What is Giardia?

Giardiasis is an intestinal infection of man and animals caused by a protozoan parasite Giardia intestinalis (also known as Giardia lamblia).

Giardia is a simple one-celled parasitic species; it is not a “worm”, bacteria or virus.  The parasite occurs worldwide and is a common cause of “Traveler’s Diarrhea” in people. Outdoor enthusiasts who inadvertently consume contaminated water may develop “beaver fever”, which is another name for giardiasis in people. Other examples of protozoan parasites that can cause enteric (intestinal) disease are Coccidia, Cryptosporidia and Toxoplasma.

Giardiasis can be an important cause of illness, especially diarrhea, in animals and man. However, the majority of dogs infected with Giardia do not have diarrhea, vomiting or any other signs of illness.

The Giardia organism has two forms. A fragile, feeding form exists in the gut of infected animals, while a hardy cystic form is shed in feces and can survive several months in the environment, particularly in water and damp environments.

How do dogs get giardiasis?

A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. In susceptible dogs, once the cyst passes into the dog’s intestines; it goes through transformation to the trophozoite or feeding form and attaches to the intestinal wall to feed. If sufficient numbers are present, clinical signs of damage to the intestinal wall will develop. Trophozoites reproduce by dividing, and some transform into the cystic form. Eventually, the dog passes cysts in its stool. These cysts are immediately able to infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water.

When Giardia cysts are found in the stool of puppies and debilitated adult dogs, they may cause severe, watery diarrhea that may be fatal if left untreated. However, if cysts are found in a healthy adult dog without diarrhea the infection may be transient and treatment may not be necessary.

The likelihood of developing disease increases when large numbers of cysts are present in the environment from fecal contamination. Giardiasis is a common occurrence in environments that are densely populated, such as kennels, pet stores, or animal shelters.

What are the clinical signs of Giardiasis?

These microscopic parasites attach themselves to the intestinal wall and the damage causes an acute (sudden-onset) foul-smelling diarrhea. The stool may range from soft to watery, often has a greenish tinge to it, and occasionally contains blood. Infected dogs tend to have excess mucus in the feces. Vomiting may occur in some cases. The signs may persist for several weeks and gradual weight loss may become apparent. The diarrhea may be intermittent. Most dogs do not have a fever but may be less active. The disease is not usually life threatening unless the dogs’ immune system is immature or immunocompromised.

How is giardiasis diagnosed?

To diagnose a giardia infection, a fecal ova and parasite screen will be run.  A small amount (~2grams) of fresh feces (not more than 24 hours old) is needed to run the test.   This sample will be sent to a reference lab which uses two different testing process to determine if giaridia is present.  One is called centrifugal floatation with microscopic examination to look for parasite cysts.  If cysts are found then your dog is actively shedding at that time, however, this parasite sheds in cycles so the flotation test alone may miss an infection.  For this reason a different test called a Giardia specific antigen (cell proteins) test is also run and will detect infections even when you pet is not actively shedding the parasite.

How is giardiasis treated?

Giardia can occasionally be a difficult organism to kill, however in most cases the parasite can be eliminated after one course of treatment.  The first course of treatment is with a medication called fenbendazole.  This is a liquid medication that is administered orally once daily for 5 days.   A fecal sample should be tested 5 days after treatment is completed to ensure the parasite has been eliminated.  A second fecal sample testing 4 weeks after treatment is also recommended to ensure re-infection has not occurred.  If this first treatment is not successful then another medication called metronidazole can be added in combination with the fenbendazole for a second treatment.

Along with medication, stringent hygiene control, a high fiber diet, and environmental cleaning can aid in elimination of this parasite.  Fecal matter should be picked up immediately after the bowel movement has occurred.  Also, cleaning the hind end with a baby wipe after each bowel movement will prevent spread of cysts attached to the surrounding fur.  A head to toe bath of your dog should be done on the first and last day of treatment.  Make sure the chin and feet are washed thoroughly as higher concentrations of cysts have been found in these areas.  Adding fiber to your dog’s diet throughout the length of treatment may also help to decrease the parasites attachment to the gut wall.  To each meal it is recommended to add 1 tsp of Metamucil for every 11 -22lbs of dog.  Although the parasite is difficult to kill, washing all bedding and cleaning carpet/floors can help decrease the amount of cysts in the environment.  Temperatures over 60℃ will kill the parasites, so steam cleaning where able is an option to decontaminate the environment.

What is the prognosis for Giardiasis?

The prognosis is good in most cases. Debilitated or geriatric animals and those with incompetent immune systems are at increased risk for complications, including death.

Can my dog give a Giardia infection to me or my family?

Giardia can cause diarrhea in humans and some strains can be passed from dogs to humans. In the past, it was assumed that cats and dogs, along with wildlife, were an important source of infection for humans.However, human-to-human transmission is also important and contaminated municipal water supplies are responsible for many outbreaks.

If your dog is diagnosed with giardiasis, environmental disinfection and good personal hygiene are important to prevent accidental spread to humans. In particular, people with immunodeficiency, such as AIDS or cancer, or who are undergoing chemotherapy, should use extreme care, especially when handling feces or after administering medications.

How to keep my pet and family safe from intestinal parasites:

Although it is not necessary to routinely deoworm for giardia it is best practice to routinely deworm your dog for other parasites such as roundworm, hookworm and whipworm, some of which also have the potential to cause disease in people.  Along with a deworming protocol routine fecal ova and parasite screens are also advised at least on a yearly basis. This is to ensure that the deworming program is working and allows us to pick up infections such as giardia and coccidia that are not routinely included in deworming.  The frequency of deworming for your pet will depend on its age and lifestyle.  Your vet can help you to determine the best plan for your pet and your family.

Ernest Ward, DVM  (Modified by MAH jan/2106)

© Copyright 2009 Lifelearn Inc. Used and/or modified with permission under license.

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