Giardia is a simple one-celled parasitic species; it is not a "worm", bacteria or virus. There are seven genotypes, A through G, with dogs being most commonly infected by C and D, cats with F, and humans most commonly infected with A and B. E and F are rarely reported. The parasite occurs worldwide and is a common cause of "Traveler's Diarrhea" in people. Outdoor enthusiasts who inadvertently consume contaminated water may develop "beaver fever", which is another name for giardiasis in people. Other examples of protozoan parasites that can cause enteric (intestinal) disease are Coccidia, Cryptosporidia and Toxoplasma.
Symptoms: Giardiasis can cause diarrhea, vomiting or any other signs of illness. The diarrhea may be intermittent. Most dogs do not have a fever but may be less active. The disease is not usually life-threatening unless the dog’s immune system is immature or immunocompromised.
How do dogs get giardia: A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. In susceptible dogs, once the cyst passes into the dog's intestines, it goes through a transformation to the trophozoite, or feeding form, and attaches to the intestinal wall to feed. If sufficient numbers are present, clinical signs of damage to the intestinal wall will develop. Trophozoites reproduce by dividing, and some transform into the cystic form. Eventually, the dog passes infectious cysts in its stool. The time it takes from ingestion of cysts to passage in feces is 5 to 12 days in dogs and 5 to 16 days in cats.
Example: Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water.
These cysts are immediately able to infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water.
When Giardia cysts are found in the stool of a healthy adult dog without diarrhea, they are generally considered a transient, insignificant finding. However, in puppies and debilitated adult dogs, they may cause severe, watery diarrhea that may be fatal if left untreated.
Treatment: The most common drugs used to kill Giardia are fenbendazole and metronidazole. These drugs are normally given for three to ten days to treat giardiasis. Both drugs may be given in combination if necessary. This combination is usually administered to cats with refractory diarrhea (diarrhea that hasn't responded to treatment). Supportive treatment with other drugs may be needed as supplemental therapy if dehydration or severe diarrhea is present. A low-residue, highly digestible diet may help lessen loose stools during treatment. Some dogs may require follow-up tests and treatments based on their condition and severity of infection. All infected pets should be re-tested two to four weeks after completion of treatment.
The time it takes from ingestion of cysts to passage in feces is 5 to 12 days in dogs and 5 to 16 days in cats.