ISSN 2398-2942      

Isospora canis


Peter Irwin

David Lindsay

Synonym(s): I. canis




  • Phylum: Apicomplexa.
  • Class: Sporozoasida.
  • Family: Eimeriidae.
  • Genus: Isospora.
  • Species: canis.

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Clinical Effects



  • Schizonts and gametocytes are located in a subepithelial position in the distal third of the villi in the posterior third of the small intestine of dogs.
  • Cystozoites occur in the parenteral tissues, probably the mesenteric lymph nodes and the abdominal viscera, of rats, mice, probably other herbivores and also the tissues of the dog.


  • Intestinal development Isospora oocysts.
  • Oocysts.
  • Cystozoites in paratenic herbivorous hosts.
  • Cystozoites in tissues of dog from where reactivation and renewed intestinal infection is a likely scenario.


Direct lifecycle

  • Feco-oral transmission in kennel situations.
  • Development of the oocysts is very rapid, the prepatent period of infection is short and, as the biotic potential of Isospora is high, very large numbers of oocysts can build up rapidly to pathogenic levels.

Indirect lifecycle

  • Infection is derived by ingestion of cystozoites in the tissues of prey.
  • Numbers are unlikely to be sufficient to cause disease but this source of infection could maintain the life cycle.

Reactivation of cystozoites in the dog

  • The presence of heavily infected animals continues to suggest that reactivation of cystozoites in immunosuppressed or stressed puppies may then initiate intestinal multiplication and so could be an important factor in causing disease.

Pathological effects

  • Some protective immunity and decreased susceptibility to infection with age does seem to occur in regard to the intestinal stages.
  • Disease is seen most commonly in puppies that are a few weeks to a few months old, that are in kennels and/or in association with stress, eg weaning, with or without transport and change in diet, or immunosuppression.
  • Up to 5% of dogs are infected with Isospora spp. More common in young dogs.
  • Remains controversial but high oocyst counts have been associated with poor weight gain and bloody diarrhea, particularly in young puppies that have been stressed at weaning and by transport.
  • The site of the intestinal stages in a subepithelial location of villi in the posterior portion of the small intestine does suggest that I. canis is pathogenic.
  • Heavy infection will cause villous atrophy, increased mucus production, decreased absorption, loss of fluid and electrolytes, and hemorrhage where the organisms are rupturing from their subepithelial position.

Other Host Effects

  • Obligate, intracellular parasite lying within a parasitophorous vacuole.


Control via animal

  • In view of the controversy surrounding the pathogenicity of Isospora spp, concurrent exacerbating infections should be sought and treated and any sources of stress corrected.
  • Remove animal from surroundings and, therefore, from source of infection.
  • There is no clear evidence that common anticoccidials have real efficacy, but they may shorten the course of the disease and, therefore, should be administered in conjunction with supportive therapy (fluids, nursing as required).

Control via chemotherapies

  • Sulfamethoxine is approved in the US for the treatment of coccidiosis in dogs. No products are licensed in the UK.
  • Toltrazuril Toltrazuril and diclazuril seem the most likely candidates with proven efficacy against Isospora suis in pigs, but they have been used only in very few dogs.
  • Trimethoprim/sulfadiazine (30-60 mg/kg in larger dogs, half this for dogs <4 kg, administered daily for 6 days) Trimethoprim. Some toxicity has been reported.

Control via environment

  • The oocysts sporulate very rapidly and are very resistant.
  • Parasite control can be difficult due to the presence of both oocyst and rodent sources of infection, and the rapid multiplication of the parasite.
  • Attention to hygiene (remove feces frequently).
  • Good hygiene specially where many pups congregate (ie breeding kennels, pet shops).
  • Avoid contamination of food with feces.
  • Disinfect cages, runs and feed bowls by immersion in boiling water, or use of 10% ammonia solution.


  • None.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Lindsay D S, Dubey J P, Blagburn B L (1997) Biology of Isospora spp. from humans, nonhuman primates and domestic animals. Clin Microbiol Rev 10 (1), 19-34 PubMed.
  • Lepp D L & Todd K S Jr. (1974) Lifecycle of Isospora canis Nemseri, 1959 in the dog. J Protozol 21 (2), 199-206 PubMed.

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