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Giardia duodenalis is a protozoal parasite (single celled) which can cause acute and chronic gastroenteritis. In both cats and dogs, it is a common cause of both weight loss and diarrhoea in Hong Kong.

Giardia is normally spread by the ingestion of the cysts in contaminated food and water. The cysts are found in infected faeces and are spread by the faecal-oral route. Once inside the body, the cysts will mature into trophozoites (active feeding stage of the parasite) and both cysts and faeces can be passed out in the faeces to infect other animals.

Clinical signs

Infected animals can appear to be completely healthy with no symptoms at all. However, infections can lead to intermittent or severe diarrhoea, weight loss, inappetance and occasionally vomiting. Sometime, infection may appear simply as small amounts of blood or mucus in normal stools.

Diagnostic tests

At Acorn, we use a rapid test, which can accurately detect small numbers of Giardia antigens (specific proteins) in the faeces. We also routinely analyse faecal samples visually with a microscope after preparation with zinc sulphate flotation and centrifugation (high speed spinning to separate cysts from faecal matter). This visualization allows us to see any other concurrent infections/parasites such as worms or Coccidial cysts)

Since Giardia can be shed intermittently, we may occasionally ask you to collect faecal samples for 3 days to increase the likelihood of detection of Giardia antigens.


There are many different drugs that we are able to use to treat Giardiasis. Albendazole and fenbendazole are commonly used and very effective against Giardia. Metronidazole is another frequently used medication, especially in humans – however it is less a lot less effective in animals than albendazole.  These are just a few of the many drugs available for us to use in Acorn against Giardia.

It is very important to treat all animals in the same household together against Giardia (even if not showing symptoms) to minimize the likelihood of re-infections. It is also necessary to clean the environment thoroughly with an appropriate detergent/bleach to prevent re-exposure to the parasite. Faeces should be removed from the environment as soon as possible after each defaecation.

It is very important to note that Giardia can infect humans so appropriate measures should be adopted to minimize infection such as wearing gloves and washing hands.