commonly used treatments in­clude fenbendazole (Panacur® at 50 mg/kg PO q 24 h for three days) and a combination of febantel, pyrantel pamoate, and praziquantel (Drontal® Plus at 25 mg/kg febantel PO once).¹⁸

Fenbendazole is a safe and efficacious drug with broad-spec­trum activity against common GI nematodes, Giardia, and some tapeworms.

Treatment should be repeated after three weeks and again after three months. The effects of most anthelminthics on the larval stages of whipworms remain unknown.¹⁴ After anthelminthic administration has removed the adult worms, larvae still de­velop into adult parasites and may reestablish infestation. Fre­quent disposal of feces will help reduce the risk of reinfection. In severe, recurrent cases, heartworm prophylaxis with milbe- mycin oxime (Interceptor® at 0.5 mg/kg PO q 1 month) will help control the whipworm infection.¹⁹

Prognosis

Clinical signs rapidly resolve following appropriate therapy. Reinfestation is common in dogs that live in contaminated environments.

6.4.2