Parasitic Diarrhea (Giardiasis) in Dogs

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Last updated on
3 min read

Key takeaways

Giardiasis is an infection caused in dogs by species of Giardia, a microscopic protozoan parasite.

  • Giardia pass in host fecal matter and contaminate dirt, water, fur, and other surfaces, allowing for infection of dogs in contact with contaminated environments
  • Infections are more common in densely populated areas, such as kennels or dog parks, and in rare cases can pass from pet to owner
  • Keeping a dog, their living space, and their play space clean greatly reduces the likelihood of infection
  • Most infected dogs show no symptoms, and with proper hygiene, cross-infection is unlikely
  • When present, symptoms include vomiting, diarrhea, or weight loss and warrant prompt medical attention
  • Diagnostics include physical examination, bloodwork, and a fecal analysis
  • Infections are treated with anti-parasitic medication
  • Prognosis is generally good, although recurrence is possible if preventative hygiene measures are not taken
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A closer look: Parasitic Diarrhea (Giardiasis) in Dogs

Giardiasis is a common canine condition, although most dogs living in sanitary living environments are far less susceptible to infection. Giardiasis usually causes no symptoms and is not a cause for medical concern, although protozoa can pass from pet to owner in rare cases. Any symptomatic dog requires prompt veterinary assistance to control the infection.

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Risk factors

In most cases, giardiasis is asymptomatic. Symptoms may only be visible in young or immunocompromised animals who become severely infected.

Dogs that are exposed to many other animals, are very young, or are immunocompromised, are most at risk of developing an infection.

Possible causes

Giardiasis protozoa are small parasites which pass with the fecal matter. Other dogs which come into contact with areas contaminated with fecal matter such as soil, infected dogs, or water may become infected by ingesting the parasite directly. Once ingested, protozoa migrate to the intestines and proliferate until they pass with stool and continue the cycle.

Main symptoms

Testing and diagnosis

Diagnostics include:

  • A physical examination
  • Bloodwork
  • Fecal analysis

Steps to Recovery

Giardiasis is rarely symptomatic, and an infected animal may not always require treatment. In younger or symptomatic animals, giardiasis is treated with anti-parasitic medication. Repeat follow-up visits to a vet may be necessary to track recovery and ensure that all parasites have been eliminated.

Protozoa can survive for long periods of time outside of their host, and medication only targets protozoa inside the body and does not prevent re-infection. Recurrence is possible, especially if a dog has continued access to a contaminated area. With appropriate cleaning measures and anti-parasitic medication, most dogs recover successfully from infection with a good prognosis.


Proper hygienic care and sanitary practices are essential to preventing a giardiasis infection. Prompt removal and disposal of feces, as well as cleaning and disinfecting of play and living areas greatly reduce the likelihood of contracting an infection.

Regular bathing washes existing parasites from the fur, further reducing the odds of becoming infected.

In some countries, a vaccine for giardiasis is available, although the efficacy is poor.

Is Parasitic Diarrhea (Giardiasis) in Dogs common?

Giardiasis is common in dogs, and is more common in densely populated areas, such as a kennel or dog park. Puppies are also more susceptible.

Typical Treatment

  • Anti-parasite medication.
  • Bathing


No Author - Writing for Companion Animal Parasite Council
Lucy J. Robertson, , PhD - Writing for Merck Veterinary Manual
Sharon Patton, , MS, PhD / Peter D. Constable , BVSc (Hons), MS, PhD, DACVIM - Writing for Merck Veterinary Manual
Wendy Brooks, DVM, DABVP - Writing for Veterinary Partner
Matt Brewer, DVM, PhD, DACVM (Parasitology) - Writing for Today's Veterinary Practice

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