Giardia is a protozoan parasite found all over the world. It infects humans, many domestic animals and birds. Giardia lives in the intestinal tract and infection may be asymptomatic or can result in gastrointestinal symptoms.
Giardia infections (called Giardiasis) show no gender or breed predilection but are most common in young animals and in animals under close confinement, such as those in kennels, animal shelters and pet stores.
Most cases of Giardia infection in humans arise from person-to-person contact or from contaminated water, but animals do harbor strains of Giardia that are infectious to humans and animal-to-human transmission theoretically is possible.
What to Watch For
Flatulence (excessive gas)
Veterinary care should include diagnostic tests and subsequent recommendations. Diagnostic tests are needed to recognize Giardiasis and exclude other diseases. Tests may include:
Direct fecal smears to look for two different stages of Giardia organisms called “cysts” or “trophozoites.” A positive direct smear results in a conclusive diagnosis of Giardiasis, but direct fecal smears may be negative in infected animals.
A zinc sulfate concentration test to identify Giardia cysts.
An enzyme-linked immunosorbent assay (ELISA) test to identify Giardia antigens in the stool.
Direct immunofluorescence test to identify Giardia cysts in feces.
Collection of samples from the duodenum (first part of the small intestine) during endoscopy and examination for Giardia trophozoites.
Treatment for pets with Giardia infection may include one or more of the following drugs:
A combination of praziquantel, pyrantel and febantel
Home Care and Prevention
Administer as directed all medications prescribed by your veterinarian. All of the prescribed medication should be given to ensure elimination of the infection. A high-fiber diet may improve stool consistency in pets with diarrhea associated with Giardia infection.
Decontamination of the environment is an important part of preventing infections. In multiple-dog households and in situations in which animals are under close confinement (e.g. kennels, animal shelters, pet stores), proper sanitation is crucial to prevent cross-contamination from one animal to another. All fecal material must be removed from cages, runs and yards. Kennels must be cleaned with appropriate disinfectants and totally dried before allowing pets access to them.
All animals should be treated with appropriate medication before being introduced into a multiple-animal environment.
Bathing animals before introducing them into an uncontaminated environment allows for removal of feces and infective cysts from the hair coat.
Pet owners should remove feces from the yard, avoid allowing their dog to drink from streams and lakes, and regularly bath the animal to remove any feces from the hair coat.
The protozoan parasite Giardia occurs in two forms. The active (motile) form that lives and multiplies in the intestinal tract is called a “trophozoite.” It can be recognized under the microscope by its characteristic appearance, which looks somewhat like a monkey face with two eyes and a nose. The trophozoite only lives in the intestine and cannot survive in the environment for any significant length of time. The other form is called a "cyst" and is the infective form of the parasite. Each cyst contains two completely formed trophozoites inside of it. Cysts can remain viable in the environment for many months and can cause infection if conditions are cool and moist.
Dogs are infected by ingesting cysts in the environment. Most infections arise from contaminated water, such as puddles, streams, lakes, shallow wells and water contaminated by feces.
Giardia causes disease by damaging the small intestine, which leads to maldigesion (inability to break down nutrients properly) and malabsorption (inability to properly absorb digested nutrients). Giardia also increased intestinal motility, thus decreasing the amount of time the intestine can digest and absorb nutrients. Increased intestinal motility may be manifested by flatulence (excessive gas production) and diarrhea.
The most common symptom of Giardia infection is diarrhea but there are many other causes of diarrhea. Some examples include:
Dietary disturbance: sudden changes in diet, overfeeding, dietary indiscretion (like getting into the garbage and eating too many table scraps)
Drugs: aspirin and similar non-steroidal anti-inflammatory drugs such as ibuprofen; many antibiotics; anti-cancer drugs; heavy metals (lead, arsenic); insecticides
Other parasites including worms (hookworms, roundworms, whipworms, tapeworms), and protozoa (coccidian, Entamoeba, Trichomonas, Balantidium)
Viruses: parvovirus, coronavirus
Bacteria: Salmonella, Campylobacter, Clostridium, E.coli
Obstruction of the intestinal tract by foreign bodies
Tumors of the intestinal tract
Mechanical obstruction of the intestinal tract caused by volvulus (twisting of the intestine) or intussusception (telescoping of the intestine on itself)
Metabolic disorders such as kidney failure, liver failure and hypoadrenocorticism
Diagnostic tests are needed to identify giardiasis and exclude other diseases. Tests may include:
A complete medical history and a thorough physical examination. Specific diagnostic tests will be needed for your veterinarian to diagnose giardiasis in your pet
Direct examination of a fecal smear under the microscope. The trophozoites are more likely to be seen in diarrhea and the parasite can be recognized by its rapid forward motion. Cysts are more likely to be found in semi-formed feces. It takes considerable expertise to be able to recognize cysts.
Fecal enzyme-linked immunosorbent assay (ELISA) test to detect substances given off by the trophozoites in feces. Your veterinarian may be able to perform this test in the office or may send a fecal sample to a laboratory that conducts this test.
Zinc sulfate concentration test. A fecal sample is mixed with a zinc sulfate solution and, after a few minutes of processing, Giardia cysts (if present) will float to the top of the solution where they can be collected and identified under the microscope. If this test is performed on three separate fecal samples from the same dog, it will detect Giardia more than 96 percent of the time in infected animals.
Several drugs have been used to treat Giardia infections in pets. Anti-parasitic drugs are the most important part of treatment, but additional measures such as adding fiber to the diet can improve stool consistency and hasten your pet’s recovery. Specific treatments include:
Metronidazole is an antibiotic that has been widely used to treat Giardia in dogs as well as in people. This drug has reasonable efficacy against Giardia and has the added advantage of being effective against other parasitic protozoa and some bacteria that may also have contributed to the diarrhea. Adverse effects on the nervous system have occurred with high doses.
Fenbendazole is a de-worming medication that kills common parasitic worms such as hookworms, roundworms and whipworms. When given at the usual dosage, fenbendazole is also very effective against Giardia. Fenbendazole is very safe.
The combination of praziquantel, pyrantel and febantel is another de-worming medication used against parasitic worms, such as hookworms, roundworms, whipworms and tapeworms. Recent studies show that it also is effective against Giardia. Treatment only has to be given for three consecutive days. The drug, however, is somewhat expensive.
Optimal treatment for your pet requires a combination of home and professional veterinary care. Administer any medications prescribed by your veterinarian and notify your veterinarian if you are experiencing problems treating your pet.
Follow dietary changes recommended by your veterinarian such as increasing the fiber content of the diet. Follow specific recommendations for controlling the disease such as decontaminating the environment, keeping your pet’s hair coat clean and avoiding reinfection by preventing your pet from drinking from puddles, lakes, streams and other sources of stagnant water.
After finishing treatment, submit a fresh fecal sample to your veterinarian to confirm effective treatment. If, after several days of treatment, no improvement is noted, return your pet to your veterinarian for re-evaluation.