ISSN 2398-2942      

Isospora ohioensis


David Lindsay




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

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Clinical Effects



  • Asexual stages and gametocytes are located in the epithelial cells of the posterior two-thirds of the small intestine of dogs. Subsequent asexual and sexual stages are found through the small intestine, but particularly in the ileum and in the cecum and colon. Here parasites occur mainly in the epithelial cells at the tips of the villi but also throughout the villus and in the crypts.
  • 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.
  • 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 lifecycle.

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.
  • Disease has been induced in one experiment.
  • Heavy infection caused hyperemia of the jejunum, increased mucus production, villous atrophy, cryptitis, flattening of epithelial cells and desquamation of the tips of the villi in the posterior small intestine, cecum and colon.
  • These will induce decreased absorption, loss of fluid and electrolytes.

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 so 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

  • Sulfadimethoxide 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 their proven efficacy against Isospora suis in pigs but have been used only in very few dogs.
  • Trimethoprim/sulfadiazine Trimethoprim (30-60 mg/kg in larger dogs, half this for dogs <4 kg, administered daily for 6 days). 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.
  • Remove feces frequently.
  • Wash pens well to remove oocysts via the drains.
  • Desiccation will kill oocysts over several days.
  • Ammonia disinfectants will be the most effective.


  • 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.
  • Dubey J P (1978) Life-cycle of Isospora ohioensis in dogs. Parasitology 77 (1), 1-11 PubMed.
  • Dubey J P (1978) Pathogenicity of Isospora ohioensis infection in dogs. JAVMA 173 (2), 192-197 PubMed.

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