Giardiasis or the condition commonly known as Giardia in dogs 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 right: Giardia Protozoa ; Center: Cyst) Source: CDC
Studies show that approximately 4% to 11% of dogs shed giardia cysts although by 3 years of age this percentage drops to 1% (2). 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.
The incubation period is 5 to 14 days.
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). That said interspecies transmission of the parasite has been demonstrated, such as transmission from human to dog, although this is still disputed in the medical community. (1)
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. Clinical symptoms appear in approximately 15% to 16% of dogs that have been infected by the parasite.
Diagnosis of Dog Giardia
Giardia diagnosis in dogs is accomplished in the veterinarian’s office with one of several types of tests. This includes a direct smear test (used to test diarrheaic stools), a centrifugal fecal flotation (if the stool is completely or mostly solid), fluorescent antibody assay or a fecal ELISA test (called SNAP® Giardia). 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.
It is recommended that Vets use a combination of tests in dogs that have symptoms. It might be necessary to perform tests on different days.
Canine Giardia Treatment
There are several prescription medications used by veterinarians for giardia dog treatment.
- Fenbendazole/febantel (50 mg/kg for 5 days) is effective in most dogs (considered to be more effective than Metronidazole)
- Metronidazole (25 mg/kg 5 days). In some dogs Metronidazole can be toxic (Per 2010 CAPC Guidelines).
- Drontal Plus (3 days)
Note that none of these medications is approved to specifically treat giardia, however fenbendazole is approved in Europe. If a single or the use of multiple of the above medications does not work in the first 5 days, treatment is extended for 10 days. Dogs that live with an infected dog are often treated using a 5 day course of treatment.
Homeopathic supplements are thought by some owners to restore digestive health after prescription treatment. Supplements that we suggest discussing with your Veterinarian 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.
Always wear gloves when handling any contaminated items. All surfaces should be disinfected in the home including crates, tile floors, and cement. Use either bleach (3/4 cup of bleach to 1 gallon of water) or cleaning products that list alkyl dimethyl ammonium chloride or quaternary ammonium compound products (QATS). Follow the manufacturers instructions.
Carpets should be cleaned with paper towels and disinfected using a steam cleaner (steam at 158F degrees for 5 minutes or 212F for 1 minute) or with a product that contains quaternary ammonium compound (QATS).
Clean and disinfect all dog toys daily. Pet clothes can be cleaned (bedding, cloth toys etc.) in a washing machine followed by drying in a dryer on the high heat setting for 30 minutes. As an alternative, air dry in the sun.
Dog Giarda Vaccine
The dog giardia vaccine is not considered to be effective and is now off the market. When the vaccine was available, dogs where not treated via vaccination.
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. To be clear, this is a rare occurrence. 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. The parasite can only be passed through feces that is swallowed, it cannot be passed through blood.
If swimming pool water has been contaminated with feces from an infected pet, it can pass to another healthy pet. Giardia can stay alive for 45 minutes in pools that are properly chlorinated. Symptoms of human giardia are diarrhea for 1 to 2 weeks.
Giardia in the Environment
Giardia can survive in the cold to around 4 degrees Celsius or 39.2 degrees Fahrenheit. At room temperature, giardia will survive for approximately 7 days. In the water, giardia can survive for 1 to 3 months at temperatures below 10C or 50F. Above this level the parasite can survive less than 4 days.
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.
(1) Ohio State University
(2) Oklahoma State University, Susan E. Little DVM, Giardiasis in Dogs and Cats: Diagnosis, Treatment and Zoonotic Risk
Giardia in Dogs, Dog Health Guide
Update on Giardia and Cryptosporidium in Dogs and Cats
College of Veterinary Medicine, Cornell University, Ithaca, NY, USA.
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
Page Updated and Reviewed: 10/18/14