by Jennifer Chaitman, VMD, ACVIM (Internal Medicine)

Giardia is a common protozoan parasite that causes diarrhea in man and animals. It is found worldwide and is seen year round in New York City, The Hamptons and Connecticut.

Giardia is transmitted by cysts containing the organism. The organism is freed in the digestive tract. Infected dogs (and people) transmit giardia through fecal material that is then ingested by another animal. It can be through direct contamination (a dog eating another dog's stool), or by drinking water that is contaminated by stool containing giardia.

Signs of giardia are increased gas or bowel sounds, loose stool to watery foul smelling diarrhea. Some dogs vomit although this is uncommon.

Giardia is best diagnosed with an enzyme-linked immunoabsorbent assay or ELISA test. Idexx makes one and it is highly sensitive and can find giardia greater than 92% of the time. A zinc sulfate concentration technique can also be done yet it at best has a 70% chance of catching it on one sample.

Most cases of giardia are easily treated with metronidazole (Flagyl) or fenbendazole (Panacur), yet some cases are resistant to these medications or take multiple treatments sometimes with a combination of medications. Most of the hard to treat infections are found in puppies from pet shops or kennels who become infected before their immune systems are mature.

Dogs being treated for giardia should be bathed frequently during treatment to get rid of any cysts they may be carrying on their coats and the environment should be cleaned with dilute bleach. People in the household should take care handling the stool and wash their hands frequently since they can be infected through an oral-fecal route. If a person thinks they may have giardia, they should see their physician.

There is a vaccine for giardia but it is not currently recommended for routine use.


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