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Toxoplasmosis in Dogs

By Otto M. Radostits, CM, DVM, MSc, DACVIM (Deceased), Professor Emeritus, Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan ; David A. Ashford, DVM, MPH, DSc, Assistant Area Director, International Services, APHIS, USDA ; Craig E. Greene, DVM, MS, Professor, Department of Small Animal Medicine, College of Veterinary Medicine, University of Georgia ; Eugene D. Janzen, DVM, MVS, Professor, Production Animal Health, Faculty of Veterinary Medicine, University of Calgary ; Bert E. Stromberg, PhD, Professor, Veterinary and Biomedical Sciences, College of Veterinary Medicine, University of Minnesota ; Max J. Appel, DMV, PhD, Professor Emeritus ; Stephen C. Barr, BVSc, MVS, PhD, DACVIM, Professor of Medicine, Department of Clinical Sciences, College of Veterinary Medicine, Cornell University ; J. P. Dubey, MVSc, PhD, Microbiologist, Animal Parasitic Diseases Laboratory, Beltsville Agricultural Research Center, USDA ; Paul Ettestad, DVM, MS, State Public Health Veterinarian, Epidemiology and Response Division, New Mexico Department of Health ; Kenneth R. Harkin, DVM, DACVIM, Associate Professor, College of Veterinary Medicine, Kansas State University ; Delores E. Hill, PhD, Parasitologist, U.S. Department of Agriculture ; Johnny D. Hoskins, DVM, PhD, Small Animal Consultant ; Jodie Low Choy, BVSc, BVMS, IVAS Cert, Menzies School of Health Research; University Avenue Veterinary Hospital, Northern Territory, Australia ; Barton W. Rohrbach, VMD, MPH, DACVPM, Associate Professor, Department of Comparative Medicine, Veterinary Teaching Hospital, University of Tennessee ; J. Glenn Songer, PhD, Professor, Department of Veterinary Science and Microbiology, University of Arizona ; Joseph Taboada, DVM, DACVIM, Professor and Associate Dean, Office of Student and Academic Affairs, School of Veterinary Medicine, Louisiana State University ; Charles O. Thoen, DVM, PhD, Professor, Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine, Iowa State University ; John F. Timoney, MVB, PhD, Dsc, MRCVS, Keeneland Chair of Infectious Diseases, Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky ; Ian Tizard, BVMS, PhD, DACVM, University Distinguished Professor of Immunology; Director, Richard M. Schubot Exotic Bird Health Center, Department of Veterinary Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University

Also see professional content regarding toxoplasmosis.

Toxoplasmosis is caused by Toxoplasma gondii, a protozoan parasite that infects humans and other warmblooded animals. It is found worldwide.

Felines (members of the cat family) are the only definitive hosts of the parasite. Both wild and domestic cats serve as the main reservoir of infection. In dogs, a generalized infection may occur as the parasites travel through the body and invade the tissues.

Adult animals with vigorous immune systems control the spread of the parasite efficiently; therefore, toxoplasmosis usually causes no signs in healthy dogs. However, in puppies, the parasites may spread throughout the body. Signs of infection include fever, diarrhea, cough, difficulty breathing, jaundice, seizures, and death. Adult animals with weakened immune systems are extremely susceptible to developing sudden, generalized toxoplasmosis.

In many cases, treatment is not necessary. If warranted, your veterinarian will prescribe antibiotics to treat toxoplasmosis. Anticonvulsant medications may be used to control seizures. Fluids or other medication given by intravenous injection may be necessary for animals that are dehydrated or severely debilitated due to the infection.

Transmission of toxoplasmosis to people is an important problem. In some areas of the world, as much as 60% of the human population has antibodies to the organism and are likely to be persistently infected. Toxoplasmosis is a major concern for people with weakened immune systems. In these individuals, toxoplasmosis usually affects the nervous system and results from the emergence of T gondii from tissue cysts located in the brain as immunity wanes rather than from primary T gondii infection. Toxoplasmosis is also a concern for pregnant women because the organism can migrate across the placenta and cause birth defects. Infection may occur after eating undercooked meat or accidental consumption of cysts from cat feces. To prevent infection, people handling meat should wash their hands thoroughly with soap and water after contact, and also thoroughly wash all cutting boards, sink tops, knives, and other materials. The organism present in meat is killed by contact with soap and water. They can also be killed by exposure to extreme cold or heat. Tissue cysts in meat are killed by heating the meat throughout to 67°C (152.6°F) or by cooling to −13°C (8.6°F). Toxoplasma in tissue cysts are also killed by exposure to gamma irradiation. Meat of any animal should be cooked to 67°C (152.6°F) before consumption, and tasting meat while cooking or while seasoning should be avoided. Pregnant women should avoid contact with cat litter, soil, and raw meat. Pet cats should be fed only dry, canned, or cooked food. The cat litter box should be emptied daily, preferably not by a pregnant woman. Gloves should be worn while gardening. Vegetables should be washed thoroughly before eating, because they may have been contaminated with cat feces.