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Giardiasis: Diagnosis, Treatment, and Prevention

What is Giardiasis?

Giardiasis is an intestinal infection caused by a parasitic protozoan (single celled organism) called Giardia lamblia. These protozoans are found in the intestines of many animals, including dogs and humans. This microscopic parasite clings to the surface of the intestine, or floats free in the mucous lining the intestine. Veterinary research documents suggest that 5% to 10% of all dogs in North America have giardiasis at any given time.

Surveys also show that about 14% of the adult dog population and over 30% of dogs under one year of age were infected at some point during their life, and thus contributed to passing along this intestinal infection to other dogs. Another Vet research article I found suggests that 100% of kennel dogs, 50% of pups, and 10% of well-cared for dogs carry giardia.

Life cycle of Giardia

        Giardia occur in two forms: a motile feeding stage that lives in the intestine, and a non-motile cyst stage that passes in the feces. The giardia trophozoite - which is the active stage of the organism - inhabits the small intestine of the dog. The trophozoite stage is tear-drop shaped, binucleated, and has four pairs of flagella. It attaches to the cells of the intestine with its adhesive disc and rapidly divides to produce a whole population of trophozoites. As they detach they may be swept down the intestine. If intestinal flow is fast then they may appear in the feces. However, if they have time, encystment occurs as the parasite travels to the large intestine. The cyst  is fairly resistant, and can survive for several months outside of a host's body as long as sufficient moisture is provided. The cyst is oblong in shape with four nuclei that are sometimes distinctly visible. Mature cysts are usually found in the feces of infected animals. Other animals become infected by ingesting the cysts that passed from the body in feces. These ingested cysts then break open inside the small intestine to release the motile feeding stage (trophozoite). Giardia increase their numbers by each organism dividing in half which is called binary fission.
How did my dog get Giardia?
Giardia lives and reproduces in the small intestine of host animals.  Giardia trophozoites, the free living stage of the organism, form infective cysts that are passed out in the feces.  If the cysts are present in a wet or damp environment they can survive in a viable state for a few weeks to several months.  Giardia infections are transmitted via ingestion of trophozoites or cysts in contaminated water or food. If a giardia cyst is ingested, the cyst wall is broken down during the digestive process and the trophozoite stage begins to colonize the upper small intestine. Transmission also occurs by direct contact, especially with asymptomatic carriers. More recently, giardiasis has also been recognized as being able to be sexually transmitted. Giardia is so prevalent throughout North America because it is highly contagious. The ingestion of as few as one or more giardia cysts may cause the disease, as contrasted to most bacterial illnesses where hundreds to thousands of organisms must be consumed to produce illness.

What harm does Giardia do to my dog?

        Giardia causes its unpleasant effects on the body not by invading the tissues, but simply by being in the way. It multiplies to the point where it sort of paves the lining of the intestine and blocks normal digestion (malabsorption). This causes only partially digested food to get lower in the digestive tract than it should, causing diarrhea.

(Photo on Right). Scanning electron micrograph of giardia attached to the inner surface of the intestine.

What are the clinical signs associated with infection?

        The trophozoites divide to produce a large population, then they begin to interfere with the absorption of food. Clinical signs range from none in asymptomatic carriers, to mild recurring diarrhea consisting of soft, light-colored stools, to acute explosive diarrhea in severe cases. Other signs associated with giardiasis are weight loss, listlessness, fatigue, mucus in the stool, and anorexia. These signs are also associated with other diseases of the intestinal tract, and are not specific to giardiasis. These signs, together with the beginning of cyst shedding, begin about one week post-infection. There may be additional signs of large intestinal irritation, such as straining and even small amounts of blood in the feces. Usually the blood picture of affected animals is normal, though occasionally there is a slight increase in the number of white blood cells and mild anemia. Without treatment, the condition may continue, either chronically or intermittently, for weeks or months.

How can I be sure my dog has Giardia?

