Causes, Symptoms, Diagnosis, and Treatment for Giardia in Dogs


"Contaminated water is one of the causes of giardia in dogs as well as general exposure in the environment such as exposure to contaminated surfaces in parks or even the dog's food if that also becomes contaminated. The disease (also called Giardia Canis and Giardiasis) is caused by protozoa that are encased in a protective cyst that cannot be seen by the naked eye. The dog then ingests these cysts, allowing one of three things to happen.

  1. Either the dog's immune system will eliminate the protozoan from the body, or
  2. The protozoa enter and multiply in the dog's small intestine, allowing them to reproduce causing cysts to be shed in the dog's feces
  3. which can then infect other dogs.

Most dogs show no symptoms (asymptomatic), but in those that do, symptoms develop in later states of the disease as the protozoa colonize in the intestines, feeding off the dog and preventing nutrients from being absorbed in to the body. Roughly 5% to 10% of dogs either have it (symptomatic) or have it but do not show any clinical signs (asymptomatic).  The incidence is 15% in clinically ill animals.

The protozoa blocks nutrients from being absorbed into the intestines, resulting in gastrointestinal problems such as continued or intermittent diarrhea along with weight loss. It is seen more often in puppies.The most common symptom of giardia in dogs is loose, but not watery diarrhea which is characterized by a foul odor and mucus. The dog diarrhea is often frequent and urgent. Other symptoms include gas, poor coat quality and vomiting. As the disease develops a dog will show weight loss and lethargy. Only a veterinarian can diagnose the problem.

Treatment involves the use of prescription medications that help to combat parasites. Adding fiber to the diet and supportive Herbal remedies can help speed recovery. If not treated ,a dog can remain infected indefinitely. The dog's home needs to be decontaminated with bleach.It is possible for giardia to be transmitted from dog to human, although this is uncommon, so use care when handling an infected pet. Dogs do not acquire immunity to giardia after treatment, so they can contract the disease again."

Dog Giardia Facts - Information Table
Dog Giardia Facts
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The most common causes of giardia in dogs is drinking from a lake, pond or stream that is contaminated with infected animal feces. The feces contains a cyst or small sac that enters the gastrointestinal tract of the dog.  The cysts protect or encase Trophozoites which actually cause the condition.

Protozoa causing Giardiasis in Dogs
Causes of Giardia in Dogs are protozoa passed in the form of a cyst that are ingested by dogs from feces in either contaminated water or when ingested from the environment such as a dog run or kennel.

The protozoa  divide in two rapidly and expand in number as they feed on and take away nutrients from your dog. The protozoa also produce harmful substances. Left untreated, Giardia can damage the lining of the small intestine and cause scaring.  Some of the Trophozoites will form new cysts, which pass out of or are shed from the body, allowing the disease to spread. Before they pass out of the dog’s body as mature organisms,they are encysted, as they travel to the large intestine. Unfortunately, these cysts are tough and can live outside their host for many months, so long as they are in the presence of moisture. Once these cysts are outside they contaminate the environment, e.g.; water and other food sources.

The disease is sometimes called Beaver Fever since beavers are known carriers of giardia. These are also the most commonly diagnosed protozoa in humans.

Coccidia is a similar parasite that affects the intestinal tract. Unlike the causes of giardia in dogs from lakes and streams, coccidiosis is contracted by eating feces directly.

Approximately 15% of dogs that have diarrhea and/or vomiting suffer from giardia.  In areas where there giardia is commonly found (such as areas with natural lakes and other waterways), approximately 6% to 11% of dogs shed giardia cysts.  Shedding of giardia cysts is more common in dogs under three years of age.

Video: Causes of Giardia in Dogs
Video overview of causes of giardia in dogs. Information on the giardia lifecycle.


Giardia in Dogs - Parasite Attaches to Intestines
Giardia in Dogs is Caused by a Parasite (Giardia Lamblia or Giardia duodenalis), which is found in streams and the soil. It enters the body through the mouth and then attaches to the dog's small and large intestines.
Photo Credit:

Giardia interferes with the absorption of nutrients from food. As can be expected, when you don't get the nutrients you need, you lose weight and appear to have less energy.

Dogs with Giardiasis may have no symptoms, as is the case in most dogs, or diarrhea and vomiting. In the majority of cases, blood is not found in the dog's feces. Diarrhea tends to be bad smelling and very watery. Diarrhea may be bad or light and occur frequently or far apart. Other symptoms include:

  • anorexia (appetite loss)
  • mucus in stool, light colored stools (blood in the stool is rare)
  • listlessness
  • lethargy (tired behavior)
  • dehydration
  • poor hair coat
  • flatulence

The incubation in animals is typically 5 to 14 days.


Giardia typically infects dogs that are less than a year old,but this is a general rule of thumb. This does not mean that an older dog may not get it or that an animal with another disease may not also contract it. You may also find Giardia in dogs enduring chemotherapy.

Your veterinarian will either study a stool sample or take a swap and wipe it at your dogs rectum. It is possible that the swap will not show any causes of giardia in dogs, yet your dog still has the disease. Your doctor will take 3 samples collected at least 2 days apart. There are also new blood tests that can detect the disease (called ELISA or IFA).

The veterinarian will also need to differentiate Giardia from other illnesses that have similar symptoms such as inflammatory bowel disease, pancreatic insufficiency, bacterial overgrowth and immunodeficiency.

