Causes of Giardia in Dogs

Giardia in dogs occurs as a result of infection with the protozoa Giardia. Giardia normally live in the small intestines of dogs and cats, without causing disease. Veterinarians disagree on the number of Giardia symptoms, the number of infections and whether or not all infections should be treated.

The Life Cycle of the Giardia Protozoa

Vets don't know a great deal about the life cycle of this protozoa. However, they do know that a dog becomes infected when it ingests the protozoa in its cyst form. When the cyst reaches the small intestines, it opens and releases an active form called a trophozoite. Trophozoites used their hairlike flagella to move around; they then attach themselves to the wall of the intestine and begin to reproduce by dividing.

Vets don't really understand when or how, but, at some stage, the trophozoite encysts (develops a tough barrier around itself) again and leaves the dog's body via the stool. Once out of the body, the Giardia protozoa can go on to infect other animals and people.

Symptoms of Canine Giardia Infection

Most Giardia infections cause no symptoms at all. It's rare for the infection to cause disease, but when it does, it usually sickens younger dogs and causes diarrhea. This diarrhea may come and go without apparent cause. It may be acute diarrhea that clears up on its own in less than three weeks, or it may be chronic diarrhea that continues for longer than three weeks.

Dogs suffering from active Giardia infection may lose weight but not their appetites. They may have pale, foul-smelling feces that is greasy in appearance.

Giardia in dogs can prevent the absorption of nutrients and otherwise interfere with digestion by damaging the lining of the intestine.

Diagnosing Giardia Infection in Dogs

It can be difficult to diagnose Giardia in dogs, because the protozoa are very, very small and they don't appear in every bowel movement. Your vet may need to perform multiple fecal examinations to diagnose Giardia. Vets use special procedures to identify Giardia. These procedures are the same as the ones used to diagnose hookworms and roundworms. These procedures kill trophozoites and can help make encysted protozoa easier to find.

Your vet will mix some of your dog's stool with water and look at it under a microscope to search for trophozoites. Because of their flagella, trophozoites can be seen moving under a microscope. Cysts are often found in firm bowel movements, and can be isolated using a special solution. Your vet will then examine the solution under a microscope.

Even interpreting the results of Giardia tests can be difficult, because Giardia is often present in the stools of uninfected dogs, and your dog's diarrhea symptoms may be caused by another disease entirely. Your vet will consider all of your dog's symptoms and his complete medical history when deciding whether or not Giardia is the cause of diarrhea. Your vet may prescribe antiparasitic and antibiotic drugs, like fenbendazole and metronidazole, for the treatment of Giardia infection.