Coccidia and Giardia – The “Non-Worm” Parasites

by Dr. Yung

If they aren’t worms, what are Coccidia and Giardia?

Giardia and Coccidia are intestinal parasites.  However, unlike what we commonly consider a “worm” – like roundworms, hookworms, whipworms and tapeworms – giardia and coccidia organisms are small, microscopic organisms that do not develop into visible worms.

Giardia organisms are protozoan parasites that, when mature, have two little tails, called ‘flagellas’, that are the mode of movement.  These more mature trophozoites harbor in the intestines and cause gastrointestinal (GI) illness.  There are many species of giardia, and some are species-specific, meaning they will only cause illness in that particular species, but many can cross species lines to cause illness in say, both a dog and a human.

Coccidia organisms are single-celled parasites that infect and reproduce inside intestinal cells.  As these organisms reproduce, they kill the intestinal cells as they divide.  Like giardia, there are several types of coccidia, and for dogs and cats a subset called isospora is the infective species.

What are the symptoms?

Both giardia and coccidia cause varying degrees of diarrhea.  Giardia diarrhea can run (pun intended) from mild soft stools to voluminous mucousy stool.  Giardia can also cause nausea and minor vomiting in some dogs.

Coccidia can vary from being somewhat asymptomatic in a mature animal (with a mature immune system), to severe and profuse watery diarrhea with or without blood in puppies and kittens.

How does a pet get these parasites?

Like most other intestinal parasites, the primary route of infection is through a fecal-oral contamination.  Giardia cysts, which are the “eggs” of the parasite, are shed from the fecal material of an infected animal and contaminate the environment.  Giardia cysts can survive for a significant period of time in a cool and wet environment (love that rainy Oregon weather!), so contaminated water and water sources are the most common sources of infection.

Coccidia/isospora oocytes are also shed from the stool of an infected pet.  These oocytes mature in the environment and are ingested when a pet licks or grooms infected dirt off their fur.

Who gets these parasites?

Giardia affects pets of all ages.  Dogs are very commonly affected in our area, cats are less so (they likely have a better immunity to giardia).  In theory, an animal’s immune system will develop a degree of immunity after infection with giardia.  However, we still see recurring giardia infections, likely due to:

1. The immunity is not complete and/or
2. There are several species of giardia, each of which requites it own type of immunity.

Coccidia can cause significant illness in puppies and kittens.  The diarrhea can be so severe that the small puppy or kitten can quickly become dehydrated.  In a mature animal with no signs of GI illness, who does not have contact with a young puppy or kitten that could become infected, a positive coccidia/isospora fecal exam may be incidental, and may not require treatment.

How do I know if my pet has giardia or coccidia, and how do you treat it?

A fecal exam is performed to look for the giardia cysts or the coddician oocysts.  In the past, diagnosis of giardia was difficult because the cycsts can be sporadically shed, so if you tested an infected pet at a time when cysts were not being shed the pet would test negative despite being infected.  Recently, our detection of giardia has been greatly enhanced by the availability of an ELISA test, which tests the fecal sample immunologically for giardia proteins, instead of looking for the actual cysts.

Giardia is often treated with a round of fenbendazole dewormer, and sometimes with the anti-bacterial metronidazole in severe cases.  Because the giardia cysts shed in hundreds, it is often helpful to bathe the pet once or twice during the treatment time, particularly around the tail feathers, to prevent re-infection.

Coccidia is treated with coccidiostats.  These medications halt the reproductive cycle of the coccidia organisms and allow the animal’s own immunity to finish combating the parasite.  We typically prescribe a sulfa-type antibiotic for coccidian/isosporan infections in puppies and kittens.

Rarely does giardia itself cause diarrhea or GI signs so severe that it requires more treatment.  Coccidia, however, can cause severe dehydration in puppies and kittens due to the tremendous water loss and sloughing of intestinal cells.  These pets may require hospitalization for fluid therapy.

We recheck a fecal sample about a week or two after the last dewormer dose to confirm resolution of the infection.

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