Giardiasis in Cats Symptoms and Treatment

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Giardia in cystic stage
Giardia In Cystic Stage

While giardiasis is treatable, it can be difficult to eradicate and often spreads among groups of cats in homes or catteries. Giardiasis has symptoms similar to those of other intestinal diseases, so it must be diagnosed and treated by a vet. Cats almost always recover fully from giardiasis, though pets with underlying conditions may find it harder to recover.

What Is Giardiasis?

Giardiasis is a disorder caused by tiny one-celled organisms which live in the small intestines of cats. The severity of disease is variable, but they can cause serious illness in some infected cats, with symptoms including severe diarrhea, sluggishness, and dehydration.

Symptoms of Giardiasis in Cats

Not all cats infected with Giardia become sick, but if they do, the most common symptom of giardiasis is diarrhea, either with sudden onset or of the more chronic variety; diarrhea may be foul-smelling. Stools may be bloody or accompanied by mucous or flatulence, and the cat may lose weight, become listless, and neglect grooming. Since these symptoms may be indicative of a number of other medical conditions, including IBD and cancer, only a veterinarian can make an accurate diagnosis, through examination and tests.

short-fur white cat
short-fur white cat

Causes of Giardiasis

Giardia are one-celled organisms—neither worms, bacteria, nor viruses. There are eight giardia genotypes, A through H. Dogs are most often infected with genotypes C and D, while cats are usually infected with F. Human beings are also vulnerable to giardiasis, and can be infected with types A, B.

Giardia undergo two stages: a motile (swimming) stage and a cystic stage. Giardia cysts are the primary means of transmission from host to host. Giardia cysts are hardy, being resistant to both freezing and to chlorination of water, and can live for several months if not dried out or exposed to sunlight.

Giardia cysts are excreted (shed) in the feces of an infected cat, then picked up when ingested by other cats sharing litter boxes. The giardia make their way to the small intestines of cats, where they can cause a wide range of symptoms. Giardiasis is the name given to the infection.

sleeping gray kitten on person's hand
sleeping gray kitten on person's hand

Not all cats infected with giardia will become sick. Cats may host the organism for several years, while passing it on to other cats, before showing any clinical signs of giardiasis. An immune-suppressant factor, such as FIV, FeLV, or overall debilitation, may hasten the onset.

The incidence of feline giardiasis is relatively low in North America (about five to fifteen percent), but it can sometimes wreak havoc in catteries, shelters, and some multi-cat households; in short, wherever a large number of cats share space. Also, cats with outdoor access may ingest the organism by drinking water from a stream or pond, particularly in agricultural areas.


Giardia cysts can be identified in a fecal smear under a microscope. Since cysts are shed in stools sporadically, several different fecal samples may be needed for a positive identification. Special stains may be needed, as the organism can sometimes be elusive.

medium-fur brown and white cat sitting on brown sofa near white window
medium-fur brown and white cat sitting on brown sofa near white window

Vets may need to use a zinc sulfate flotation solution, though they may also be able to see the giardia on a smear. Another tool for identifying giardia is called an ELISA test. This test looks for the presence of antibodies to giardia in the cat's feces. Since Giardia can be hard to diagnose, a cat with giardiasis symptoms may be treated for giardia even without a definitive diagnosis on the basis of medical history and symptoms.

Giardiasis is often treated with metronidazole (Flagyl), but there are several other oral medications available including Fenbendazole. Because cats are very small, the pills are usually split, making them taste bitter; it is possible to find cat-friendly formulas that make the flavor less bitter. According to Dr. Mike Richards, cats show more resistance than dogs to medication for giardiasis, so sometimes it takes several courses of treatment or a switch to another medication to effect a cure.

Severe diarrhea and vomiting can cause dehydration, which is particularly dangerous for cats, so it may be necessary to take special steps to be sure your cat is properly hydrated during recovery.

short-fur white cat
short-fur white cat

How to Prevent Giardiasis

Scrupulous scooping, cleaning, and disinfecting of litter boxes will help prevent the spread of giardia to other cats. A 30:1 solution of chlorine bleach may be effective for litter boxes, and some catteries advocate steam cleaning of all surfaces where giardia cysts might be present.

If you do have a cat infected with giardiasis, it's important to avoid reinfection. If possible, wash the cat frequently and keep it isolated until all symptoms have cleared up.

Can Giardia Spread to Humans?

There is a human form of giardiasis which, like feline giardiasis, is also caused by drinking contaminated well water. In fact, giardia are the most common form of traveler's diarrhea.

brown and white tabby cat
brown and white tabby cat
selective-focus photography of white cat
selective-focus photography of white cat

Since there are several strains of giardia, and cats usually have type F which is not infective to humans, it is uncommon for strains to be passed from cats to people. However, in rare instances, cats can contract strain A or B, so to be safe, it makes sense to use good sanitation procedures. Wash your hands thoroughly with soap and water after cleaning litter boxes and before handling food or touching your mouth.

While a diagnosis of giardiasis sometimes strikes terror in the hearts of cattery owners and shelter volunteers, early intervention can help prevent a widespread epidemic.