Protozoan Diseases in Dogs

Protozoa are one-celled animals that are not visible to the naked eye, but are visible under the microscope. They are usually carried in water. A fresh stool specimen from the infested animals, dog in our case,  is required to identify the adult parasite or its cysts, the dormant stage.


Dogs and most of the herbivores (cattle, sheep, goats, water buffalo & horses) are hosts to Neosporum caninum, with cattle as the intermediate host. Some wild and captive animals (e.g. deer, rhinoceros, rodents, rabbits, coyotes, wolves, foxes) can also get infected. Dogs initially acquire the infection by eating infected meat, but once infected, a pregnant bitch can pass infection on through the placenta to all of her unborn puppies. They also shed oocysts of N. caninum in feces.

Dogs will show nerve and muscle problems, possibly even leading to paralysis/paresis. Pneumonia, heart problems, and skin problems may also be seen. It may also cause abortion in late gestation. Infected litters or individual new born puppies may develop progressive hind-limb paresis associated with polyradiculoneuritis, myositis, and muscle atrophy.

Diagnosis of Canine Neosporosis

Clinically affected dogs often have Neospora antibody levels much higher than levels seen in subclinically infected individuals. Biopsy of clinically affected tissues demonstrates nonsuppurative inflammation and may reveal the presence of protozoal organisms. Immunohistochemistry or PCR may be required to detect the organisms or to differentiate them from other protozoa.

Dogs with symptomatic neosporosis usually do not shed oocysts in feces. The finding of Neospora in routine fecal floats is luck, because of the reason that dogs typically shed oocysts for only a period of days or weeks after ingesting tissue of an infected animal.

The tiny oocysts are round to slightly oval and 10–11 microns in diameter; in comparison, Giardia cysts are oblong and approximately 9 × 13 microns, and coccidia are 2–4 times the diameter of Neospora. A smooth outer contour helps to differentiate Neospora oocysts from pitted pollen grains of similar size.


Clindamycin, pyrimethamine (Fansidar), and sulfadiazine are mostly used in treatment.

The prognosis is negatively associated with the severity of presenting clinical signs and with delayed treatment. The prognosis is poor in puppies if disease has progressed to hind-limb paresis with atrophied, rigid limbs.


Dogs should not be fed raw or uncooked meat, especially beef. Dogs should also be prevented from defecating in cattle yards and pastures to help prevent exposure. Some veterinarians will attempt treating subsequent litters of affected bitches in-utero, as it is expected all future puppies will be infected. This must begin after at least two weeks into the pregnancy, to avoid damage to the developing embryos.