Overview 

Giardia is a common, tiny, intestinal parasite that can cause diarrhea in dogs. Common in the environment, Giardia, can be found in feces-contaminated soil, food and water.  

While some dogs infected with Giardia may not show any signs of infection, younger dogs and dogs with weakened immune systems are more likely to display clinical signs. Dogs can easily reinfect themselves with Giardia, so successful treatment relies on effective anti-parasitic medications, cleaning and managing the surrounding environment. 

Causes 

Dogs get Giardia from ingesting feces-contaminated water, soil, food or objects. 

Giardia has two forms: trophozoites and cysts. Trophozoites live in the intestines of infected dogs. Cysts are trophozoites with a protective covering. Infected dogs pass, or shed these tiny, cysts in their feces. 

Cysts are hardy and can survive in the environment for months. They are instantly infectious, and just a few ingested cysts can cause infection. Dogs can easily reinfect themselves by licking or grooming themselves if cysts remain on their fur, paw pads or rear end. 

Clinical signs 

Many dogs have no clinical signs and still have a normal appetite and energy levels. When clinical signs do appear, the most common are: 

• Diarrhea, which may be sudden, or chronic on-and-off
• Soft or watery stool with mucus and a foul odor 
• Abdominal discomfort  

In severe cases, dogs may experience lethargy, decreased appetite or weight loss.  

Diagnosis 

Your veterinarian will test a fecal sample from your dog. Because Giardia cysts can be shed intermittently in the feces, they might not be seen on a single sample. Testing consecutive fecal samples daily for three days is helpful to confirm infection.   

An additional test looking for Giardia-specific antigens, which are small proteins made by the parasite may also be performed. This test is not affected by the intermittent shedding of cysts so testing for it once is effective. 

Some labs also offer PCR testing, which is a DNA-based test that can identify the specific type of Giardia present and help determine whether the infection poses a risk to the pet owner.

Treatment 

The goal of treatment is to resolve diarrhea and other clinical signs. Dogs without clinical signs may not require treatment unless they share a home with puppies, animals with weakened immune systems, or people at risk of infection and the dog is known to carry a Giardia type that can spread to humans.

• Medication 

  • Fenbendazole is a common deworming medication used to treat Giardia.  
  • Another treatment option is an antibiotic called metronidazole.  
  • Other medications may be used if the infection does not respond.

• Diet 

  • Your veterinarian may recommend a diet that supports digestive health to help resolve diarrhea, such as one with high fiber. 

• Bathing 

  • Dogs should be fully bathed on the last day of treatment to remove fecal material and any remaining Giardia cysts in the dog’s fur. 

• Cleaning  

  • Common household disinfectants and steam-cleaning are the most effective ways for killing Giardia cysts.  
  • Remove and dispose of all feces promptly. 
  • Giardia cysts on the lawn can only be killed by direct sunlight drying them. 

Outcome 

Most dogs fully recover with proper treatment.  

If diarrhea continues after treatment, your veterinarian may recommend rechecking a fecal sample to see whether your dog has been reinfected. Retesting for antigens is not recommended because Giardia antigens can remain present days after treatment even after the parasite is gone.    

Dogs may become reinfected if their surrounding environment is not properly managed. Additionally, if the Giardia is resistant to the medication used or if the medication was not dosed properly, then refractory infections may also occur.   

Zoonosis 

The risk to people is low. While humans and other species can become infected with Giardia, the Giardia types found in dogs are different from those that usually infect people. There are some types that can infect both dogs and people, though this is less common. For this reason, it is uncommon for humans to get infected from a strain of Giardia that pets may carry and vice versa. Thorough hand washing with soap and water after handling pets or their feces is always important.

Contagion to other pets

An infected dog is generally a low risk to a healthy cat because dogs and cats are mostly affected by different types of Giardia. There are some types that can be shared, so passing it to each other is not impossible. The same is true in reverse.  

Other dogs in the home may be at a higher risk of exposure. You can limit the risk by having the dogs defecate in separate areas, wiping the infected dog’s rear end after defecating and preventing them from grooming each other. Continue to dispose of feces promptly, bathe the infected dog at the end of treatment and wash your hands after petting your dog or handling their feces.