If Giardia cysts are discovered during a routine examination of feces, it is up to the veterinarian and dog owner as to whether or not treatment is needed in dogs that are not showing any symptoms. Response to treatment can confirm the presence of Giardia, even if tests are negative.


The FDA has not approved any drugs for specific use against canine giardia. However, there are drugs commonly used by veterinarians which are highly effective in treating the infection as well as to stop the shedding of cysts in feces. The drugs Fenbendazole and Febantel are safe and effective in treating the disease and in eliminating shedding cysts. The drug metronidazole (trade name Flagyl)  is an alternative, but may have some side effects/toxicity, although positive include that it can be effective against other causes of diarrhea as well.

Albendazole is not routinely used until other medications are tried since it can have more side effects.

A complete list of dog giardia medications includes:

  • Metronidazole (Flagyl®,25-30 mg/kg, 7 days)
  • Fenbendazole (broad spectrum dewormer,  Panacur 50 mg/kg once daily, 3 days)
  • Furazolidone (Neftin, 4 mg/kg, 10 days)
  • Tinadazole (44 mg/kg once daily, 7 days)
  • Albendazole (Valbazen, 25 mg/kg, 2 days)

Immunotherapy with the canine giardia vaccine may help eliminate the shedding of cysts and diarrhea in dogs that already have the disease.

One approach for treating giardiasis is to use Panacur for up to 7 days (based on dog weight, check with your veterinarian/manufacturers directions). The medication is taken orally mixed with food. This is followed by a gap of 2 weeks, then another 7 days of treatment.  Panacur can be purchased on line from Amazon. Important: Only use an anti-parasitic medication such as Panacur if your dog has tested negative (does not have) heartworm. Dogs with heartworm can be harmed by using these types of medication as it will kill the worms and cause heart failure. To help protect your dog's digestive system during treatment, it is a good idea to use along with a probiotic supplement

In rare cases the use of fenbendazole can cause bone marrow toxicity, as bone marrow cells divide rapidly and are metabolically active. This can cause symptoms such as fever and via testing the presence of bone marrow hypoplasia/aplasia. Veterinarian's will check and rule out neoplasia (cancer) and check a urine culture before reaching this diagnosis (presumptive bone marrow hypoplasia/aplasia secondary to fenbendazole administration). Treatment for febendazole toxicity incoudes ampicillin (30 mg/kg IV every 8 hours) and enrofloxacin (5 mg/kg IV every 24 hours). Treated dogs will recover quickly with a return to normal temperature and appetite.

Supportive Treatment

  • Probiotocis: For dogs that are frequently diagnosed with giardia, one approach is to strengthen the condition of the gastrointestinal tract. Consider using a probiotic like Fortiflora.

  • Consider a change in diet to a higher fiber food. Adding fiber to your dogs diet can help protect against the causes of giardia in dogs and to help speed recovery. Fiber has the effect of helping to control symptoms such as bacterial overgrowth and makes it more difficult for the giardia protozoan to cling to the dogs intestines.

  • Several natural remedies can provide added GI support. These include Parasite Dr. to help the body naturally eliminate parasites, Natural Moves to restore bowel function and Digestive Support to improve nutrient absorption that was disrupted by the giardia.

  • You can also try a home remedy such as grapefruit seed extract diluted with water. Must be used faithfully for 14 days at 10-15 drops/10 lbs body weight at 3 times per day.

Giardia Vaccine in Dogs

To our knowledge the Giardia vaccine is no longer being made since it was generally considered to be ineffective.

Can Humans Catch Giardia from Dogs?

The causes of giardia in dogs are a different strain of parasite than the one that infects humans. Types of giardia are for the most part animal specific. The type found in humans, tend to stay in humans, dog giardia only infests dogs etc. In rare instances, human giardia has been found in dogs. While it is believed that it is possible for dog giardia to infect humans, there is no evidence that this is true, although more research is needed.

Cost of Care

Treatment for diarrhea costs under $100. Diagnosis for chronic cases costs between $100 and $500.


The only way to prevent giardia in dogs is to eliminate the causes of giardia in dogs which is standing water or unhygienic kennels or other areas where dogs congregate. When walking your dog, try and provide clean drinking water instead of relying on standing bodies of water or natural water sources such as lakes or streams.  There are no over the counter preventatives available like there are for parasites such as fleas.

Any place water collects should be removed if possible such as places where there are puddles or poor drainage. Any concrete surface should be cleaned, dried and sealed. Gravel areas should be replaced. Bleach may help clean infected areas (1% bleach, 99% water). Lysol, ammonia, and bleach can also be effective decontamination agents. Look for products that contain quaternary ammonium compounds.

Removal of Giardia is difficult. They survive the chlorination of drinking water and freezing down to –13C.  Cysts can last in the environment for several weeks. They can last even longer if in the water.

To avoid causes of giardia in dogs such as feces, practice good hygiene such as bagging and disposing of feces in bags, and removing and disposing deposited in outdoor areas such as the backyard.

For more information on the causes of giardia in dogs, download this free pamphlet from the Companion Animal Parasite Council on Giardia in dogs and people.


Free brochures on the treatment and causes of giardia in dogs.

Update on the diagnosis and management of giardia in dogs.
Available in a free Ebook

Fact sheet that outlines the dog giardia basics.
Available in a free Ebook

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Department of Clinical Sciences
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