What are giardia?
Giardia are single-celled protozoa, infectious to many types of animals (including humans) all over the world. Their presence in the host intestine can cause diarrhea, though some hosts are symptom-free carriers. Giardia have two forms: the trophozoite and the cyst. The trophozoite (or "troph" for short) is the form that lives within the host, swimming around and attaching to the intestinal wall. Trophs are passed in feces and must develop into cysts and form a shell if they are to withstand the temperature/moisture variability of the outside world. Cysts are the contagious stage. Trophs are the parasitic stage.
What is the life cycle of a giardia organism?
As mentioned, trophozoites are passed in fresh feces but promptly round up into hard-shelled little cysts so as to withstand the conditions of the outside world. The cysts live in the environment (outside the host's body) potentially for months until they are consumed by a host. Inside the host, the cyst's shell is digested away releasing trophozoites into the intestine and the cycle begins again. Contaminated water is the classical source of a Giardia infection.
When a fecal sample is analyzed, the appearance of the Giardia organism depends on whether the sample is freshly obtained or if it has been outside of the host's body for a while. Giardia organisms begin to round up into cysts in a matter of hours. The active trophozoites rather look like funny faces with the 2 nuclei forming the eyes and median bodies forming the mouth. Cysts look a bit more generic.
In the environment, cysts survive in water and soil as long as it is relatively cool and wet. A host will accidentally swallow a cyst when drinking from a puddle, toilet, or when licking his or her fur. After the cyst has been swallowed, the cyst's shell is digested away freeing the trophozoites who go forth and attach on the intestinal lining.
After infection, it takes 5-12 days in dogs or 5-16 days in cats for Giardia to be found in the host’s stool. Diarrhea can precede the shedding of the Giardia. Infection is more common in kennel situations where animals are housed in groups.
How does giardia cause diarrhea?
No one is completely sure but infection seems to cause problems with normal intestinal absorption of vitamins and other nutrients. Diarrhea is generally not bloody. Immune suppressive medications such as corticosteroids can re-activate an old Giardia infection. We do not know why some infected hosts get diarrhea while others never do.
How is giardia diagnosed?
Giardia shed organisms intermittently and may be difficult to detect. Sometimes pets must be retested in order to find an infection and asymptomatic carrier animals are common. A fresh fecal sample sent for analysis is the best way to detect an infection.
What is the treatment for giardia?
A broad spectrum dewormer called fenbendazole (Panacur®) seems to be the most reliable treatment at this time. Metronidazole (Flagyl®) in relatively high doses has been a classical treatment for Giardia but studies show it to only be effective in 67% of cases. For some resistant cases, both medications are used concurrently. Febantel is also commonly used for Giardia as it is converted to fenbendazole in the body.
Because cysts can stick to the fur of the infected patient and be a source for re-infection, the positive animal should receive a bath at least once in the course of treatment. At the very least, the patient should have a bath at the end of the treatment course.
Can humans get giardia?
The short answer is only rarely so concern is pretty low in general.
To play it safe, wear gloves to dispose of animal fecal matter and always thoroughly wash hands before eating.
Environmental Decontamination
Giardia cysts are killed in the environment by freezing temperatures and by direct sunlight. If neither of these are practical for the area to be disinfected, a chemical disinfectant will be needed. The most readily available effective disinfectant is probably bleach diluted 1:10 in water which required less than one minute of contact to kill Giardia cysts in one study. Organic matter such as dirt or stool is protective to the cyst so on a concrete surface basic cleaning should be effected prior to disinfection. Quaternary ammonia compounds can also be used to kill Giardia cysts.
Animals should be thoroughly bathed before being reintroduced into a “clean” area. A properly chlorinated swimming pool should not be able to become contaminated.