        Diagnosing giardia is not easy. Diagnosis can be done in one of two ways: via fecal sample by a Vet or via educated evaluation of clinical findings by the breeder/owner or the Vet. Via fecal sample is not straightforward. Even when a flare is at it's worst, the cysts will not be shedding in every single stool. Therefore, a negative report does not rule out giardia. The most thorough way to assess is to collect a sample from every single stool produced for 48 to 72 hours and have a Vet examine it using the giardia test kit.

The giardia test is a monoclonal antibody-based ELISA for the rapid detection of Giardia lamblia cysts antigen in stool specimens and serves as an in vitro aid in the diagnosis of giardiasis.


  • Rapid (results in < 1 hour)
  • Specific for giardia
  • Easy to perform
  • High standardized
  • Microwell format

        For what its worth, my own observation is that stools that are bloody and full of mucous are most likely to contain cysts. Via clinical findings is the other way to diagnose. This means the breeder/owner or Vet takes a look at the dog, evaluates the history and symptoms, and treats on that basis. If the treatment is successful, the diagnosis was accurate.

How can infection be treated for less?

        Infection may be treated using one of a number of different drugs that are available through Vet Supply Stores. The treatment of choice is often with Metronidazole (brand name Flagyl). Metronidazole has two interesting properties--the action is largely confined to the gut and it also seems to stimulate the local immune system. Metronidazole kills off the giardia and reduces the numbers to the level the dog's immune system can handle. This is my first choice for treating giardiasis in Beagles. I purchase the Metronidazole tablets from from Lambert Vet Supply without a prescription and for a lot less money. I have seen Vet bills charging as much as $15.00 for two (2) 250 mg tablets. I buy a product called FISH-ZOLE which is simply the prescription Metronidazole (Rx) bottled and labeled for fish tank use. It is a bottle of 250 mg x 100 tablets of Metronidazole (Flagyl) for only $11.17 (current price as of 04/20/2008). These tablets are the exact same tablets that you get when your Vet prescribes this drug to your dogs. Let me make this clear, these are the exact same tablets: same size, same color, and even same markings. Recommended Dosage:  I give adult Beagles (avg. 25 lbs) one 250 mg tablet twice per day and Beagle puppies (avg. 8-12 lbs) one-half of a 250 mg tablet twice per day for a total of 5 days. In 5 days, your Beagles will be 100% FREE from giardiasis. These tablets are extremely easy to administer, and this is also the dosage which is recommended by most Vets. You will not find this medication cheaper anywhere else. Click on the picture of the FISH-ZOLE bottle to the left of this paragraph and order several bottles today. (NOTE: Lambert Vet Supply strives to promote healthly animals and help customers save lots of money on animal health care products. Here is more information about Lambert Animal Health Care, LLC.)

          Alternatively, you may want to use Fenbendazole (Safe-Guard) since you are likely already purchasing large amounts of this inexpensive and very safe medication as a treatment for deworming your dogs. This is the second favorite treatment that I use in my kennel and you can also check out the article Canine Intestinal Worms and Inexpensive Treatment to learn more about Fenbendazole and place an order for it. The exact same dosage and three-day deworming treatment using Fenbendazole for deworming Beagles will also rid your hounds of the giardia protozoan.

          Treatments from the Vet research literature that I found are shown in the table below. Whatever treatment is chosen, it is very unlikely to eliminate 100% of the infection in all dogs. Adaptations that may be made to try to improve the success rate of a treatment regime include extending the duration and dose of the treatment. Care must obviously be taken with this approach to make sure that an adequate safety margin is always maintained. Another approach is to retreat after an interval of one week. Alternatively, repeat fecal samples may be collected one week after the treatment and dogs which are still passing cysts can be identified and treated. It should be recognized that, when treating a large number of dogs, whichever of these treatment strategies is adopted, there may be one or two dogs that remain as carriers of infection that will act as a potential source for reintroducing the infection into your entire kennel.

Treatments for giardiasis in dogs.
This information is taken straight out of the Vet Medical Manual.

