Giardia in Dogs: Understanding This Infection and Treatment

Published November 17, 2021
English Springer Spaniel

Anytime your dog develops diarrhea, it's understandable to search for potential causes. Consider putting giardiasis on the list. All dog owners should understand the dangers of Giardia in dogs and how to address this microscopic parasite.

What is Giardia in Dogs?

Giardia is a protozoan parasite that affects a dog's intestinal tract, often leading to severe, watery diarrhea. Dogs contract this parasite through infected animal feces. This can occur from direct ingestion of stool or through contact with contaminated surfaces like standing water, soil, or grass. The disease caused by Giardia is called giardiasis.

Giardia has two life stages: cyst and trophozoite. The cyst is the inactive stage that is shed in stool. Once ingested, cysts develop into trophozoites. Giardia trophozoites are the mobile, active form of the parasite that reside in the intestines and absorb the host's nutrients. They produce cysts which are shed in the feces and continue the life cycle.

Unfortunately, Giardia cysts can survive in the environment for up to several months, even in subpar conditions. This means if your dog happens to lick their paws after walking on an area that contains feces from an infected dog, they could ingest the cysts and contract Giardia.

Giardia is a protozoan parasite

Signs and Symptoms

Because giardiasis interferes with nutrient absorption within the intestines, this parasite most commonly causes diarrhea. This diarrhea can come or go or may be persistent, and it often contains mucus. Some of the most common clinical signs include the following.

  • Watery diarrhea
  • Diarrhea with mucus
  • Bloody diarrhea
  • Flatulence
  • Foul-smelling stool
  • Soft stool
  • Urgency to defecate
  • Weight loss
  • Lethargy
  • Decreased appetite
  • Vomiting

It's important for pet owners to know that a dog can be infected with Giardia without showing any signs. This is troublesome because an asymptomatic dog can still shed the parasite into the environment and infect others. Proper stool clean-up and hygiene are important to protect yourself and other pets.

Potential for Giardia Transmission

When a dog is actively shedding Giardia cysts, the parasite is highly contagious to other dogs. Dogs are notorious for sniffing or tasting anything that they encounter, so the chances of a housemate, playmate, or even a passerby dog contracting the disease from an infected canine are very high. Reinfection of the same pet is also possible due to the resilience of the cysts.

On the other hand, the chances of a human contracting Giardia from a dog are quite low, but not impossible. Giardia has several variants, and the canine strain is unlikely to infect humans. However, immunocompromised individuals should be particularly cautious, and it's wise for everyone to wash thoroughly after playing with a dog or picking up their feces.

Obtaining a Diagnosis

Using a microscope

There are several diagnostic methods veterinary hospitals use to test for Giardia. Each requires a fresh stool sample.

  • Fecal flotation. For this method, feces is mixed with a special solution then placed in a centrifuge. The carefully timed procedure is designed to bring any Giardia cysts to the surface of the solution, where they are collected then examined under a microscope.
  • Fecal cytology. A different method is used to look for Giardia trophozoites. The veterinary team can identify the mobile Giardia by placing a sample of stool directly onto a slide (with or without a special stain).
  • SNAP test. An in-hospital antigen test can give you a positive or negative result pointing to giardiasis in a matter of minutes. This test requires a small amount of feces and detects the presence of the parasite's antigens. It's best used in conjunction with one of the manual identification methods.
  • Reference laboratory testing. Your vet may recommend sending the stool sample to a reference lab for further testing, where they may perform an immunofluorescence assay or PCR tests. It can take several days for these results.

Obtaining a giardiasis diagnosis can be challenging in some cases due to the parasite's intermittent shedding. Don't be alarmed if your vet recommends repeated testing over several days.

Treatment Options for Giardiasis

Veterinarian giving medication to dog owner

Canine diarrhea can have various causes, so it's important to see your vet if you suspect that your pet may have giardiasis. Based on your pet's exam and diagnostic results, they can make appropriate recommendations.

Most treatment plans consist of a course of Metronidazole (also known as Flagyl) for several days and a broad-spectrum prescription dewormer. Supportive care to address dehydration from persistent diarrhea or medication for nausea may be necessary, as well. Although some natural sources like pumpkin seeds may have anti-parasitic properties, no holistic remedies have been proven to treat giardiasis.

Preventing Giardia

Woman cleaning

You can help reduce your dog's risk of becoming infected with Giardia through these measures.

  • Promptly remove dog feces from your yard.
  • Clean up after your dog while in public areas.
  • Do not allow your dog to eat feces.
  • Provide clean, fresh water for your dog.
  • Keep your dog from drinking standing water.
  • Remove any standing water from your yard.

If your dog has giardiasis or is being treated for a Giardia infection, keep them away from public areas until after treatment when they are no longer shedding the cysts. This will protect other dogs from picking up the parasite.

It's possible that a dog can become reinfected with Giardia from their own stool. Thoroughly clean your environment and disinfect any items that could have been contaminated to prevent this from happening. A diluted bleach solution (1:32 or 1:16 part solution) can effectively kill the Giardia cysts.

Early Treatment is Key

The best way to address giardiasis in dogs is by catching it early. See your veterinarian or drop off a stool sample at the earliest onset of diarrhea to ensure your pet's comfort and prevent spreading the parasite. And don't forget to wash your hands!

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Giardia in Dogs: Understanding This Infection and Treatment