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What is Giardia?

Giardia duodenalis is a protozoan parasite that can infect many species including dogs, cats, wildlife, and humans. Pets can develop signs of illness, or they can be carriers of the infection showing no symptoms at all.

Giardia has many subtypes named A through to G, some of which are species-specific, so it is rare for pets to spread Giardia to humans, and not common for dogs to spread Giardia to cats or vice versa. However certain subtypes are not species-specific, so can infect other species.

How do pets contract Giardia infection?

Transmission of Giardia is through the faecal-oral route, by infected feces that contain cysts.

It can be caught in the environment and can be anywhere the infected faeces is found, for example in contaminated water or food, infected dogs, or environments.

Giardia cysts can survive a long time outside especially in cool, damp places. Once ingested the Giardia inhabit and stick to the small intestine of the host where they turn into a trophozoite. The trophozoite is responsible for the signs of the disease, they then reproduce in the small intestine of the host, and the cysts are then shed in the host's faeces.

The shedding of cysts varies, it can be continuous over several days or weeks, or intermittent which is most commonly the case in chronic cases of Giardia. The intermittent shedding can make it difficult to diagnose as some infections can be missed due to lack of shedding at the time of testing.

What are the clinical signs of Giardia?

In symptomatic pets, signs of Giardiasis can be chronic diarrhoea which is very watery, foul-smelling, malabsorptive diarrhoea. The diarrhoea can be accompanied by flatulence (wind), weight loss, vomiting, and lethargy.

Animals most at risk of clinical disease would be young and elderly pets, pets that have existing gastrointestinal health issues, or those that are immunocompromised.

How do you diagnose Giardia?

Diagnosis of Giardia in cats and dogs is through faecal tests. One method is by microscopic testing of a direct faeces smear or via a faecal flotation test.

Another method is a snap antigen ELISA test which is quick and easy to run in the clinic. Due to the intermittent shedding of cysts, to avoid missed infections it is recommended to obtain several faecal samples, ie. collect three samples over three to five days.

Given that some animals can be carriers of Giardia and that Giardia cysts are intermittently shed in faeces, these tests can produce false positives and false negatives. It is advised to run them in combination to best ascertain the degree of cyst shedding and if infection elimination is taking place.

Repeat testing is advised in pets where clinical signs have not improved to see if the infected has been eliminated.

Testing for reinfection can be conducted at two to four weeks after completing treatment.

How is Giardia treated?

Non-symptomatic carriers of Giardia are generally not treated, however, the exceptions would be in households with risk of spreading to another at-risk host be it a pet or human, or in situations of large population risks ie. Kennels, catteries etc.

Pets with symptoms of Giardia can be treated medically. Treatment is mostly based on reducing the clinical signs such as the diarrhoea, versus stopping the shedding of cysts completely. The resolution of clinical signs will then in turn reduce the shedding of cysts into the environment.

In conjunction with treatment, good personal hygiene practice is an essential component in controlling the disease and limiting its spread from pets to humans.


Washing the infected pet should be done during and at the end of treatment to remove any cysts from faecal contamination on the fur. This helps reduce a source of reinfection if cysts are licked off by the host, and reduces a source of infection to other hosts.


Feeding a high fibre diet has been found to help to control the diarrhoea symptoms and helps prevent attachment of the giardia in its parasitic stage from attaching to the lining of the small intestine.


Fendbenazole is an oral deworming medication used commonly to treat a number of parasites. For treatment of Giardia, and is generally given for three to five days. Fendbendazole is the mainstay of Giardia treatment.


Metronidazole is an antibacterial and antiprotozoal agent which can be used to treat giardiasis. It can be used in combination with Fendbendazole in resistant cases.

How can you prevent Giardia?

Environmental management of giardia helps reduce the transmission of infected cysts, this is especially important in high-population areas such as kennels. Ways to reduce environmental exposure can include the following:

  • Removing faeces from the environment to reduce exposure to infected faeces, i.e. picking up faeces on dog walks or in the yard and disposing of it in bins, daily removal of faeces from litter trays.

  • Cleaning of concrete surfaces prior to disinfecting or steaming, and subsequent drying of environmental helps reduce the environmental load in areas such as yards or kennels.

  • Direct exposure to sunlight and freezing temperatures destroy environmental cysts.

  • Regular washing of feed and water bowls with hot water and disinfectant soap.

  • Washing pet bedding and toys on a hot cycle (60°C or above).

  • Washing infected and exposed pets with shampoo to remove contaminated faeces and cysts from their coat.

  • Screening new animals before introducing them into the group, and treating them if necessary.

  • Practicing good personal hygiene and washing hands between handling animals and eating.

If you are concerned your pet may have giardiasis, the first thing to do is take a stool sample along with your pet to the vet for a check-up and testing. Giardia can be difficult to fully eliminate especially if you have multiple pets in the home, and poses a risk to human health. Therefore knowing if your pet has Giardia so you can start treatment as soon as possible is a very valuable piece of information.

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