Treating Giardia in Cats

Source: PetWave, Updated on July 16, 2015


Giardiasis, sometimes called “Beaver Fever”, is an infection by Giardia - a tiny, one-celled motile protozoan parasite that lives in the gastrointestinal tract of people and most domestic animals. Cats are less commonly clinically infected than are dogs, and young animals of all affected species much more commonly show outward signs of clinical disease. Mammals become infected by ingesting the cyst form of the parasite from water, food or fur that is contaminated with infective fecal matter. Giardia is found throughout the United States and in many other parts of the world. Many cats infected with this parasite are asymptomatic. However, kittens and older cats with weakened or stressed immune systems can have severe reactions to Giardia, including loss of appetite, malnutrition, foul-smelling diarrhea, bloody or pale-colored and greasy stools, weight loss and weakness. In cats, these signs are consistent with large bowel inflammation. With chronic infection, the organism eventually damages the intestinal lining, disrupting digestion and using up nutrients necessary for normal health. When present, diarrhea usually causes dehydration. Again, although infection with Giardia is common, disease is uncommon in cats.

Treating Giardiasis

Fortunately, Giardiasis usually can be diagnosed through multiple microscopic fecal examinations done by a veterinarian on stool samples taken sequentially over several days. A recent diagnostic test (an enzyme-linked immunosorbent assay - ELISA - test) is now commercially available and makes the organisms easier to detect. While there are several medications that are effective against this parasite, it is essential to obtain an accurate diagnosis from your veterinarian before any treatments begin. Moreover, because it is possible for Giardia to be transmitted between cats and dogs, and possibly between pets and people, there may be an additional incentive to treat cases in cats with no clinical signs. The goals of treatment are to eliminate any clinical signs of infection and eliminate or at least manage the shedding of the infective cyst stage of the organism.

The antibiotic drug, metronidazole, and the anti-parasitic drug, fenbendazole, are the most frequently-used treatments for Giardiasis in companion animals. Fenbendazole is reportedly safe, effective and preferred for use in cats. Albendazole, an alternative to fenbendazole, is also effective but is not highly recommended for use in cats as it has been associated with liver damage and birth defects. Many veterinarians will not prescribe these drugs unless and until the cat develops signs from the infection. Metronidazole also has a very bitter taste, making it difficult for many owners to administer to cats. There is a killed vaccine that has proven helpful to reduce the severity of symptoms in dogs. Unfortunately, it has not been effective in reducing infection or fecal shedding of infective cysts in cats. Cats with asymptomatic latent infection remain a source of potential infection for other animals.


Since Giardia is transmitted through direct or indirect contact with contaminated water, food, fur or feces, the best prevention is to remove cats from situations where they can come into contact with those things. Any areas that come into contact with animal feces should be thoroughly and regularly cleaned and disinfected. Catteries are especially at risk. You should have your veterinarian test your cat’s stools on a regular basis, especially at the end of summer after the hot season, if you suspect possible internal parasites.

Zoonosis Note

It does not appear that Giardia can be transmitted from cats to people, or vice versa, because the particular organism in cats appears to be host-specific. Nonetheless, until we know definitively otherwise, it is prudent to consider that an infected cat might pass the infection on to people in the household, and that people may pass the infection to their pets. People also get Giardia infections directly from contaminated water supplies, usually due to less-than-optimal hygienic conditions (including human sewage effluents). In rural settings, beavers often are blamed for contaminating water supplies – hence, the occasional term “Beaver Fever”, although this association is not a significant contribution to Giardiasis today.

Popular Cat Health Topics