Cystoisospora Infection In Humans, Dogs and Cats

Cystoisospora is a genus of coccidia, the large, spore-forming, single-celled obligate intracellular parasites. As obligate intracellular parasites, they must live and reproduce within an animal cell. Cystoisospora is found worldwide, especially in warm climates. In developed countries, it is found in recent immigrants, travelers returning from endemic regions, patients with AIDS and native populations in the United States. The disease is usually mild and occurs through contaminated food and water. A direct person-to-person transmission is unlikely.

Source: Case Rep Infect Dis. 2012; 2012: 640104.

In humans, the intestinal disease is caused by Cystoisospora belli (Isospora belli). The coccidian parasite infects the epithelial cells of the small intestine. The immature form of the parasite known as "oocytes" are ingested with water and food and then need to mature in the human gut to become infective. After completing its life cycle in the human body, newly formed oocytes are eliminated with the stool. Contaminated vegetables and raw food are a source for this infection. The resulting nonbloody diarrhea with crampy abdominal pain can last for weeks and is characterized by malabsoption, fever, nausea, vomiting, and weight loss. In infants and children the diarrhea can be severe. Infection is almost indistinguishable from cryptosporidiosis. Patients who are treated ususally improve in 7–10-days.

In dogs, the common species causing coccidiosis are Cystoisospora canis, Cystoisospora ohioensis and Cystoisospora burrowsi. About 4 percent of dogs in the United States are infected with Cystoisospora canis. The most common sign of infection in puppies is copious and watery diarrhea that may persist for weeks.

Cats are infected with Cystoisospora felis and ususlly exhibit weakness, weight loss, dehydration and diarrhea with blood and mucus. Kittens and otherwise weakened animals have more severe symptoms. Older and generally healthy cats may have no symptoms at all.


  1. Georgis' Parasitology for Veterinarians. Dwight D. Bowman
  2. Encyclopedia of Food Safety
  3. The Cat Breeders Handbook
  4. Severe Isospora (Cystoisospora) belli Diarrhea Preceding the Diagnosis of Human T-Cell-Leukemia-Virus-1-Associated T-Cell Lymphoma
  5. Enteric Protozoa in the Developed World: a Public Health Perspective



Home Contact RSS