HomeNewsNov 22, Giardia in Dogs: Another Parasite You Should Know

    Nov 22, Giardia in Dogs: Another Parasite You Should Know

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    By Janice Jones     |Last Updated 11-22-2021

    As parasites go, giardia in dogs is a particularly nasty bug that is not only difficult to get rid of but causes vomiting and diarrhea especially in young puppies

    Giardia in Dogs: cyst and trophozoite stagesGiardia in Dogs: Cyst and trophozoite life-stages

    What is this Parasite?

    Giardia in dogs is another annoying parasite that can
    affect your dog’s health.  This small
    protozoan, Giardia is not a worm, but a one-celled organism that is also
    capable of causing harm in many animals including people, although it’s not
    entirely clear how common the transmission is between dogs and people. 

    It is a very common parasite found in dogs,
    cats, horses, pigs, cows, sheep, and goats. The resultant disease is called

    How Do I and my Dog Get this Parasite?

    People get giardia when they sample contaminated
    water usually on a camping trip and the resulting vomiting and diarrhea is
    called traveler’s diarrhea. 

    If you are
    an outdoors type of person, you might have heard of beaver fever or backpacker
    disease.  These are all caused by the
    giardia organism.

    In dogs, the
    most common form of transmission is through the fecal—oral route where dogs
    either come in contact with infected feces, water, or surfaces that contain the
    giardia cysts. They can do this by eating the cysts directly, sniffing infected
    poop and then licking their lips, or drinking contaminated water.

    The infection is easy to pick up because the Giardia cysts
    are very resilient and contagious immediately after another animal has excreted

    When there is high humidity, the
    survival rate of the cysts increase and when there are more animals in the
    area, infection is inevitable.   This is why you see these infections in
    shelter dogs, pet stores, and multiple dog homes.

    Life Cycle of Giardia in Dogs

    There is much that veterinarians do not know about
    the life cycle of this one celled organism. 
    This protozoan appears to have a two stage life cycle.  

    To begin an infection, a dog ingests a cyst
    usually through eating poop, infected grass or drinking contaminated
    water.  The cyst pasts through to the dog’s
    small intestine where it opens up and releases an active version called a trophozoite.  

    During this stage, the tiny organism is motile
    and lives in the small intestine of its host. 
    Here it attaches itself and dines on the cells lining the intestines.  This causes poor digestion which leads to
    diarrhea. This stage will reproduce by dividing and then many will produce hard
    cysts around them. 

    These cysts are then
    shed in the stool where they can infect another dog or other animal that comes
    in contact with the infected feces. Once the second dog swallows the cyst, it
    migrates to the small intestine and the process begins again.

    This hardy cyst phase can exist in the environment
    for up to several months, especially in water and damp locations.

    Giardia in dogs is common, but also
    occurs in farm animals and people.  There
    seems to be different groupings of these organisms called Assemblages that
    affect different species of animals. 

    example, dogs tend to have assemblages C and D, cats are infected by A1 and F,
    and humans are normally more susceptible to A2 and B. 

    This is good news for people since it is possible
    to contract giardia from dogs, it is not likely, but again there is much to
    learn about this parasite. When humans acquire this type of infection it is
    usually as a result of coming in contact with contamination from human

    This often occurs when giardia
    enter the public water supply.  Outbreaks
    have known to happen even in day care centers where there is a breakdown in
    good hygiene practices.

    Symptoms of Giardiasis in Dogs

    • Foul smelling feces
    • Diarrhea with some mucus and/or blood
    • Vomiting
    • Sometimes Fever
    • Loss of weight if not treated

    your dog has foul smelling diarrhea, that can range from soft to watery with
    traces of mucus he might have giardia. Sometimes blood is seen in the stool.

    Vomiting is another symptom and sometimes fever.  If symptoms persist, the dog may also lose
    weight.  Often dogs that are infected
    with giardia show no symptoms at all. 

    this is not a life threatening disorder unless the dog has other underlying
    problems that might cause him to be immunocompromised. 

    of Giardia in Dogs

    will not be able to diagnosis this yourself as the parasite is microscopic and
    only detected through laboratory tests that are performed by a veterinary
    hospital or outside laboratory. Giardia is often misdiagnosed or underdiagnosed
    because it is difficult to see.

    are several ways to observe the cysts, but since cysts are not shed continually,
    it is very possible to receive several negative test results, but still have
    the disease.  

