Cryptosporidium & Isospora in Dogs & People

This research summary was reviewed in February 2025 to confirm its continued clinical relevance.

In the Literature

Miller DL, Liggett A, Radi ZA, Branch LO. Gastrointestinal cryptosporidiosis in a puppy. Vet Parasitol. 2003;115(3):199-204. doi:10.1016/s0304-4017(03)00237-1

Summary

An 8-week-old Yorkshire terrier had a history of diarrhea, weakness, and isosporiasis. A necropsy was performed within 4 hours after death. Significant findings included a thymus that was one tenth the normal size and lymphoid depletion. Cryptosporidium organisms were found in the stomach crypts, gastric surface epithelium, and the villus border of the small intestine. The small intestine contained Isospora organisms at sexual and asexual stages. Cryptosporidium and Isospora species are primarily opportunistic organisms that may be life-threatening in individuals with compromised immune systems. The lymphoid depletion and thymic atrophy in this puppy suggest an underlying immunosuppressive factor, such as viral infection or malnutrition. The Cryptosporidium was identified with PCR and molecular analysis as Cryptosporidium canis. Although Cryptosporidium infections in dogs most often occur in the intestine, this case is different because of the invasion of the gastric region, which may have been due to displacement by the Isospora species or may represent systemic infection.

Commentary

Cryptosporidium is a worldwide pathogen that infects many different species, including humans. C canis and Cryptosporidium parvum are the only species that have been found in naturally infected dogs. C canis appears to be the only species that is clinically significant and it is not believed to be pathogenic to humans; however, any suspected case should be treated as a zoonotic risk.