Drug Name Trade Name Dose Rate Duration of
Metronidazole Flagyl 11.5 to 15 mg/lb BID** 5 days
Furazolidone Neftin 2 mg/lb BID* 10 days
Tinadazole - 22 mg/lb once daily 7 days
Fenbendazole Safe-Guard or Panacur*** 22.5 to 25 mg/lb once daily 3 days
Albendazole Valbazen 12½ mg/lb BID 2 days
Bid Twice Daily
* Maximum daily dose 200 mg
** Contraindicated in pregnancy
*** Licensed for the treatment of worm infections in dogs

I highly recommend that you also check out the article Coccidiosis: Diagnosis, Treatment, and Prevention to learn more about the other common protozoal infection called coccidiosis. No matter which treatment you choose to utilize, the simple fact is that it may not kill all of the cysts. A certain number of them can burrow into the lining of the intestines and go dormant. They can stay dormant for years. Due to the hard shell protecting the cysts, it is almost impossible to kill them when they are encysted in the lining of the intestines. Therefore, during times of stress, the cysts may re-activate and start to reproduce, causing another outbreak of giardiasis in your Beagle or Beagle kennel. The amount of stress needed to cause a flare seems to be highly variable with different dogs and dog breeds. Beagles are one of the hardiest breeds since they were developed as hunting hounds.

        Important Note:  A healthy dog may have been infected years before and never have shown any symptoms (asymptomatic carrier). They may occasionally shed very low numbers of cysts in stools--evaluating every stool (the WHOLE stool) for something like six months is supposed to be the conclusive way to rule out an asymptomatic carrier (someone did this with a couple dogs for a study). This would cost literally thousands of dollars! Not exactly a practical way to test. Therefore, if you suspect a protozoal infection in your Beagle(s), I recommend all of your dogs be treated for both coccidia and giardia at the same time since both protozoal infections have the exact same clinical signs and both are highly contagious.

How to eliminate giardia from your kennel or home?

Once infection is present in a kennel, control may be approached in two ways:-

1. identification, isolation and treatment of infected dogs.

2. mass treatment of all dogs.

        Option 1 is only practical where a few dogs in a discrete area have been identified as being infected and where complete isolation is feasible, either within their own block or in a specific isolation block. Such isolation includes segregation of exercise areas and these animals should be fed and cleaned after all others on the premises, preferably using separate cleaning and feeding equipment and separate staff if possible. Treatment of all dogs should commence on the same day when option 2 is adopted.

        Thorough cleaning of all kennel areas where infected dogs have access is essential. Once organic debris has been removed, thorough disinfection will help to further reduce the level of environmental contamination and reduce the risk of dogs becoming re-infected after the completion of treatment. Disinfectants containing quaternary ammonium compounds have been found to kill giardia cysts at the manufacturers' recommended dilutions (dilutions of one disinfectant up to 1:704 were found to be effective at both low and high environmental temperatures). I disinfect all my kennels twice per month by washing everything down with a mixture consisting of 8 ounces of Clorox bleach per gallon of water. Make sure you let it set at least 20 minutes, rinse thoroughly, and then let it get completely dry before letting your Beagles use the kennels again.  Important Note:  The efficacy of killing is increased by prolonged contact time, therefore disinfectant solution should be left for 20 minutes to half an hour before being rinsed off kennel or run surfaces. Since disinfection of grass runs is impossible, such area should be regarded as contaminated for at least a month after infected dogs last had access.

        Introduction of new dogs into the infected area should be avoided until the period of treatment and fecal sample checking has been completed. It should not be overlooked that some of the infected dogs may continue to excrete low numbers of cysts even after all treatments and examinations have been completed. It is therefore important that rigorous disinfection is maintained and a careful check is kept on the condition of all treated and introduced animals.

The following are recommendations for eliminating giardia from kennels:

  • treat all dogs with Metronidazole for 5 days or Fenbendazole for 3 days (Fenbendazole is even safe to use on pregnant and lactating bitches)
  • disinfect kennel areas, etc, with quaternary ammonium disinfectants which are effective in inactivating giardia cysts
  • bathe dogs with shampoo to remove all fecal matter, rinse with water
  • rinse dogs with quaternary ammonium disinfectants, then water
  • allow kennels to dry thoroughly for several days
  • retreat with Metronidazole (Flagyl) for 5 days or Fenbendazole (Safe-Guard) for 3 days
  • treat any new dogs with Metronidazole for 5 days or Fenbendazole for 3 days even if they test negative for giardia because it is so hard to detect in fecal tests

How can infection be prevented?

