Giardia in Dogs – Giardiasis, Symptoms, Causes, Diagnosis, Treatment & Prevention

Monday, October 9th 2017. | Dog treatment

Giardiasis: Everything You Should Know About It. For many dog owners, ‘Giardia’ doesn’t ring a bell. Diarrhea does though. But it brings an avalanche of unpleasant memories. Well, Giardia, diarrhea, and a couple other undesirable health signs, sometimes have a relationship.

And if they’re having a merry-go-round in your dog, then it’s bad news. This article arms you with important facts and vital information about Giardia (and Giardiasis) that you simply can’t be oblivious of.

Giardia in Dogs – Giardiasis, Symptoms, Causes, Diagnosis, Treatment Prevention

Let’s start with…

Giardia: The nasty bug causing all the ruckus

It may be nasty but it isn’t shy. Giardia is everywhere. Literally!

To put it simply, giardia is one of the many microorganisms that like to call the intestine home, and don’t play nice.

For those who have a fair bit of knowledge about biology, giardia is a flagellated protozoan parasite. The Giardia genus is diverse, with multiple species categorized into three major morphological groups. They inhabit the intestines of many animals, from amphibians to humans.

In fact, giardia is the most common intestinal parasite found in humans, causing the common “Traveler’s Diarrhea.”

The specie referred to when discussing giardia in dog, cats, and humans is Giardia duodenalis. It is a specie complex, which means it has several subtypes, subspecies, strains, or genotypes (called assemblages).There are seven G duodenalis assemblages lettered A to G.

Assemblages C and D have distinct preference for dogs. F prefers cats. However, assemblages A and B don’t have favorites and can take a spot in the intestines of humans as well as domestic animals.

Giardiasis: The disease

Giardia is the parasite, while Giardiasis is the disease caused by the parasite infecting a host. Giardiasis goes by many different names—Giardosis, Parasitic Diarrhea, Beaver Fever (especially in humans), Canine Giardia Infection, Lambliasis, and Lambliosis.

Is giardia in dogs contagious to humans?

As a species, G duodenalis is zoonotic, meaning it can make both humans and animals ill. But with different subtypes primarily targeting dogs and humans, a dog-to-human Giardia transmission is incredibly rare.

Incredibly rare isn’t a synonym of impossible though. The risk exists, albeit low, as some sources maintain that:

  • genotype A can infect dogs, cats, and humans; and
  • genotype B can infect dogs and humans

Some studies have found human giardia assemblages in dog feces. You don’t want to take any chances, so protect yourself by limiting exposure to Giardia when your dog is infected.

That said, you are more likely to get infected via human-to-human transmission. Especially via contaminated municipal water supplies, which have been responsible for many outbreaks.

In any case, individuals with weakened immune systems—say someone with AIDS or cancer—should exercise extreme care when tending to a dog with giardiasis.

What about to other animals?

Between animals, the chances of transmission are higher. Having your vet check other pets (domestic and/or exotic) for giardia is a good idea. If you have other dogs in the family, then testing them isn’t up for debate.

Causes and transmission: How dogs get giardiasis

Lifecycle of giardia

Giardia has two forms—a hardy, inactive cyst and a mature, active (feeding) trophozoite.

The form that exists freely in the environment is the cyst. Cysts are so hardy (resistant); they can survive for up to three months in the environment. They prefer moist, cool environments, living the longest in cold water.

Cysts are infective. When a suitable host ingests them, say your dog lapping up contaminated puddle water, they travel down the gut and settle in (stay free or attach to) the small intestine. Where they develop into trophozoites.

Trophozoites multiply by dividing into two (binary fission). Some eventually transform into cysts (the process is called encystation) as they transit towards the colon. Inevitably, the cysts end in the host’s feces that contaminate any surface it gets in contact with.

In dogs, the period from ingestion of cysts to passage of cysts in feces (poop) is 5 to 13 days.

Transmission of giardia

Giardia spread through contact with cyst-infected feces, either directly or indirectly via contaminated sources. For example, a giardia-positive dog may lick his backside and then leak another dog, cat or human. Thus, transmission is said to follow the fecal-oral route.

Your dog may become infected by:

  • Getting in contact with infected poop from another dog
  • Putting something in his mouth that is contaminated, for example eating grass or chewing on a stick
  • Playing and rolling in contaminated soil
  • Licking his body after getting in contact with a surface that is contaminated (say a dirty cage or litter box)
  • Drinking from a contaminated puddle, pond, or creek

Dogs more at risk of an infection transforming into a debilitating disease

Giardia can infect all dogs. But healthy adult dogs are less at risk of becoming ill from an infection. Dogs more likely to become ill and exhibit symptoms and signs of giardiasis include:

  • Puppies
  • Older dogs
  • Dogs with compromised immune systems
  • Prevalence of giardiasis
  • Up to 50% of puppies develop canine giardia infection
  • In shared living spaces, such as a kernel or shelter, up to 100% of dogs may develop Giardosis
  • Giardiasis is common across America and could infect dogs at any time of the year

Symptoms and signs of giardiasis: How you know your dog is infected

What does giardia do in the intestines of dogs?

