An update on three important protozoan parasitic infections in cats: cryptosporidiosis, giardiasis, and tritrichomoniasis - Veterinary Medicine
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An update on three important protozoan parasitic infections in cats: cryptosporidiosis, giardiasis, and tritrichomoniasis
Our knowledge of these protozoan parasites in cats continues to expand. Here's what you need to know about diagnosing these infections and treating affected patients.



Because Cryptosporidium species, Giardia species, and T. foetus have been detected in the feces of cats with and without diarrhea, a positive test result does not always prove the agent is the cause of diarrhea. If the diagnostic workup does not reveal another cause of diarrhea, initiate treatment. Like bacteria, protozoans can have variable responses to different drugs. So be prepared to try an alternate drug if a cat's clinical signs don't resolve.

Cryptosporidium species

More than 100 compounds have been evaluated to treat cryptosporidiosis in laboratory animal models, people, and cattle, but no treatment has consistently eliminated clinical signs or the organism from the gastrointestinal tract. Few studies have described the treatment of feline cryptosporidiosis, and to our knowledge, none have been controlled.


In one case report, clindamycin hydrochloride (25 mg/kg orally daily) was administered to a cat with chronic cryptosporidiosis and lymphocytic duodenitis.28 After 60 days of therapy, there was no further improvement in stool consistency, and oocysts were still detected. So clindamycin was discontinued on Day 60, and tylosin was administered (11 mg/kg orally twice daily) for 28 days. Stools were normal within seven days after tylosin therapy was initiated, and the fecal samples assessed for oocysts during the treatment were negative. The results from eight fecal examinations were negative for oocysts six months after the completion of tylosin therapy. The inflammatory changes in the bowel resolved after treatment, suggesting the inflammation was from Cryptosporidium species infection.

We have treated many cats with presumed cryptosporidiosis with tylosin at a dosage of 10 to 15 mg/kg given orally twice daily for 21 days, and diarrhea has resolved in about 50% of the cases (Lappin MR, Scorza AV, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colo: Unpublished data, 2006). However, these observations are uncontrolled, and the signs in the affected cats may have resolved spontaneously. It is also possible the anti-inflammatory or antibacterial effects of tylosin played a role in clinical responses. In addition, tylosin is not tolerated by most cats because of its unpleasant taste.


Azithromycin has been evaluated in animal models of infection and in people that have cryptosporidiosis with some encouraging preliminary results.52 Azithromycin achieves high biliary concentrations. In a recent study, administering azithromycin to dairy cows infected with Cryptosporidium species significantly reduced oocyst shedding and improved clinical signs of diarrhea.53 We currently recommend azithromycin at a dosage of 10 mg/kg given orally daily in cats that are intolerant or nonresponsive to tylosin. The optimal duration of therapy is unknown but is usually several weeks. Other than the potential for mild gastrointestinal side effects, the drug appears safe for use in cats.


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