Primer On Coccidia Infection

Written and reviewed by John A. Bukowski, DVM, MPH, PhD
and Susan E. Aiello, DVM, ELS 

Coccidiosis is an infection of the intestinal tract in dogs and cats that's caused by coccidia, which are single-celled parasites.  

The immature forms of coccidia are called oocysts, and they are passed in the feces of infected dogs or cats. The oocysts then develop through a process called sporulation and become infectious after they have matured. 

Coccidia. Image Utah State University

How are coccidia different from other intestinal parasites?

Intestinal parasites such as worms are complex organisms that live largely within the open tube of the digestive tract.  Coccidia are single-celled organisms that live and reproduce within the walls of the digestive tract.

Dogs and cats become infected directly by swallowing oocysts that have sporulated and matured, or by eating the feces or intestines of infected wildlife such as rodents.  

Pet stores, boarding kennels, and other areas that may have large amounts of fecal contamination are common areas for coccidiosis.

Most dogs and cats infected with coccidia do not show any signs.  

However, puppies, kittens, and older pets can become sick from infection because of weak immune systems.  Diarrhea is the most common sign.  Vomiting is rare.

Coccidiosis is diagnosed by identifying the oocysts on a microscopic examination of a fecal sample.  

Infected pets are treated with a sulfa-type antibiotic.  Re-infection is common, and disinfection of the environment is important for control.

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