In the intestine, giardia trophozoites impair the absorption of water, electrolytes, and nutrients; and damage the lining of the intestine. All of which lead to the following symptoms and signs:

  • Diarrhea; stool (poop) are soft to watery, poorly formed, frothy, appear pale, smell badly, contain mucus and may contain blood. Diarrhea is the most common symptom, reason why giardiasis is also called parasitic diarrhea.
  • Occasional vomiting
  • Possible weight lossor lower weight gain
  • Undernourishment
  • Lethargy (lack of energy)
  • Poor hair coat
  • Gas; stomach swells and looks bloated
  • In extreme cases, premature death

Occurrence of symptoms

As noted above, most healthy dogs infected with Giardia do not become ill. They do not show symptoms (are asymptomatic). Still, they would pass cysts and could infect other dogs.

When symptoms appear, especially in animals at higher risk, they may be:

  • acute (sudden)
  • transient (temporary)
  • intermittent (non-continuous); and so may mislead owners to assume their dog had something (or meal) he shouldn’t have
  • chronic (ongoing); at which point you’ve prolly speed-dialed your vet

In addition to these symptoms, Giardia may be at the root of chronic gastrointestinal (GI) inflammation, inflammatory bowel disease (IBD), and other digestive issues.

Diagnosis: How vets diagnose giardiasis

Your vet would test a sample of your dog’s poop to identify Giardia cysts or specific antigens (cell proteins).


Fecal smear and flotation tests

The two common tests used to diagnose giardiasis are the

  • fecal smear test; where your dog’s feces is directly smeared on a slide and viewed under a high-res microscope
  • fecal float test; using centrifugation-flotation technique with zinc sulfate

Vets use both tests to identify giardia cysts.

However, dogs do not shed cysts consistently. As such, it is entirely possible for a test result to return negative when your dog is indeed infected. In fact, the chance of detecting a cyst in a single fecal sample is only 70%.

To increase chances of detection, vets routinely perform the test multiple times within a short time. Stats show that testing three fecal samples within five consecutive days improves the chance of detection to over 90%.

ELISA test

Instead of testing for whole cysts, vets may send a fecal sample to the lab to test for specific giardia antigens (proteins released by giardia). This test (actually a chemical assay) is the ELISA test and its detection rate is higher at 95%.

If your dog suffers from chronic diarrhea, then insist on a fecal antigen (ELISA) test in addition to a regular smear or flotation test.

Treatment: How Giardiasis is treated

The treatment plan for giardia in dogs involves medication and bathing. You can’t get the drugs over the counter, they must be prescribed. And treatment can proceed on an outpatient basis. You only have to follow exact vet instructions for drug administration and bathing.


The drugs commonly used to combat giardia are fenbendazole (mainly) and metronidazole. Your vet may prescribe them singly or in combination and you’d have to administer the recommended regimen for 3-10 days.

There are no reports of side effects. And they are safe for pregnant and lactating (secreting milk) pets.


Bathing is necessary to remove giardia cysts from the hair coat of your dog. Your vet would recommend an acceptable frequency (how often you’d bathe your dog).

You’d have to wear a glove when bathing your dog. While bathing your dog, you’d have to ensure that you focus last on his rear end.

Additional measures to take

  • Observe your dog and give him copious amounts of water to counteract dehydration (caused by diarrhea).
  • Also place him on a low-residue, highly digestible diet to help lessen soft stools (caused by diarrhea) during treatment.
  • Disinfect your dog’s bowls, toys, beddings, and other belongings; carpeting and upholstery; and hard surfaces in your home (including your pet(s)’ living and sleeping areas).
  • Giardia doesn’t dig dry, warm environments. For instance, while it can survive for up to 7 weeks in cold soil, it can only survive in soil at room temperature (around 77°F) for only about 1 week. As such, letting a surface dry out after disinfection is good practice.

How long does it take to get rid of giardia?

There is no concrete time limit. Vets typically carry out repeated follow-uptests on all treated dogs two to four weeks after completion of treatment. Depending on the severity of infection, these follow-up tests may extend to monthly tests for up to 4 months after completing treatment.

These are cautionary tests to ascertain that your dog is free of giardia. The immediate follow-up tests are fecal float tests to identify cysts. ELISA tests may only be conducted after several negative float tests, as antigens take a long time to clear from your dog’s system. An ELISA test for a treated dog can show positive for up to 6 months after treatment.

Prevention: Protecting your dog from Giardia

  • Pick up after your dog when he defecates and disinfect surfaces daily. Remember to follow basic hygiene practices.
  • Do not let your dog eat his own feces or that of another animal
  • Have your dog defecate only on surfaces, such as cemented areas, that you can disinfect using tips shared on the CDC website. Areas with dirt (soil) and grass are impossible to disinfect effectively.
  • Limit your dog’s access to high-risk environments, such as kennels, dog day-care facilities, boarding facilities, dog parks, where giardia spread easily. Alternatively, seek places where pets get private spaces. Furthermore, do not board your dog until he is about a year old.
  • As much as possible, do not let your dog drink from outdoor water sources, such as communal water bowls (at pet-friendly places like parks, pet stores, and restaurants), puddles, ponds, rivers, lakes or streams, as they may be contaminated with feces from other animals. You’d have to provide access to safe, clean, cool water at all times, including during walks and outdoor activities.
  • Have your vet test your dog’s fecal sample for parasites at least once annually (twice in a year is ideal)