GIARDIA

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Gastroenterology & Digestive Diseases -  General Practice & Preventative Medicine

Giardia is a flagellated protozoan parasite found all over the world that can affect humans, mammals and birds. The parasite lives in the small intestinal tract and causes damage to the intestines. Although most cases of human Giardia point to other sources of infection (person-to-person contact or contaminated water), animals do harbor strains of Giardia that are infective to humans, and animal-to-human transmission is theoretically possible.

The Giardia parasite occurs in two forms. The active, motile form that lives and multiplies in the intestinal tract is called a trophozoite. Under a microscope this form has a characteristic pear shape with a "smiley face" appearance. The trophozoite lives only in the intestine and cannot survive in the environment for any significant length of time. The second form is the cyst, which contains two completely formed trophozoites. This is the infective form. Cysts can remain infective in the environment for many months, especially if conditions are cool and moist.

Giardia causes disease by attaching to the intestinal epithelial cells and damaging the small intestine, which then leads to malabsorption. Giardia also causes increased intestinal motility, shortening the amount of time the intestinal tract has for digestion and absorption of the nutrients.

DIAGNOSIS OF GIARDIA

ETIOLOGY AND RISK FACTORS

• Causes - Dogs and cats become infected by eating cysts from the environment. Most cases are from contaminated water, such as puddles, streams, lakes, shallow wells and fecal-contaminated water.
• Risk factors
• Age - No known risk, although Giardia is seen most commonly in young animals.
• Breed/genetics - No known risk
• Sex - No known risk
• Geographic/environmental - Cool and moist conditions are preferable for the cysts and allow the cyst to remain viable for an extended period of time in the environment. Giardia is most often found in areas where animals are kept confined or in groups, such a kennels, shelters and pet stores.
• Other medical disorders - Concurrent infection with other gastrointestinal parasites can worsen the signs associated with Giardia.

• Prevention - Prevention involves four main approaches:
• Decontamination of the environment. In multiple dog households and in crowded situations such as kennels, shelters and pet stores, proper sanitation is key to preventing cross contamination from one animal to another. All fecal material needs to be removed from cages, runs and yard. Kennels need to be cleaned with proper disinfectants and should be totally dry before allowing animals into them.
• Treatment. All animals should be treated with appropriate medication before being introduced into a multi-animal environment.
• Shampooing. Bathing animals before introducing them into an uncontaminated environment allows for removal of feces and infective cysts from the hair coat.
• Prevent reinfection. Pet owners should remove feces from their yard, prevent their dog from drinking from streams and lakes, and bathe their dog regularly to remove any feces from the hair coat.
  
  A vaccine designed to aid in the prevention of disease caused by Giardia has recently been marketed (GiardiaVax).

HISTORY AND CLINICAL SIGNS

• Species affected - Dogs and cats
• Presenting signs and historical problems - Diarrhea is the most common sign of infection. Most often, the diarrhea is voluminous, malodorous, light-colored and watery. Some animals may also vomit, and some may show weight loss secondary to the diarrhea, although appetite is rarely affected. Flatulence may occur due to increased intestinal motility caused by the parasite. Many animals infected with Giardia are asymptomatic.

PHYSICAL EXAMINATION FINDINGS

Physical examination is often normal for animals with Giardia. Young animals are more likely to show clinical signs of diarrhea and weight loss.

DIAGNOSTIC STUDIES

• Clinical laboratory tests
• CBC - The complete blood count is usually within normal limits
• Serum biochemical tests - The biochemical tests are within normal limits.
• Urinalysis - The urinalysis is within normal limits
• Serology/immunologic tests - Fecal ELISA test kits are special tests that were originally developed to detect trophozoite in the feces. This test appears to be very accurate.
• Parasitology - Direct analysis of the feces can sometimes lead to a quick diagnosis. The trophozoites are more likely to be seen in loose feces and may be recognized by their rapid forward motion. Direct fecal smears often are a low diagnostic yield. Cysts are often difficult to see on direct smears.
  
  Zinc sulfate flotation is considered the best test. Performing this test on three separate fecal samples from the same animal detects Giardia cysts in infected animals greater than 96 percent of the time.

DIAGNOSIS AND PROGNOSIS

• Differential diagnosis - The most common symptom of Giardia infection is diarrhea, although there are many other possible reasons for diarrhea including:
• Sudden changes in diet
• Overfeeding
• Dietary indiscretion
• Drug induced causes such as non-steroidal anti-inflammatory medications, antibiotics, anti-cancer drugs, heavy metals (lead, arsenic), and insecticides.
• Other parasites such as hookworms, roundworms, whipworms, tapeworms, coccidia and entamoeba.
• Viruses such as parvovirus and coronavirus
• Bacteria such as Salmonella, Campylobacter, Clostridium and E.coli.
• Intestinal foreign bodies
• Kidney failure
• Liver failure
• Pancreatitis
• Recommended tests - CBC, biochemical profile, urinalysis, direct fecal examination and fecal floatation with zinc sulfate.
• Summary of diagnostic criteria - Fecal examination usually reveals the Giardia trophozoites or cysts. Fecal ELISA should be performed if zinc sulfate tests are negative and Giardia is still a possibility.
• Prognosis - The prognosis for Giardia infection is fair to good with appropriate treatment and management.

TREATMENT OF GIARDIA

TREATMENT PRINCIPLES

INITIAL/HOSPITAL THERAPY

Most animals are treated on an outpatient basis. For those animals with vomiting, weight loss and dehydration, hospitalization with intravenous fluids and antiemetics may be necessary.

LONG TERM/HOME THERAPY

Several drugs have been used to treat Giardia infections, although no medication is 100 percent effective in clearing Giardia and reoccurrence of clinical disease is not uncommon. Antiparasitic drugs are the mainstay of therapy; however, additional measures, such as adding extra fiber to the diet, and environmental and animal decontamination are important.

• Metronidazole (25 to 30 mg/kg orally twice daily for 5 to 10 days) has been used extensively to treat Giardia in dogs and cats, as well as in people. This drug has reasonable efficacy, and has an added advantage of being effective against other protozoans and some bacteria that might also be contributing to the diarrhea. Unfortunately up to 30 percent of infections are resistant to metronidazole.
• Fenbendazole (50 mg/kg orally once daily for 3 to 5 days) can be effective in treating Giardia.
• Albendazole (25 mg/kg orally twice daily for 2 days in dogs and 5 days in cats) is effective, but the side effect of profound bone marrow suppression precludes its use.
• Furazolidone (4 mg/kg orally twice daily for 5 days) has been shown to be effective in cats.
• Praziquantel/pyrantel/febantel (Drontal Plus) is a combination dewormer that treats hookworms, roundworms, whipworms and tapeworms. Recent studies show that it is effective against Giardia as well.
• Vaccination. There are some reports that vaccination of infected animals may result in clearing of the organism.

FOLLOW-UP CARE

Following treatment, a fecal sample should be examined to make sure treatment was effective.

Considerable controversy exists as to the potential for animals to spread Giardia to humans. There is scant evidence linking human infections to dogs and cats. Human cases of Giardia are usually caused by person-to-person contact or by drinking contaminated water. Until these controversies are resolved, it is best to err on the side of caution and treat all infected animals whether or not they are experiencing symptoms.