Giardia of the Dog

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What is it?

Giardiasis is a parasitic infection of the small intestine caused by a flagellated protozoan called Giardia duodenalis. There are 2 stages, namely the trophozoite and the cyst. The trophozoite stage is within the intestine, whereas the cyst stage is shed in the feces and found in the environment. Trophozoites are fragile, whereas cysts are resistant in the environment and can survive for months. 

Where can it be found?

It can be found worldwide.

How does infection occur?

Transmission is via the fecal-oral route. Infected dogs pass infective cysts through their feces into the environment. Another dog can then become infected via ingestion of feces containing an infective cyst (direct contact), or ingestion of fecal-contaminated water or food containing an infective cyst (indirect contact). 

What are the clinical signs?

It is commonly asymptomatic (has no clinical signs) and many dogs are asymptomatic carriers. It may also present with mild self-limiting clinical signs. If there are clinical signs, the most common clinical sign is diarrhea, and possibly abdominal discomfort. Although rare, it can also cause vomiting and fever. Dehydration, lethargy, anorexia and weight loss can additionally be appreciated with significant infections. Young or immunocompromised patients are the ones who are usually more severely affected.

How is it diagnosed? 

Diagnosis can be made via fecal flotation or fecal smear, but is challenging due to the intermittent cyst shedding and the fragility of the trophozoite. Clinical signs can be present prior to cyst shedding, and repeat testing may be required. Healthy animals can shed cysts, and therefore shedding does not always indicate disease. ELISA (enzyme-linked immunosorbent assay), PCR (polymerase chain reaction), and DFA (direct immunofluorescence assay) are considered superior to fecal flotation or fecal smear. 

What are the treatment options?

The goal of treatment is to resolve clinical signs. It may be self-limiting and not require treatment, particularly with subclinical infections. However, even if subclinical, consider treatment when your pet is likely to spread the infection, particularly when an immunocompromised person is living in the home. If treatment is required, some of the medications your veterinarian may prescribe are called fenbendazole and metronidazole. Repeat treatment may be needed. If your pet is dehydrated, additional treatment such as IV fluid therapy may be needed. It is also recommended to bathe the patient to help decrease cysts and to additionally disinfect the environment which helps decrease reinfection. Elimination may be challenging due to the ease of reinfection. 

Follow-up fecal testing is recommended 24 to 48 hours following treatment if clinical signs have not resolved. Follow-up fecal testing asymptomatic patients is somewhat controversial. It is questionable whether or not to follow-up fecal test and/or treat if your pet is asymptomatic unless likely to spread the infection, particularly when an immunocompromised person is living in the home.

How can it be prevented?

Prevention consists of picking up feces promptly from the environment to help limit environmental contamination and spread of disease. Prevent your pet from coming into contact with another animal’s feces.

Can my dog infect humans or cats?

Zoonosis is controversial due to the various genetic assemblages of Giardia spp. They are typically known to be host-specific, and therefore dogs rarely infect humans or cats. It is recommended to be considered potentially zoonotic and to practice good hygiene, particularly in the young or immunocompromised populations. In humans, it is sometimes referred to as “traveler’s diarrhea”, “beaver fever”, or “Montezuma’s revenge”.

For Veterinary Professionals, refer to our app, VetpocketTM, for more in depth reference material including treatment dosing guidelines.

*Disclaimer: The information is not intended to replace clinical judgment or guide individual care in any matter. Please check any information and values prior to use and use at your own risk.