Coccidia are microscopic parasites that commonly infect the intestines of dogs and cats.  Isospora canis and Isospora felis are the forms of the parasite that most often infect dogs and cats.  However, Cryptosporidium and Toxoplasma are other forms of coccidia that may also infect dogs, cats, other animals and even people.
 
Coccidiosis rarely affects a healthy dog or cat significantly, but it can lead to gastrointestinal problems. Puppies and kittens are more at risk for serious infection.  Clinical signs can include watery diarrhea, weight loss, dehydration, decreased or absent appetite, vomiting, abdominal pain, anemia, mental depression, and rarely death. Transmission of coccidia begins when the immature coccidia, or oocysts, are passed in the feces from an infected dog or cat into the environment, where they mature and can be ingested by another animal. Transmission also can occur when a dog or cat eats an animal such as a rodent that has been infected with the Isospora parasite.

To diagnose coccidiosis, your veterinarian or veterinary technician will perform a fecal flotation in which a stool sample is evaluated under a microscope for the presence of parasites. Coccidia may be difficult to detect because these parasites are very small compared to the eggs passed from intestinal worms such as roundworms.  

Treatment involves the use of drugs called sulfonamides, which are antibiotics that decrease the numbers of coccidia. This medication is given for 10 to 14 days after which a stool sample is checked.  Occasionally, a second course of antibiotics is required.  The key to prevention is proper sanitation to ensure that the environment is free of feces. Once the Isospora are passed in the feces, they can quickly develop into the infective stage, so rapid removal of the feces is very important. Mature oocysts of Isospora are resistant to most cleaning products and can survive for months to years in the environment. However, the use of strong ammonia-containing compounds and steam cleaning kills the infectious oocysts.  In addition, dogs and cats should not be permitted to ingest rodents, since rodents may be carriers of the parasites.