Cryptosporidium Infection

Cryptosproidium is a protozoal parasite which causes cryptosproidiosis, an important zoonotic disease recognized in the early 1980s. Early studies assumed that all infections in mammals, including humans, were caused by the parasite Cryptosporidium parrum. Recent studies using molecular biologic tools and host-specificity studies indicate that cats and dogs have their own unique species of Cryptosporidium (C. felis and C. canis, respectively). Initial studies indicate that owning a cat or dog does not increase the risk of humans acquiring cryptosporidiosis, although human infections with C. felis and C. canis have been found in patients with AIDS, immunosuppressed patients, and children from impoverished areas. Current guidelines from the US Public Heath Service and Infectious Diseases Society of America recommend that HIV-infected humans should not take into their homes stray dogs or cats, animals with diarrhea, or dogs and cats younger than 6 months of age. They further recommend that if a dog or cat younger than 6 months of age is acquired by an HIV infected person, the animal should be tested for Cryptosporidium. C. canis is a Cryptosporidium species of public health significance, and under favorable conditions, the transmission of the parasite from dogs to humans may occur. Surveys indicate that up to 38 percent of cats and up to 44 percent of dogs are infected with Cryptosporidium species. C. parrum have been responsible for drinking water associated outbreaks of human cryptosporidiosis. Human-to-human transmission also occurs.3

Important Food- And Waterborne Pathogen

Cryptosporidia develop in the epithelial cells in the digestive, respiratory, and urinary tracts of animals and cause reduced uptake of fluids, electrolyte and nutrients from the gut. Clinical signs of cryptosporidiosis in cats and dogs vary from none to chronic or intermittent diarrhea. Fluids and other supportive measures should be used in animals with diarrhea, but there is no proven safe and effective treatment of cryptosporidiosis. Cryptosporidia oocysts are very resistant to environmental damage, chlorination, and standard cleansers. This makes Cryptosporidium species an important food- and waterborne pathogen. Extreme temperatures and prolonged contact with ammonia destroy the oocysts.


The small size of Cryptosporidium oocysts makes them difficult to detect. Oocysts are often overlooked unless an examiner is specifically looking for them. Fecal flotation techniques used routinely in veterinary laboratories are adequate to demonstrate Cryptosporidium oocysts if large numbers are present.

No drug has been proven effective in eliminating the organism from the gastrointestinal tract. However, administration of several different drugs, such as tylosin, azithromycin, paramomycin, has been effective in the control of clinical signs in dogs and cats. Some animals may require treatment with antimicrobials for weeks to achieve maximum effect.3


  1. Cryptosporidium infection in cats and dogs (
  2. Possible Transmission of Cryptosporidium canis among Children and a Dog in a Household Lihua Xiao, Vitaliano A. Cama, Lilia Cabrera, Ynes Ortega, Julie Pearson, and Robert H. Gilman
  3. Lila Miller, Kate Hurley (editors). Infectious Disease Management in Animal Shelters

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