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.



Paromomycin is an aminoglycoside antibiotic that is poorly absorbed from the normal gastrointestinal tract. The efficacy of the drug in people that have AIDS and cryptosporidiosis is controversial. However, in clinical practice, paromomycin is commonly used to treat cryptosporidiosis in patients with HIV infection.54 Paromomycin was effective in clearing Cryptosporidium species oocysts from the feces of a naturally infected cat with persistent diarrhea55 and from the feces of eight experimentally inoculated cats (McReynolds C, McReynolds LM, Brewer MM, et al. Master's defense, Colorado State University, Fort Collins, Colo: Unpublished data, 2006). However, the diagnostic tests used in the follow-up period in both studies may not have been sensitive enough to detect animals in a carrier state.

We have recently studied groups of presumably immunocompetent kittens and adult cats that were infected with both Giardia and Cryptosporidium species (Scorza AV, Lappin MR, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colo: Unpublished data, 2006). Cats with coinfections seem to be more difficult to treat than cats infected with either organism alone. Recently, we used paromomycin at a dosage of 150 mg/kg given orally daily to control diarrhea in two cats with resistant Giardia species and C. felis infection that had not responded to treatment with other drugs. However, treatment was needed for more than 21 days to achieve maximal clinical response and stop fecal shedding.

Paromomycin should be considered a rescue drug (to be used only in resistant infections) and should never be used in cats with bloody diarrhea because of the risk of systemic absorption and induction of renal disease or deafness. In one study of cats with Tritrichomonas species infection treated with paromomycin (125 to 165 mg/kg orally every 12 hours for five days), four out of 32 cats developed acute renal failure, and three of the four cats became deaf.56


In people, one of the most promising agents used to treat cryptosporidiosis is nitazoxanide, a derivative of nitrothiazole, which is effective against a broad spectrum of parasites and bacteria. To date, nitazoxanide is the only drug approved by the FDA to treat diarrhea caused by Cryptosporidium and Giardia species in children.57,58 We are currently evaluating nitazoxanide to treat a number of small-animal parasites. Some of the dogs and cats with Cryptosporidium or Giardia species infections have had diarrhea resolve after the administration of nitazoxanide at a dosage of 25 mg/kg given orally every 12 hours for at least five days, but it is too early to suggest the efficacy of this treatment.

Giardia species

Because of the potential for zoonotic transmission, the treatment of cats with giardiasis may be advocated whether or not they are clinically ill. In human medicine, a combination of nutritional intervention and phytotherapy is the first line of approach for treating giardiasis because the infections are often self-limiting and drug therapy likely does not eliminate infection. Antibiotic treatment is often reserved for cases in which the nutritional approach has been ineffective.

Nutritional intervention

Nutritional management is based on foods and supplements that inhibit Giardia species growth, replication, or attachment to the enterocytes and that promote host immune defense against the parasite. Consuming a whole-food, high-fiber, low-simple-carbohydrate, low-fat diet will help reduce the acute signs of giardiasis in people.59 Probiotics, wheat germ, and medicinal herbs including garlic and flavonoid-containing herbs have been reported to have anti-Giardia species properties.59 However, the efficacy of these approaches for treating giardiasis in cats is unknown. We generally use highly digestible bland diets if vomiting and small bowel diarrhea are the main clinical signs. If large bowel diarrhea is the principal clinical sign, high-fiber diets are used.


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