        It is very difficult to prevent the entry of an infection that is known to be carried by a percentage of normal dogs into a kennel. However, an initial period of isolation for all new entrants into kennels, for perhaps ten days, would reduce the risk of an infected dog spreading a large number of cysts around the main kennel area. All dogs could be observed and any infection present, which in the case case of giardia might be exacerbated by the stress of entry in kennels, could be identified and treated before entry into the main kennels.

        Dogs should be prevented from access to foul water that may contain large numbers of cysts (e.g.: river-flooded paddocks). Small numbers of cysts may occasionally be present in the potable water supply but the risk of this being a major source of infection is small. It is best to use chlorinated water for your dogs drinking water as much as possible. If you are using non-chlorinated water from a well, lake, or stream, you need to chlorinate the water yourself. To chlorinate drinking water: Use only liquid bleach that contains 5.25% sodium hypochlorite as its only active ingredient - no soap. Use a scant 4 drops of Clorox bleach per quart of water or 2 teaspoons per 10 gallons. As an alternate method of purification, you can also boil all of your dog's drinking water. To make sure the water is completely free from living bacteria and protozoans, you need to bring the water to a rapid boil for a minimum of five (5) minutes. Remember, cool moist conditions favor the survival of the organism; therefore, simply by keeping everything clean, disinfected, and dry you will be getting a lot further toward exterminating this nasty little one-celled parasite.

        Remember,  coccidiosis and giardiasis are both very common protozoal infestations that have the exact same clinical symptoms; therefore, I recommend that both protozoans get treated one right after the other:  coccidia for 10 days and then giardia for 5 days. Once again, I treat coccidiosis with Sulfadimethoxine (Albon) and giardiasis with Metronidazole (Flagyl), which is my 1st choice, or Fenbendazole (Safe-Guard), which is my second choice. If you are using Fenbendazole as a deworming treatment, then you are already attacking any giardia protozoans in your dogs. I deworm all hounds during the first three days of every other month using Fenbendazole (Safe-Guard). This is the exact same, three-day Fenbendazole treatment recommended by many Vets for ridding your animals of giardiasis. For more information on using Fenbendazole as a very effective, yet inexpensive dewormer read my article:  Canine Intestinal Worms and Inexpensive Treatment.

Finally there is a vaccine!!!

        Now there is a vaccine to prevent signs of disease associated with Giardia infection in dogs. Fort Dodge Animal Health was recently granted a license by the USDA for Giardia Vax®, the first vaccine to prevent disease and reduce cyst shedding caused by Giardia infection in dogs. Giardia Vax has been proven to be an aid in the prevention of disease caused by Giardia infection. Giardia Vax is safe and effective for healthy dogs eight weeks of age or older. I purchase the Giardia Vax from Lambert Vet Supply. They sell a box of 25 shots for $150.75 which figures out at $6.03 per shot (current price as of 04/20/2008). You can order a box of Giardia Vax by simply clicking on the picture of the Giardia Vax which is located below of this paragraph.

          To completely clear your Beagle kennel of the protozoan giardia once and for all, give all Beagles (adults and pups) a 5 day treatment of Metronidazole (Flagyl), followed up by a shot of Giardia Vax. Then give your Beagles an annual booster of Giardia Vax and giardiasis will be gone for good from your hounds. I highly recommend that all Beaglers order this vaccine and do the shots yourself. Giardiasis has been the most common protozoan infection in North America for the past 20 years. It is a very, highly contagious intestinal infection and is carried by both humans and all warm-bloodied animals. Be on the safe side and have your Beagle(s) vaccinated against this troublesome organism.

Image provided by Wikipedia commons under a Creative commons attribution licence.

Should you have a concern regarding the health of your Beagle(s), you should contact your veterinarian. All information on this site is presented solely for educational and informational purposes and should not, at any time, be considered a substitute for seeking or receiving veterinary care for your Beagle(s).