Giardia and Suggestions for Treatment

Giardia is a single-cell organism in what we used to call “the animal kingdom” because early classification systems distinguished animals from plants by the ability of the former to move from place to place “of their own free will.” The Giardia cell does this by whipping its appendages, like a shark’s tail, or a sperm cell. This flagellant action propels it through much of the dog’s (or human’s) digestive system.

Bacteria, on the other hand, were considered the simplest, most basic members of “the plant kingdom” because they were not so motile. That distinction had lost significance with the discovery of intermediate forms of tiny life, such as hard-to-classify viruses and others. Further complicating attempts to categorize organisms is the fact that many exist in a non-motile stage for a while, and are capable of “travel” during other times. Enough reason to call many of them simply “organisms.”

By themselves—but much more when aided by other pathogenic allies—these microscopic “animals” can cause diarrhea and sometimes, in the case of the very young or very old, death. Like several other disease organisms that go through a resistant spore or egg stage, they have defenses against eradication. In these stages, they can be picked up again by the same animal that excreted them, or by another host. It is not uncommon for humans to become infected. Giardia and so many other parasites must be fought on the battlefield of the outside environment as well as inside their victims.

Adult dogs that are in otherwise good health and have few or no other parasites often develop a resistance to Giardia, although they should be treated for it anyway, if stool checks of any dogs in the family show the presence of cysts. Or even if symptoms point to Giardiasis without microscopic confirmation. Younger animals have a higher rate of infection and are more seriously affected. If very young puppies also have hookworm or another concurrent problem, the combination can be fatal, or can weaken the animal so that it succumbs to some other newly-encountered challenge.

Giardia is extremely hard to get rid of in the soil. Part of the reason is that this protozoan parasite forms oocysts, which are like eggs but with a covering or shell that is very resistant to harsh environments. These oocysts can persist in the soil and in cracks in floors for many months, perhaps even years, especially in cool and moist areas. If possible, immediately scoop all feces with the grass and soil underneath, and bury deep. Wash the shovel or scoop with bleach, away from where dogs will later walk. I used to employ a “flame-thrower” which was a cylinder with a pump and a nozzle, from which pressurized kerosene was mixed with air and the flame from the torch was applied to the spots on the soil or concrete runs where the feces had been.

Giardia cysts in a kennel with floors (especially those without cracks or crevices) are relatively easy to destroy with routine disinfectants, and are susceptible to drying and heat. In the house or kennel building or dog-run, clean the floors and equipment such as mops, boots, etc. with a slightly diluted bleach solution—I recommend 50/50. Or you could use a quaternary ammonium disinfectants (get it from your vet or his supplier), or Lysol. Keeping the dog’s environment dry also helps a lot.

Giardia is acquired by ingesting cysts from contaminated water, whether streams or standing; contaminated food from the street, or via coprophagia. Cysts can sometimes be found on the fur or paws, collected by walking or rolling on the ground, and are then ingested when the dog grooms itself. Giardia may occur in people as well, in fact, Giardia is the most common intestinal parasite affecting people in North America. Many war veterans returning from Southeast Asia in the 1970s had these stowaways in their digestive tracts. My mother once thought she was dying of cancer because of uncontrollable, recurring-persistent diarrhea and other symptoms. After exhausting all other tests, one day some doc had a bright idea and did a higher-magnification stool check and found the oocysts! Treated for this parasite, she immediately regained health.

Once an environment like a lawn is contaminated, though, and especially if you don’t pick up the stools and disinfect the spot right away, it can be almost impossible to eliminate this parasite. Good nutrition, avoiding overcrowding, general parasite control, and proper sanitation procedures are all helpful in elimination of Giardia and prevention of recurrence. Cleaning up feces on an immediate or twice-daily schedule goes a long way to preventing re-contamination. The organisms can persist in moist to wet areas, so keeping the dog’s environment dry helps.

The Giardia parasites are small, and “eggs” are very easy to miss on a fecal exam; they may not be present in every stool sample from animals infected with the organism. Repeated fecal exams and/or multiple stool samples are sometimes necessary to find and 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 (to be asymptomatic), 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.

A friend in Uruguay told me that his vet prescribed “500 mg Albendazol + 50 mg praziquantel every 12 hours for 3 days” to rid his dogs of the protozoa parasite Giardia lamblia, but he had tried this repeatedly and unsuccessfully for months. I told him I didn’t think the praziquantel by itself is especially effective against Giardia—it’s possibly given in order to kill or control other parasites such as worms, because a “wormy” dog will have much less ability to fight off Giardia. It does seem to help, though, when combined with febantel and pyrantel pamoate. (Nemex and Strongid are well-known brand names for pyrantel.) More on febantel and fenbendazole further down.

Metronidazole (the most popular brand name is Flagyl, so named because the protozoan organism it targets is a flagellate, having a whip-like tail) is routinely used to treat Giardia, although it does not cure all those infections and is not all that good to give to pregnant bitches. The usual course of therapy is for 5 days at a time, although veterinarians may vary this dose depending on specific circumstances and personal preference; other medications are used if the Flagyl is not effective. One veterinary website says, “There is no drug that is 100% effective against Giardia.” Some say it is generally less effective than fenbendazole and that some studies suggest that Giardia is more likely to form resistance to this medication. However, I had great success with Flagyl, many years ago. I have seen it to be effective in both dogs and humans. Today, I would first try Drontal-Plus, keeping Flagyl on hand as a back-up.

