Giardia and Tritrichomonas foetus: an update (Proceedings)

Nov 01, 2009


Giardia is a flagellate protozoan parasite commonly encountered in small animal veterinary practice. The most common clinical syndrome associated with Giardia is acute small bowel diarrhea, but in some cases acute large bowel diarrhea, chronic small or large bowel diarrhea, or rarely acute or chronic vomiting may occur. Studies throughout the world have found infection rates ranging from 1%-39% in pet and shelter dogs and cats. Recently a study utilizing PCR found 80% of cats in Perth Australia to be positive. Many of the Giardia infected animals did not have diarrhea. Younger animals had a higher rate of infection.

It appears that various strains posses differing degrees of pathogenicity. Clinical signs may be self-limiting in some patients. Severe disease may occur in puppies or kittens, animals with other gastrointestinal parasites or diseases, or debilitated animals, but also can occur in otherwise healthy patients. Giardia cysts are not routinely identified by commonly used fecal flotation solutions because cysts become shriveled and cannot be identified. In addition, the numbers of cysts shed in the feces fluctuate over time. Many commonly used anthelmintics are not effective against Giardia. Although the issue is presently unresolved, some strains of Giardia are a zoonotic threat. This paper will review the important clinical aspects of giardiasis and will present a practical diagnostic plan and differential diagnosis.

Infection is acquired by ingestion of cysts, only a small number are necessary. Most dogs and cats infected with Giardia remain asymptomatic. When clinical signs occur, acute small bowel diarrhea is most common. Small bowel diarrhea has the following characteristics: liquid to semi-formed feces, moderately increased frequency of defecation, and normal to increased quantity of feces per defecation. The presence of melena (digested blood) is uncommon in cases of giardiasis. Diarrhea usually is self-limiting in animals that develop clinical signs, and has been described as pale, malodorous, and fatty. Severe diarrhea may be accompanied by dehydration, lethargy, and anorexia. However, most affected patients remain bright and alert, afebrile, and maintain a normal appetite. Occasionally acute vomiting may accompany diarrhea. The author has endoscopically observed severe erosion of the duodenum in some cases that resolved following successful treatment for Giardia. A mild eosinophilia has been demonstrated.

Chronic small bowel diarrhea with weight loss, poor body condition, and intermittent vomiting may also occur. In addition, the author occasionally has identified Giardia in cases of chronic vomiting. Giardia may be found in dogs and cats that have other gastrointestinal diseases, especially inflammatory bowel disease. In these cases, the clinical signs and laboratory findings reflect the underlying disease. In humans, Giardia may mimic inflammatory bowel disease.

Acute or chronic large bowel diarrhea with hematochezia, excess fecal mucus, and tenesmus may occur on occasion. In cases of large bowel diarrhea, the frequency of defecation is moderately to greatly increased and quantity of feces per defecation in reduced. Excess fecal mucus is often seen in infected cats.