If your cat suffers from chronic or sporadic diarrhea, the cause might not necessarily be something he ate. It could result from giardia, a protozoal parasite. Symptoms of giardia infection, or giardiasis, more often appear in kittens and geriatric cats, and those with compromised immune systems. What's worse is that giardia is zoonotic, which means your cat can pass it on to you.
Grooming Raises the Risk
Giardia, found worldwide, causes diarrhea. Infected animals shed giardia offspring, cysts, in their feces. Cats can become infected by consuming the cysts when drinking water or food contaminated with feces, or by coming into contact with infected stool. Cats lick themselves frequently for cleaning, so they're at risk of passing cysts from the paws into their intestines.
Diarrhea May Come and Go
Giardiasis reveals itself primarily in your cat's feces. Symptoms include exceptionally bad-smelling diarrhea, with the stool often watery, pale, blood-tinged and greenish. The feces might contain mucus. Some cats experience vomiting and weight loss. The diarrhea might wax and wane over several weeks. Affected cats often become lethargic. Humans can contract giardiasis, so always use disposable gloves when cleaning cat litter. Some infected cats never show any symptoms but can still infect other animals and people.
Cross-Testing Curbs Misdiagnosis
You'll need to bring your cat's stool sample to the vet for giardia testing. However, making a definite diagnosis isn't easy. The Companion Animal Parasite Council reports that giardiasis is often misdiagnosed, because an affected animal sheds cysts intermittently, so sometimes there aren't any in a sample.
The CAPC recommends that cats showing symptoms of giardia have stool samples tested in several ways. These include the direct smear, in which a fresh fecal sample is examined under a microscope; fecal flotation using a centrifuge to mix the sample followed by a search for cysts under a microscope; and the enzyme-linked immunosorbent assay test.
Medicate and Sanitize to Treat
Vets typically prescribe metronidazole, marketed under the brand name Flagyl, to treat giardiasis in cat. This antibiotic isn't approved for treating giardiasis in cats by the U.S. Food and Drug Administration, but the FDA permits veterinarians to use it off-label.
You'll need to bathe your cat to get rid of cysts on his coat. If you can't do that yourself, take him to a groomer. If you have other felines living in your house, they also require medication and bathing, even if they are asymptomatic. Thoroughly disinfect your house, and consider replacing bedding, bowls and toys.