Treatments for Giardiasis in dogs

Drug Name

Trade Name

Dose Rate

Duration of each Treatment


Flagyl **

25-30 mg/kg bid

7 days


Neftin *

4 mg/kg bid

10 days


44 mg/kg once daily

7 days


Panacur ***

50 mg/kg once daily

3 days



25 mg/kg bid

2 days

Note: bid = twice daily; *Maximum daily dose 200 mg; **Contra-indicated in pregnancy; ***Used for the treatment of other-worm infections. See also febantel.

It has been said that treatment of the dog can be quite effective with sulfa drugs, such as Albon™ which is a brand name for the sulfa drug sulfadimethoxine made by Pfizer. It is an antibacterial (and some say antiprotozoal) medication, targeting the secondary bacterial enteritis associated with coccidiosis in dogs. Probably, any beneficial effect comes from eliminating one of these other debilitating pathogens rather than from a direct attack on the Giardia organism. Therefore, the reports of success using it against Giardia as well as Coccidia may be due to allowing a less-encumbered body to better fend off the other problems naturally. The lower the total load of microbes or varieties, the better chance a dog will have of dealing with them. Especially important in very young puppies, bitches in season or in whelp, or any others highly stressed.

Albendazole is marketed under such names as Valbazen, Albenza, Eskazole, and Zentel. It is used to treat a variety of worm and parasitic infections. Albendazole is not commonly used for treatment of Giardiasis, though may sometimes be prescribed by a veterinarian if other medications are ineffective. Side effects include fever, nausea, vomiting, and temporary hair loss.

You might also want to ask your veterinarian about Marquis®. This was marketed as “the first FDA-approved EPM treatment combining safety, efficacy and convenience.” EPM is equine protozoal myeloencephalitis. Though this anticoccidial drug had been developed for and used in horses, in some places it is now being used in dogs. It is sold as “15% ponazuril antiprotozoal oral paste” and the active ingredient supposedly has activity against Giardia as well as the parasite that causes EPM. For dogs, the conversion is 10mg of paste to 20mg of water. The dosage is 0.2mg per pound, so a 2-lb puppy would get 0.4mg, and a 5-lb pup would get 1 gram (approximately 1 cc).

Fenbendazole (a trade-name is Panacur) in granules or powder form can be used in dogs as young as 6 weeks of age and in some studies has been shown to be 100% effective against Giardia. For many vets, it has been the drug of first choice for several parasites, and thus commonly used for general worming. Panacur is mixed with the food for 3-5 consecutive days at a dose based on the dog’s body weight; then repeated in 3 weeks.

Febantel is, for practical purposes, nearly synonymous with fenbendazole as far as the average dog owner is concerned. A veterinary scientist, or an organic chemist such as I, might distinguish between these two. But suffice it to say that either form has a wide spectrum of efficiency and efficacy against nematodes (“worms”). It has a good case history of use in sheep, cattle, horses and even humans. The difference in the structural or “molecule” chemistry (insignificant as it may be to the layman) is that febantel, a diphenylsulfide, besides being used as an anthelmintic itself, is the starting material that is used to produce broad spectrum benzimidazole anthelmintics; derivatives include fenbendazole, albendazole, and oxfendazole. The host animal acts as his own chemical factory, too, metabolizing the “pro-drug” febantel to fenbendazole and oxfendazole.

There are some other facts that may be of interest. The manufacturers of Drontal Plus state that fenbendazole is safe as well as having activity againstGiardia, so many veterinarians use a 5-day regimen instead of the approved 3-day regimen. The two-way combination of fenbendazole (Panacur) and metronidazole (Flagyl) has also shown very good results in the treatment of Giardiasis. In addition, fenbendazole/febantel also is effective against a variety of other canine intestinal parasites. Published data indicates that the pyrantel pamoate, febantel, and praziquantel three-way combination sold by Bayer Corporation as Drontal Plus is as effective against Giardiaas you can get. At present, I would choose fenbendazole (or the febantel form) as one of the first agents selected for treatment of dogs.

A final note here: the danger of pups contracting parvovirus is diminished greatly if all other health hazards have been avoided. A dog that is free of worms and Giardia, and has been robust and healthy may have better chance of avoiding parvo, and this ability increases rapidly as the dog gets a little older. Very few older pups or adults get parvo unless severely compromised by some other health problem. Likewise, once a puppy gets past babyhood, and does not have other illnesses, it becomes naturally more resistant to Giardia, and easier to treat for that.

Fred Lanting

Fred Lanting is an internationally respected show judge, approved by many registries as an all-breed judge, has judged numerous countries’ Sieger Shows and Landesgruppen events, and has many years experience as one of only two SV breed judges in the US. He presents seminars and consults worldwide on such topics as Gait-&-Structure, HD and Other Orthopedic Disorders, and The GSD. He conducts annual non-profit sightseeing tours of Europe, centered on the Sieger Show (biggest breed show in the world) and BSP.

Books by Fred Lanting