Dog Parasites - Giardia, Giardiasis


also see Canine Valley Fever


Giardia is a protozoan parasite that lives in the intestine of affected animals. It is unclear whether there are several species of this parasite or whether there is one species that affect several different animals, including people. These small parasites are very easy to miss on a fecal exam and may not be present in the stool of animals infected with the organism. Repeated fecal exams are sometimes necessary to identify this parasite. Not all animals in which infection can be demonstrated have clinical signs. This leads some people to believe that the parasite may not cause disease . Most vets think that there may just be other factors, like the animal's immune response to the parasite that cause some animals to develop disease and not others. Clinical signs of giardia include weight loss, inability to gain weight appropriately during growth, diarrhea, vomiting, lack of appetite and greasy appearing stools. Them most commonly used medication for giardia infection is metronidazole (Flagyl). The organisms come from the environment and live in moist to wet areas. They are susceptible to quatenary ammonium disinfectants, Lysol and dilute chlorine bleach. Keeping the dog's environment dry helps a lot.

This disease may be contagious to people from infected dogs so good sanitary practices, like washing your hands after handling an infected puppy, are very important. If a family member develops similar clinical signs, a physician should be consulted.

Mike Richards, DVM

Beaver Fever or giardiasis

Question: Dr. Richards,

Please tell me ALL you can about "Beaver Fever," in dogs.

1. What are the symptoms at initial onset? 2. What is the prognosis and, does it differ depending on the age or breed of the dog? 3. Is this term interchangable with "Valley Fever"? (or a disorder completely different). 4. Can it be transmitted to humans and, if so, how? 5. Is it contagious to other pets, i.e., dogs. 6. HOW is it diagnosed? 7. What are the preferred methods of treatment? 8. What are treatment OPTIONS? 10. Which part of the country is this most prevelant? 11. Is isolation of the infected dog necessary and, if so, for how long? 12. Does it (typically) recurr once cured? 13. IS it "curable?" 14. Where does it gets it's name? Does contact with (only) a Beaver cause this? 15. Is it viral, bacterial, fungal, etc.?

Anything you can add would be appreciated.

Thanks, Vox

Answer: Vox-

There is a chance that "beaver fever" is used as a name for more than one condition but the only one I am familiar with is giardiasis, an infection with the organism Giardia lamblia. The Giardia organisms can infect a number of species. Humans who drink water in which beavers have "done their business" sometimes become infected with this organism, which produces flu like symptoms in humans, sometimes including diarrhea and vomiting and less commonly resulting in death. Beavers are not the only animal that can pass this infection on to humans. Infected dogs and cats have to be considered as potentially capable of infecting humans.

In dogs, giardiasis is most commonly an inapparent infection. There are all kinds of estimates of the number of dogs infected with this parasite, ranging from a a small percentage up to 70%. The infection rate probably varies really widely by region, resulting in the variations in reported infection rates. In any case, since the organism can be found in a lot of dogs with no apparent symptoms it is safe to assume that most dogs do not have clinically apparent disease when they have giardia.

Young puppies, young kittens, immune compromised patients and dogs with multiple parasite infections are more likely to actually have clinical signs associated with giardiasis.

Giardia can be very hard to find through fecal examinations so it is hard to be sure that it isn't present when clinical signs of diarrhea, poor weight gain or unthriftiness are present. It is best to run several fecal examinations when this infection is suspected but does not show up in the initial stool sample(s) run.

Treatment options include metronidazole ( 25 to 30mg/kg for at least 5 days), fenbendazole (Pancur Rx) at 50mg/kg for 3 days, albendazole and furazolidone. So far, we have not tried the last two options in our clinic because one or the other of the first two has worked to eradicate the giardiasis.

Giardiasis occurs almost everywhere there is water (the most common way for it to be transmitted, but direct contact also occurs). I think that it is probably most common around the Great Lakes, but that is only my impression based on watching postings on the veterinary message boards on the Veterinary Information Network (VIN) and noticing a lot of them on this condition from Wisconsin and that general region.

I think that some dogs and cats get this condition several times in their lifetime. There is a vaccine that helps to prevent the symptoms from occurring in dogs that are very susceptible and in puppies that are likely to be exposed.

I hope that this helps some.

Mike Richards, DVM 1/18/2001

Zoonotic aspects of Giardia

Q: If a person has had contact with a giardia-infected dog but was unaware of the bacteria's presence and didn't practice good sanitation, what can be done? Please respond, someone very close to me has infected dogs and many people have played with them unwittingly (though none have shown signs of it, based on the symptoms I was taught in Boundary Waters MN), and we do not want to be infected. What are the signs in people, and can you refer me to good informative sites about this? Thank you, Erik

A: Erik-

There is still controversy over whether or not giardiasis is a zoonotic disease -- a disease that can be passed from pets to humans. According to Drs. Leib and Zajac, writing in Kirk's Current Therapy XII, the dog and human strains of giardia have different characteristics while the cat and human strains are more similar. However, until there is definite proof one way or the other it is a good idea to consider contact with fecal material from infected dogs to be potentially infective to humans.

As you point out, good sanitation, such as hand washing after playing with the dogs and avoiding contact with the dog's feces is the best defense against this condition. Giardia species are water-borne protozoans and contaminated water sources are probably the most likely source of infection for both pets and people.

Metronidazole and fenbendazole are reasonably effective at eliminating Giardia organisms from infected pets so treatment of the dogs would be a good idea. Metronidazole is inexpensive so financial concerns shouldn't prohibit treatment in most cases.

I am not sure if people have the same signs as dogs but the giardiasis in dogs is often asymptomatic (i.e. the dogs are not sick at all) but it may cause diarrhea.

You can probably find a lot of information on giardia at the PubMed site. We have a link to it from our link page.

Mike Richards, DVM


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...