Giardia | Symptoms, Diagnosis, Treatment and Transmission to Humans

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Giardia is a commonly encountered flagellate protozoan parasite that affects both dogs and cats, and that can be transmitted to humans. One of the most clinical symptoms that characterize the disease is acute small bowel diarrhea, and in very few cases, it is also associated with acute or chronic vomiting. Around one to forty percent of all dogs and cats have or have had Giardia, but many of them do not manifest any clinical signs.

In this article, we’ll look at the symptoms, diagnosis, treatment, and prognosis of this parasitic infection in dogs and cats, and we’ll also discuss some facts about how it can be transmitted to humans and what you can do to prevent this.

How Is Giardia Transmitted?

Both dogs and cats can swallow a cyst stage of this particular parasite, and if the animal is susceptible, the protozoan will pass into the intestine, turn into a trophozoite and attach to the intestinal wall to feed. Since these feeding forms reproduce by dividing, sometimes the number of trophozoites can be so high that it can affect the intestinal lining, and therefore produce severe diarrhea, some of which can even contain blood.

A number of these feeding forms turn into cystic forms, and once dogs and cats start passing them in their stool, they can infect other animals. Your pet doesn’t necessarily have to share his or her living environment with another infected animal. If you have an outdoor cat, there are plenty of opportunities for her to come in contact with the feces of another dog or cat. Your dog can also get it while sniffing the feces of another dog as you take him or her out for a walk.

There are other ways in which Giardia can get inside a dog’s or cat’s body – through contaminated water or from the contaminated ground.


One mention that we must make is that there are more than enough adult dogs and cats that never manifest any clinical signs because they are completely healthy and as such, their immune system keeps the infection under control. Despite being carriers, they can just as well never experience diarrhea.

The symptoms appear in certain debilitated categories such as puppies and kittens or old dogs and cats, whose immune systems aren’t well-developed or just aren’t capable of handling the aggression of the feeding forms we mentioned earlier on. The watery diarrhea which is the main symptom of this disease can dehydrate the animal to such an extent that it might end up being fatal.

If the pet’s immune system is immunocompromised, some of the clinical signs that you could notice are acute foul-smelling diarrhea and occasional vomiting. Cats that have FIV or FeLV are more predisposed to developing severe Giardia symptoms.

In many situations, the diarrhea could have a greenish tint or could contain blood. In some animals, the signs can persist for a couple of days and then disappear completely. Whether this happens or not, it is a good idea to take your pet to the vet’s as soon as you notice any type of diarrhea, especially if you are the parent of a puppy or a kitten.


Giardia can be discovered using a routine fecal flotation, but sometimes, this method can prove to be insufficient. You will be required to take a feces sample to the clinic so that the vet performs the flotation test and examines the feces right under the microscope. There are also tests that can be performed to determine the presence of specific Giardia antigens. If the clinic performs them, you will get the results faster, but sometimes, they have to be delivered to laboratories that process them.

In some cases, a presumptive diagnosis can be made based on the animal’s medical history and clinical signs that are specifically suggestive of this disease – greenish diarrhea, for example.


Giardia infections are fully treatable, as long as you take your pet in for a check-up as soon as possible and he or she doesn’t become severely dehydrated. There are two main medicines that are used commonly for killing Giardia – metronidazole and fenbendazole. If necessary, these two can be given in combination, especially to cats and dogs that have not responded to the initial treatment.

The problem with fenbendazole and metronidazole is that they are both very bitter, and so it is very challenging for cat parents especially to administer the treatment. To make the dosage as correct as possible, they might also have to split the coated tablets, which means that the bitterness will be exposed. No matter the problems that the pet parent might experience when trying to give the dog or cat the treatment, it must be followed for a minimum of five to seven days depending on the severity of the disease.

Supportive treatment might also be required depending on the dehydration level, in which case your pet might have to be kept at the clinic to be hydrated regularly throughout one or two days. A highly digestible diet is necessary during and following the medication. It’s important to note that your pet has to be tested again after two to four weeks after the treatment has been completed so as to make sure that the Giardia has really been killed.


In many cases, the prognosis is good. The animals that have less competent immune systems such as debilitated, very young, or geriatric pets do have a risk of developing complications, and the infection (and its consequences) can be so severe as to lead to death. That’s why it’s so important for you to take your cat or dog to the vet as soon as you notice the presence of acute diarrhea, especially a foul-smelling and greenish one.


Giardia isn’t a particularly resistant parasite, so with a few simple hygienic measures, you can make sure that your dog or cat doesn’t get it again. You have to shampoo your pet to prevent any fecal residue from remaining in his or her coat. You also have to clean and disinfect your floors, as well as any holding areas and crates that he or she uses. Finally, you can limit your outdoor cat’s or dog’s access to untreated surface waters such as ponds, creeks, or lakes to avoid re-infection.

Can You Get Giardia from Your Pets?

The risk of humans catching such an infection from cats or dogs is typically small, and that’s because the exact species that normally affects humans is different compared to that which affects pets.

You can protect yourself and your family from potential infections, however, by using several methods that mostly revolve around hygiene. Use gloves when you garden to avoid coming in contact with infected feces, clean your house surfaces on a regular basis, disinfect areas that your pet has access to (especially kids’ toys), and wash your hands often particularly after you’ve picked up your dog’s or cat’s poop or come in contact with it in some other way.

You might want to know that Giardia can survive in a contaminated environment for a good amount of time. In cold temperatures, it can survive up to seven weeks, and at room temperature, it can survive for almost a week. In water, however, it can survive for up to one to three months, especially if it is cold. That’s why it’s so important for you to avoid letting your dog drink from surface waters.


Giardia infections can affect both cats and dogs and can be transmitted to humans but in very, very few cases. The parasite affects mostly young animals and those that have a debilitated immune system. The main clinical sign that characterizes the disease is profuse diarrhea, which can be bloody or with a greenish tint.

The disease can be treated effectively as long as you take your pet to the vet right after noticing the diarrhea syndrome since dehydration can become very severe and can even put the animal’s life at risk.



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