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Protozoan Diseases in Dogs

Protozoa are one-celled animals that are not visible to the naked eye, but are easily seen under the microscope. They are usually carried in water. A fresh stool specimen is required to identify the adult parasite or its cysts (called oocysts).


This disease is caused by a protozoan that infects warm-blooded animals. Cats are the definitive host, but other animals, including dogs and humans, can act as intermediate hosts. It is not common in dogs. The principal mode of transmission in dogs and people raw or undercooked pork, beef, mutton, or veal that contains the organism Toxoplasma gondii.

Oocysts excreted in the stools of infected cats, or ingesting spores, are other potential sources of infection. Oocysts require one to three days under ideal conditions of warm temperature and high humidity to produce spores. These infective spores can survive in the environment for months or years. Only cats excrete the oocytes in their stool. The dog is therefore not capable of infecting other dogs and humans in this way.

Most dogs with toxoplasmosis experience no symptoms. When symptoms do occur, they include fever, loss of appetite, lethargy, cough, and rapid breathing. Other signs are weight loss, diarrhea, lymph node enlargement, and swelling of the abdomen. Young puppies with toxoplasmosis may show signs of pneumonia, hepatitis, or encephalitis. In brood bitches, intrauterine infection can result in abortion, stillbirths, and the birth of sick puppies who die within the first week of life.

The diagnosis is made by serology. An elevated IgM titer (by ELISA tests) is diagnostic for active or recent infection.

Treatment: Antibiotics are available to treat acute toxoplasmosis. Clindamycin is the drug of choice.

Prevention: Prevent the disease by keeping your pet from roaming and hunting. Cook all fresh meat (both yours and your pets’) to a temperature of at least 150°F (65.5°C). Wash your hands with soap and water after handling raw meat. Always clean kitchen surfaces that come in contact with raw meat.


This disease is caused by a species of coccidia commonly found in the feces of puppies and, occasionally, adult dogs. The main sign is diarrhea. Because infection is mild, symptoms usually do not occur unless the pup’s resistance has been lowered by a concurrent disease, malnutrition, or immunosuppression.

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