How Giardia Can Affect Dogs

Giardiasis Infection and Your Dog

Illustration of Giardia trophozoite. © Eraxion/

Giardia is a type of protozoan parasite that can affect a number of animals, including dogs and humans (it is considered a zoonotic disease). Giardia infection is called giardiasis and most commonly causes diarrhea in dogs.

What is Giardia?

Giardia is not a worm, but a microscopic single-celled parasite. There are numerous species of Giardia, and not all are known. We do know that these organisms live in the intestines of animals in the form of trophozoites.

The trophozoites have long whip-like appendages called flagellates, which enable them to swim throughout the intestines. In the intestines, the trophozoites attach to enterocytes in the small intestine, leading to maldigestion, malabsorption, and diarrhea. Outside the body, two trophozoites join to create a protective cyst. This allows them to survive in the environment to affect a new host.

How Does Giardiasis Occur?

Giardia is shed in the stool of affected animals. Giardia cysts can survive in the environment for weeks to months, depending on conditions. The cysts thrive in water (living 1-3 months) and cooler soil temperatures (up to 7 weeks), but they can still survive for about a week in warmer soil or on surfaces. Giardiasis occurs when Giardia cysts are ingested. Dogs may drink contaminated water, eat off the ground where contaminated soil is present, or self-groom after coming into contact with contaminated soil or stool (or another contaminated surface).

Humans are most commonly infected with Giardia after drinking contaminated water. Fortunately, evidence shows that dog-to-human infection is rare.

Signs of Giardia in Dogs

The most common sign of giardiasis is diarrhea. Often, this diarrhea becomes bloody. Bloating and flatulence may also occur. Many dogs display general malaise, lethargy, and loss of appetite.

Though less common, vomiting sometimes occurs with giardiasis. If left untreated, giardiasis can lead to weight loss, malnourishment, dehydration and more. If you notice these signs (or any other signs of illness) in your dog, contact your veterinarian.

Diagnosing Giardia in Dogs

Your veterinarian will usually only test for Giardia if your dog is sick, although routine testing may reveal the presence of giardiasis. Giardia can be difficult to diagnose, as it is not consistently shed in the stool due to the organism's life cycle. There are a few ways Giardia can be detected:

  • Direct fecal smear: fresh stool is mixed with saline and examined microscopically.
  • Fecal flotation with centrifugation: stool is mixed with a special salt/sugar solution and centrifuged (spun in a special machine at high speed). The sample is then microscopically examined.
  • Giardia ELISA test: a specialized test that detects antigens in feces. This test uses small stool sample and a test kit; no microscopic examination is needed. The Giardia ELISA is considered the most effective for diagnosing dogs with giardiasis.

Giardia Treatment for Dogs

There are a few ways giardiasis can be treated in dogs. Your vet may prescribe a dewormer called fenbendazole (Panacur) to be administered orally for 3-7 days.

An antibiotic called metronidazole (Flagyl) may be prescribed concurrently or separately. However, evidence shows that use of metronidazole alone is less effective. In addition, metronidazole in high doses can adversely affect some dogs.

Though less commonly used, some vets may prescribe a broad-spectrum dewormer called DrontalPlus (combination of febantel, pyrantel pamoate, and praziquantel) to be administered daily for 3 days. However, this may be cost-prohibitive. Talk to your vet about the best drug options for your dog.

Giardia Prevention and Control

Regardless of the medical treatment used, it is important that you do your best to eliminate Giardia from your dog's environment. This will prevent humans and other dogs from contracting Giardia and prevent your dog from re-infection.

  • Affected dogs should be bathed when diagnosed (and ideally again after treatment is completed).
  • Bedding should be washed frequently during treatment and again when treatment is complete.
  • Surfaces can be cleaned using bleach and water at a 1:32 dilution ratio. Or, steam-cleaning can be performed and areas allowed to dry.
  • Feces should be removed from your yard immediately to minimize the chances of contamination. Scoop the yard at least 1-2 times daily. Eliminate standing water in the yard if possible. Unfortunately, it is difficult to fully decontaminate the yard, but keeping it clean minimizes the risk. Some sources suggest steam cleaning as an option outdoors.
  • Have your dog's stool rechecked after treatment! Be sure to comply with your veterinarian's recommendations regarding follow-up.