Types and incidence of parasitism varies with geographic regions. This article concerns itself with canine GI parasites of North America. Most parasites are diagnosed by a microscopic fecal examination using various chemicals to help concentrate the population of parasite eggs. Some parasites are visible to the naked eye although, they are not consistently shed into the feces. Eimeria and Isospora are the two most common coccidia of the dog.
Infection occurs upon ingestion of contaminated feces or food.
Upon ingestion, the parasite colonizes the lining of the small intestine and reproduction begins. As reproduction progresses the new coccidia are shed through the feces to the environment. Shedding of the protozoan can be asymptomatic or associated with signs of diarrhea and bloody stools. Puppies are most commonly affected. Most infections are not apparent and resolve on their own by self immunization.