Canine Coccidia

(Cystoisospora spp. [syn. Isospora spp.])

Cystoisospora spp. (Isospora spp.) are apicomplexan protozoa transmitted directly by the faecal-oral route, especially in unhygienic, overcrowded environments. Species harbored by dogs are highly host-specific and a frequent cause of diarrhoea in puppies.

Parasite: Cystoisospora canis, Cystoisospora ohioensis, Cystoisospora burrowsi and Cystoisospora neorivolta
Common name: Canine coccidian (syn. Isospora)
Host: dogs
Pre-patent period: 5-13 days
Location of adults: small intestine
Distribution: worldwide
Transmission route: ingestion of sporulated oocysts
Zoonotic: No



Clinical signs

Cystoisospora is most commonly seen in puppies. Common clinical signs include anorexia, vomiting, watery (rarely hemorrhagic) diarrhoea, dehydration and weight loss. Most dogs will develop a strong acquired immunity to infection, shedding only low intensities of oocysts as asymptomatic adults.


Clinical signs may precede oocyst shedding and in this case, diagnosis has to be based on history and clinical signs. Oocysts isolated on standard faecal flotation (S.G. 1.20)(SOP 1), are unsporulated (Fig 1) and develop to infective forms (sporulate) in 2-3 days (Fig 2). Each sporulated oocyst contains two sprorocysts with four sporozoites each. Oocysts of C. canis measure 38 × 30 μm, whereas those of the C. ohioensis complex, which includes C. burrowsi and C. neorivolta measure 25 × 20 μm. Care should be taken to differentiate oocysts from those of Eimeria spp. (Fig 3) that may be mechanically ingested through coprophagy.

Figure 1. Unsporulated oocyst of Cystisospora canis on faecal flotation. (Image credit: The University of Melbourne parasite image library.)
Figure 2. After incubation, oocysts of Cystisospora spp. sporulate to contain two sprocysts, each with four sporozoites. (Image credit: University of Melbourne parasite image library.)
Figure 3. Following incubation, oocysts of Eimeria spp. sporulate to contain four sprocysts, each with two sporozoites. (Image credit: University of Melbourne parasite image library.)


Treat affected animals with oral sulfadimethoxine at 50 mg/kg daily for 5 – 20 days or oral trimethoprim-sulfonamide at 15-30 mg/kg for animals less than 4 kg and 30-60 mg/kg for animals more than 4 kg, for a period of 6 days. Alternatively, a single dose of oral toltrazuril at 10 mg/kg or oral ponazuril at 50 mg/kg daily for 3 days can be used. If clinical signs persist, re-testing and re-treatment may be necessary.


Pregnant females should be treated (as above) and bathed before whelping to remove sporulated oocysts on their hair coat. Ammonia-based disinfectants should be used for de-contamination of premises. For further control options refer to the General Considerations and Recommendations section.

Public health considerations