Giardia in Dogs

What are Giardia? Giardia are sometimes confused with worms because they invade the gastrointestinal tract and can cause diarrhea. They are not worms; instead, they are one-celled parasites classified as protozoa. Most dogs that are infected with Giardia do not have diarrhea or any other signs of illness. When the eggs (cysts) are found in the stool of a dog without diarrhea, they are generally considered a transient, insignificant finding. In puppies and debilitated adult dogs, they may cause severe, watery diarrhea that may be fatal. How did my dog get Giardia? A dog becomes infected with Giardia when he swallows the cyst stage of the parasite. Once inside the dog's intestine, the cyst goes through several stages of maturation. Eventually, the dog is able to pass infective cysts in the stool. 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 a microscopic examination of a stool sample. The cysts are quite small and usually require a special floatation medium for detection, so they are not normally found on routine fecal examinations. Occasionally, the parasites may be seen on a direct smear of the feces. 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 stool exam, but it requires several days to get a result from the laboratory performing the 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 diarrhea and dehydration occur. If metronidazole is not effective, others are available. Can humans become infected with Giardia? Giardia can also cause diarrhea in humans. Environmental disinfection is very important. The use of chlorine bleach, one cup in a gallon (500 ml in 4 liters) of water, is effective if the surfaces and premises can be safely treated with it.