Giardia is a type of protozoan parasite that can affect a number of animals, including dogs and humans. Because it can be spread from animals to humans, it is considered a zoonotic disease. The disease caused by Giardia infection is called giardiasis, and its most common symptom in dogs is diarrhea.
What Is Giardia?
Giardia is not a worm, but a microscopic, single-celled parasite. There are numerous species of Giardia, and not all have been identified. However, it is known that Giardia can exist in two forms--trophozoites and cysts. Trophozoites are the active form and have long whip-like appendages called flagella, which enable them to swim throughout the intestines of a host. In the intestines, the trophozoites attach to and damage cells in the small intestine, which leads to maldigestion, malabsorption, and diarrhea. Trophozoites can also form cysts that are designed to survive outside a host's body.
How Dogs Get Giardia Infections
Giardia is shed in the stool of infected animals. Giardia cysts can survive in the environment for days to months depending on conditions. The cysts thrive in cold water, living for one to three months. Viability decreases as water warms. They can survive in cooler soil temperatures for up to 7 weeks and for about a week in warmer soil or on surfaces.
Infection occurs when Giardia cysts are ingested. Dogs and puppies contract Giardia by drinking contaminated water, eating off the ground where contaminated soil is present, or self-grooming after coming into contact with contaminated soil, stool, water, or another contaminated material. Humans are most commonly infected with Giardia after coming in contact with the feces of a person shedding Giardia or drinking contaminated water. Fortunately, evidence shows that dog-to-human transmission of Giardia is rare.
Signs of Giardia in Dogs
Many dogs with Giardia have no symptoms, but if they do, the most common sign is diarrhea, which may be pale and foul-smelling. Flatulence may also occur. Some 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 specifically for Giardia if your dog is sick. However, routine wellness parasite screening may reveal the presence of Giardia. Giardiasis is not as simple to diagnose as some other common intestinal parasites because it is not consistently shed in the stool (due to the organism's life cycle). There are a few ways Giardia can be detected by a veterinarian.
- 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 a small stool sample and a test kit; no microscopic examination is needed. Most veterinarians can perform this test in-house for fast results.
A combination of tests, often performed using fecal samples collected on different days, may be needed before giardiasis can diagnosed.
Giardia Treatment for Dogs
There are a few ways Giardia infection can be treated in dogs. Although not approved by the FDA, metronidazole is one of the most commonly used drugs to treat giardiasis in dogs. Your vet may prescribe a dewormer called fenbendazole (Panacur) to be administered orally for 3-7 days.
Though less commonly used, some vets may prescribe a broad-spectrum dewormer called Drontal Plus (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 help prevent other animals (including humans) from contracting Giardia and your dog from becoming reinfected.
- Feces should be removed from your yard immediately to minimize the chances of contamination. Scoop the yard at least one to two times daily. Eliminate any standing water in the yard if possible. Unfortunately, it is difficult to fully decontaminate the yard, but keeping it clean minimizes the risk.
- Affected dogs should be bathed when diagnosed and again after treatment is completed to remove feces and cysts from their fur.
- 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.
- Be sure to comply with your veterinarian's recommendations regarding follow-up.
Disorders Caused by Protozoa in the Digestive System of Dogs. Merck Veterinary Manual, 2020
Overview of Giardiasis. Merck Veterinary Manual, 2020
Moron-Soto, Mario et al. Efficacy of nitazoxanide to treat natural Giardia infections in dogs. Parasites & vectors vol. 10,1 52. 31 Jan. 2017, doi:10.1186/s13071-017-1998-7