Giardia in dogs (also known as giardiasis) became well known several decades ago when a different strain of the organism was identified as causing persistent diarrhea in people. Once an understanding was developed that the condition is spread through feces contaminated swimming pools, food, drinking water, and surfaces, did the awareness of the disease increase. This awareness led to an understanding of giardiasis in animal health and improvements in detection methods.
Causes of Giardia in Dogs (Left and Rights: Giardia Protozoa; Center: Cyst)
Source: CDC
Causes of Giardia in Dogs (Left and right: Giardia Protozoa ; Center: Cyst) Source: CDC
Studies show that approximately 4% to 6.8% of dogs shed giardia cysts. The cysts are shed by infected dogs from the small intestines and are passed through the feces. Rates of infection are higher in younger dogs with 12% of dogs under age 6 months testing positive for the disease. This rate is significantly lower in dogs 3 and older, where only 1%$ shed cysts.
The protozoa that causes giardia in dogs are transported in protective cysts which protect the protozoa until they reach the next host. Giardia can last in the environment for several months.
How Giardiasis is Spread from Dog to Dog
The infection spreads when a dog ingests cysts found in feces after ingesting contaminated water, food, or from fomites in the environment such as a park, improperly cleaned kennel or dog run. Once the cysts are ingested, the giardia protozoa begin to multiply and attach to the dog’s small intestine. As they feed off the dog, they rob the dog of nutrients through mal-absorption and problems with the digestive system through mal-digestion (incomplete digestion). Protozoa that feed on a host are referred to as trophozoites. Any surface that is contaminated, including food, play toys etc that came in contact with feces from a dog that is shedding giardia cysts, can be one of the causes of giardia in dogs.
A dog will start shedding cysts in 5 to 7 days after being infected.
Each Person, Dog or Cat is infected with a different strain of Giardia
The giardia that infects dogs (giardia canis) is different than the giardia that infects cats (giardia felis) or the strain seen in humans.  In general, dogs in the Northeastern United States have a higher incidence of the disease over the Southeastern United States (DD Bowman 2011, Carlin 2006).
Dog Giardia Symptoms
The most common giardia dog symptoms are moderate to severe diarrhea with or without mucus. It is rare for the diarrhea to contain blood. Other symptoms includes vomiting. Most dogs that shed giardia cysts are asymptomatic, which means that they do not show any giardia symptoms.
Diagnosis of Dog Giardia
Giardia diiagnosis in dogs is accomplished in the veterinarian’s office with one of several types of tests. This includes a centrifugal fecal flotation test or fecal ELISA test. Note that the majority of dogs are asymptomatic or symptom free. In this case, giardia in dogs is detected as part of tests conducted during a checkup, called fecal centrifugation. If this is the case, your veterinarian will discuss with you the pro’s and cons of treating a dog that does not show symptoms.
Canine Giardia Treatment
There are several prescription medications available for giardia dog treatment. This includes:
- Fenbendazole/febantel (50 mg/kg for 5 days) is effective in most dogs.
- Metronidazole (25 mg/kg 5 days). In some dogs Metronidazole can be toxic (Per 2010 CAPC Guidelines).
- Drontal Plus (3 days)
Homeopathic supplements can help to restore digestive health after prescription treatment. Recommended supplements include Parasite Dr. to restore the body’s natural defenses against parasites and a fiber rich supplement such as Natural Moves to help restore digestive health.
If a dog becomes severely dehydrated from the diarrhea, fluid therapy in the veterinarian’s office will be necessary.
Dog Giarda Vaccine
The dog giardia vaccine is not considered a core or mandatory vaccine. Exposure of a dog to potential sources of giardia such as other dogs and contaminated waterways should be considered as part of the decision to vaccinate.
Can Humans Catch Giardia from Dogs (Zoonotic)?
The strain of giardia found in humans has been found as the source of infection in a limited number of dog giardia cases. For this reason, there is some risk that giardia can pass from human to dog. If a dog is infected with a human strain it could theoretically pass back to humans, although this is considered to be rare. Because of this, proper hygiene should be followed when handling an infected dog. Always be careful when disposing of feces.
Giardia Dog Prevention
Only give your dog fresh drinking water when outdoors. Avoid allowing your dog to drink from any standing water that could be contaminated. If your dog defecates outdoors, such as in a backyard, clean-up all feces. Dogs that have been positively diagnosed should have a bath to remove any cysts that could be hiding in the coat.
These hygienic steps are necessary to prevent reinfection, as it is common for this to occur in giardia in dogs cases.
References
Giardia in Dogs, Dog Health Guide
Update on Giardia and Cryptosporidium in Dogs and Cats
D.D. Bowman
College of Veterinary Medicine, Cornell University, Ithaca, NY, USA.
Companion Animal Parasite Council Guidelines, Giardia
Giardiasis in Dogs and Cats: Diagnosis, Treatment, and Zoonotic Risk
Susan E. Little, DVM, PhD, Dipl. EVPC
Center for Veterinary Health Sciences
Oklahoma State University, Stillwater, OK, USA
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