Giardiasis

What are Giardia?

Giardia is sometimes confused with worms because they invade the gastrointestinal tract and can cause diarrhoea. They are not worms; instead, they are one-celled parasites classified as protozoa and have been largely overlooked until recently.

Most dogs that are infected with Giardia do not have diarrhoea or any other signs of illness. When the eggs (cysts) are found in the faeces of a dog without diarrhoea, they are generally considered a transient, insignificant finding. However, in puppies and debilitated adult dogs, they may cause severe, watery diarrhoea that may be fatal. In a recent survey in Perth approximately 21% of healthy adult dogs and 50% of puppies were found to be infected.

How did my dog get Giardia?

A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. Once inside the dog's intestine, the cyst goes through several stages of development.  Eventually, the dog is able to pass cysts in the faeces. These cysts lie in the environment and can infect other dogs. They may also be transmitted through drinking infected water.

How is giardiasis diagnosed?

Giardiasis is diagnosed by performing microscopic examination of a sample of faeces. The cysts are minute and require special techniques for their detection. Occasionally, the parasites may be seen on a direct smear of the faeces. A blood test is also available for detection of antigens (cell proteins) of Giardia in the blood. This test is probably more accurate than the faeces examination and is increasingly available as an in-house test.

How is giardiasis treated?

The typical drug used to kill Giardia is metronidazole, an antibiotic-type drug. It is given for 5-7 days. Other drugs are also used if diarrhoea and dehydration occur. If metronidazole is not effective, others drugs such as fenbendazole may be used.

Can humans become infected with Giardia?

Giardia can also cause diarrhoea in humans and children are especially susceptible. Therefore, environmental disinfection is important. The use of chlorine bleach, approximately one cup (250 ml) in 5 litres of water, is effective if the surfaces and premises can be safely treated with it. If in doubt, please contact us. Other disinfectant agents are available.