    There are several tests
    that are often used including a direct smear using a fresh, unrefrigerated
    sample, fecal flotation, and a fecal ELISA called the Snap® Test.

    a fresh sample is observed under the microscope, the more active form or
    trophozoite can sometimes be observed moving around.  When a fecal flotation method is done, the
    vet tech is looking for the cyst stage.

    both positive and negative results can be confusing.  Many dogs many shed the cysts without having
    any symptoms, whereas some who have symptoms and the disease may not shed any
    cysts on the day of the test. 

    Some veterinarians
    will repeat a test that has negative results when the dog shows the classic

    Drug Treatment for Giardia in Dogs

    Here is another area of controversy in the
    veterinary profession:  How and when to
    treat?  Some vets will treat even with a
    negative test result if the dog is showing other signs of the disease because
    there is a potential for human infection.

    There are several drugs on the market that will
    treat the infection but all require multiple days to administrate the

    Metronidazol or Flagyl

    Metronidazole is an antibiotic which is given for 5
    to 7 days.  Going by the trade name,
    Flagyl, this older treatment is about 60-70 effective for the treatment of
    giardia, but will treat other bacterial causes of diarrhea.  Side effects of this drug include vomiting,
    anorexia, and liver toxicity.  It cannot
    be given to pregnant dogs.

    Fenbendazole or Panacur

    Fenbendazole, or Panacur, is a worming medicine or antiparasitic
    that also treats other types of parasites and is given for 5 days to treat
    giardia. This is considered to be safe in young puppies at least 6 weeks old.

    Sometimes, a combination of metronidazole and
    fenbendazole are given. 

    Environmental Treatment of Giardia in

    Bathing is also required as the dog is
    being treated to remove any fecal debris and eliminate any cysts that might
    remain on the dog’s hair or fur.  When
    there are other dogs in the household, they all may be treated at the same
    time.  A regular dog shampoo is usually
    sufficient to remove all fecal debris.

    It is difficult to decontaminate soil,
    grass or remove standing water in the outdoor area.  Cysts will not survive in dry conditions, but
    prompt removal of any feces will help eliminate the problem, at least in areas
    where there is not much rainfall.  In
    moist or wet areas, it is nearly impossible to remove the threat entirely, but
    quick removal of the dog’s poop will help.

    Inside, any surfaces the dog comes in
    contact with can be cleaned and sanitized using steam cleaning or

    For disinfecting
    surfaces, such as floors or crates, you can use chlorine bleach at a rate of
    1-2 cups per gallon of water. 

    chemicals such as quartenary ammonium or Lysol work well to kill the
    cysts.  Clean, disinfect, and allow to air
    dry before allowing your dog to have access to the area.

    The longer the
    disinfectant stays on the surface the better the chances that all cysts will be
    killed.  Ten minutes is usually a good
    ball park figure to aim for if you are spray with a bleach solution.

    Public Health Concerns of Giardia in Dog

    This is still another area of
    controversy.  To be on the safe side, you
    should consider the possibility that the giardia that infects dog could
    potentially infect people. 

    Most sources,
    however, suggest that Infection is low between dogs and humans.  People who have diseases that might increase
    their susceptibility to infection should limit their exposure to dogs being
    treated for giardia.  We are including
    people in this category that are immunodeficient such as those with AIDS or
    cancer, or those who are undergoing chemotherapy. 

    If you do develop gastrointestinal symptoms
    after being exposed to an infected dog, it would be advisable to seek medical

    Always wash your hands before and after
    feeding and handling the dog and of course after cleaning up soiled areas. 

    If you have children, encourage children to
    get into the habit of washing their hands regularly especially after playing
    with their dog.

    References and Further Reading on
    Giardia in dogs

    Centers for Disease Control and

    Other Types of Parasites in Dogs

    Dog Heartworms

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