Helminths

By | 2011-08-04

Trichuris

Cause of Trichuris

Trichuris vulpis is perhaps one of the most common causes of chronic large bowel diarrhea in dogs. Cats are occasionally infected with Trichuris serrata and Trichuris campanula. Clinical signs in Trictouro-infected dogs and cats may vary from asymptomatic infections to mild intermittent episodes of mucousy feces to acute-onset bloody diarrhea with tenesmus and dyschezia.

Pathophysiologyof Trichuris

The fecal-oral route of transmission is the canonical route of infection. After ingestion of infective Trichuris ova, eggs hatch in the small intestine and larvae migrate to the cecum and colon where they attach to the mucosa. The pathogenicity of any infection is generally related to the magnitude of the host immune response. Factors contributing to the pathogenicity and clinical signs include the number of mature worms present, the location of the worms, the degree of inflammation, the severity of anemia or hypoproteinemia, nutritional status of the host, and the presence of other gastrointestinal parasites and micro-organisms.

Clinical examination

Affected animals generally have mild clinical signs of typhlitis and colitis, although some dogs develop a clinical scenario of signs and laboratory findings (e. g., hyponatremia, hypochloremia, hyperkalemia) consistent with hypoadrenocorticism. When tested, Trichuris-infected dogs are normoreactive to adrenocorticotropic hormone stimulation and are instead referred to as pseudo-Addisonian. Eosinophilia, anemia, and hypoalbuminemia are possible, but these are more common laboratory findings with other gastrointestinal helminth infections (e. g., hookworms).

Diagnosis of Trichuris

Trichuris ova can be identified on routine fecal flotation procedures; however, they may be missed because of intermittent shedding. Empiric treatment for occult Trichuris infection should always be performed before moving on to a more detailed, costly, and unnecessary medical investigation.

Treatment of Trichuris

Many safe and effective therapeutic agents are available for Trichuris spp. Fenbendazole, febantel with praziquantel, milbemycin, and ivermectin with pyrantel pamoate all have established efficacy against whipworms. Treatment should be repeated in 3 weeks and again in 3 months, and pet owners should be advised to decontaminate the environment.

Prognosis of Trichuris

The prognosis for recovery and cure is excellent.

Ancylostoma caninum

Hookworms are primary pathogens of the small intestine, but they occasionally infect the cecum and colon with overwhelming infestations. Diagnosis is achieved by demonstrating hookworm ova in the feces, and treatments are similar to those used for whipworm infections.

Heterobilharzia americana

Heterobilharzia americana: Cause

Heterobilharzia americana is considered the primary agent of schistosomiasis in dogs. It is an uncommon infection in dogs and is encountered almost exclusively in the southern Atlantic and Gulf Coast states in the United States. In addition to the dog, nutria, raccoons, rabbits, and mice serve as important reservoir hosts. Although uncommon, heterobilharziasis is an important consideration in the differential diagnosis of acute and chronic large bowel diarrhea in endemic areas.

Pathophysiology of Heterobilharzia americana

The life cycle of Heterobilharzia americana is complex and involves an intermediate (snail) and definitive (dog) host and various life stages. Dogs are infected when motile cercaria from snails penetrate their skin. The schistosomulae migrate from the skin to the liver of the definitive host, where they develop into mature male and female worms. Adult schistsomes lay eggs in the terminal mesenteric venules, and egg migration through the bowel wall elicits an intense granulomatous response. It is usually the host response that gives rise to the clinical symptomatology.

Clinical examination

Clinical signs vary from none to acute signs of vomiting, weight loss, bloody diarrhea, and progressive emaciation. Affected animals may have biochemical evidence of hypoalbuminemia, hyperglobulinemia, hypercalcemia, and liver enzyme elevation.

Diagnosis of Heterobilharzia americana

Diagnosis is confirmed by demonstration of ova on direct fecal examination or tissue biopsy. Serologic tests have not yet been successfully implemented in companion animals.

Treatment of Heterobilharzia americana

Fenbendazole in combination with praziquantel appears to be effective in the treatment of Heterobilharzia americana.

Prognosis of Heterobilharzia americana

The prognosis for acute infections is generally favorable, although severe liver involvement may portend chronic liver disease and cirrhosis.