Coccidia (Isospora) in Cats and Dogs

Coccidia (Isospora) in Cats and Dogs

Animals Affected

Puppies and kittens. Rarely, adult cats and dogs.


Coccidia are microscopic intestinal parasites of dogs and cats.   They are extremely common, but they very rarely cause symptoms in adult animals.   In puppies and kittens, they are a frequent cause of diarrhea.

Untreated, severe cases of coccidia in young animals can lead to profuse diarrhea, dehydration, and serious illness.  However, most cases of coccidia do not have these consequences.

Treatment of coccidia can be frustrating.  Some pets require a prolonged period of treatment to eliminate the parasites.  However, once treatment is implemented, the serious complications of coccidia are unlikely to develop.

The scientific name of the type of coccidia discussed in this article is Isospora. Other types of coccidia exist.  The other types of coccidia have unique clinical features.   This article is intended to discuss only Isospora.


  • Diarrhea is the most common symptom of coccidia infestation.  The degree of diarrhea varies.  Some pets may have slightly loose bowel movements.  Others may have severe, malodorous diarrhea.  In some cases the diarrhea will be bloody.
  • Some pets with coccidia infestations show no symptoms.

Risk Factors and Prevention

  • Age is the primary risk factor.  Coccidia infestations occur mostly in puppies and kittens.  Healthy adult animals generally will not be affected.
  • Coccidia is contracted by exposure to the organism in the environment.  Hygiene plays a role in the development of infestation.  However, the organisms are extremely common.  Infestations can develop even in very clean environments.
  • Individual pets have unique susceptibilities to coccidia.
  • Stress or decreased immune system function may contribute to a pet’s susceptibility.  Kittens infected with FIV or feline leukemia may be at increased risk.
  • Recently adopted puppies and kittens are most likely to suffer from coccidia infestations.


Severe diarrhea from coccidia infestations can lead to dehydration, failure to grow, or death. These complications are unlikely to develop in animals that receive treatment for coccidia.

Coccidia can exacerbate diarrhea caused by roundworms or intestinal disease.

Pets with diarrhea due to coccidia are more likely to defecate in inappropriate locations.


Coccidia infestation is diagnosed through microscopic observation of the organisms in specially prepared samples of feces.  This method is not 100% accurate.

In many cases, a presumptive diagnosis of coccidia is made based on age and symptoms. These pets may be treated for coccidia and monitored for resolution of diarrhea.


Sulfadimethoxine (Albon®) is most commonly used to treat coccidia.  The medicine is given orally for 3 – 21 days.   In many cases pets require more than one treatment cycle to eliminate the parasite.

Ponazuril is a medication that recently has been shown to be highly effective in treating coccidia.  Many experts now agree that Ponazuril is more effective than, and superior to sulfadimethoxine.


Diarrhea should begin to resolve within a few days of starting treatment.

After treatment, follow-up fecal tests should be run to ensure that the parasite is no longer present in large numbers.


Coccidia can spread from one pet to another.  However, healthy adult pets are very unlikely to contract the parasite.  Because of this, it is uncommon for newly adopted puppies or kittens to spread the disease to established adult animals in the house.

Copyright © Eric Barchas, DVM All rights reserved.
The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.