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.



Cryptosporidium species

Cats with cryptosporidiosis have been documented worldwide.15,16 However, since genotyping was not performed in most of the studies, the specific prevalence of C. parvum, Cryptosporidium hominis, and C. felis in cats is not exactly known. The results of serologic and fecal testing in prevalence studies depend mainly on the study population and on the diagnostic test used.16

However, serum-antibody-based studies have shown that many cats are exposed. In one seroprevalence study in cats in the United States, about 8% of the cats had been exposed to a Cryptosporidium species.17 Cryptosporidium species oocysts or Cryptosporidium species antigen was detected in feces in 5.4% and 3.8% of the adults cats18 or kittens,19 respectively, in separate studies. When a polymerase chain reaction (PCR) assay was used to amplify Cryptosporidium species DNA in the feces of cats with diarrhea, 29.4% of the 180 cats tested had positive results.20

Giardia species

Giardia species infections in cats have also been reported around the world. And like cryptosporidiosis, reports of giardiasis prevalence rates have varied based on the population tested and the diagnostic test used. For example, in one study in adult cats in north-central Colorado, the prevalence of giardiasis was 3.9% and 1.9% in cats with and without diarrhea, respectively.18 In a study of kittens less than 1 year of age residing in New York state, Giardia species was detected in 6.1% and 8.1% of client-owned and shelter cats, respectively.19

Tritrichomonas foetus

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The worldwide prevalence rate of T. foetus infection in cats is unknown. Infections appear to be most common in cats in crowded environments; infection in feral cats and healthy cats is uncommon. In one study in cats at an international cat show, 31% of 117 cats owned by 89 different breeders were infected.21


Cryptosporidium species, Giardia species, and T. foetus can be transmitted by ingesting feces from mutual grooming or shared litter boxes. For Giardia and Cryptosporidium species, ingestion of contaminated food or water and contact with other infected animals (i.e. ingestion of prey species) is also likely to be associated with transmission.22 Although infection in cats with these agents is common, many infected cats have no clinical signs. Diarrhea is generally more common in young animals.9,23,24 Coinfection with more than one agent has also been reported.


Cryptosporidium species

When it occurs, diarrhea caused by cryptosporidiosis is associated with impaired intestinal absorption and enhanced anion secretion.25,26 Histologic examination of small-intestinal lesions from infected cats reveals loss of microvilli, degeneration of host epithelial cells, and atrophy of the villi.27 In some naturally infected cats, mild to moderate lymphocytic-plasmacytic duodenitis has been detected; however, it is unknown whether the inflammation was preexisting or from Cryptosporidium infection.27-29 Mononuclear cell infiltrates in the duodenum are common in AIDS patients with cryptosporidiosis, and as in some cats, the infiltrates resolve in some patients after treatment, suggesting the organism was the cause of the inflammation.30

It is not known why some cats and not others develop clinical signs of disease. The development of clinical signs might depend on various factors including the presence of immunodeficiency, coinfections, other gastrointestinal diseases, host susceptibility, or infection with more-pathogenic strains.


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