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Toxoplasmosis in Cats

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 ; Max J. Appel, DMV, PhD, Professor Emeritus ; David A. Ashford, DVM, MPH, DSc, Assistant Area Director, International Services, APHIS, USDA ; 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 ; Craig E. Greene, DVM, MS, Professor, Department of Small Animal Medicine, College of Veterinary Medicine, University of Georgia ; Delores E. Hill, PhD, Parasitologist, U.S. Department of Agriculture ; Johnny D. Hoskins, DVM, PhD, Small Animal Consultant ; Eugene D. Janzen, DVM, MVS, Professor, Production Animal Health, Faculty of Veterinary Medicine, University of Calgary ; Jodie Low Choy, BVSc, BVMS, IVAS Cert, Menzies School of Health Research; University Avenue Veterinary Hospital, Northern Territory, Australia ; Dennis W. Macy, MS, DACVIM, Professor of Medicine and Oncology, College of Veterinary Medicine and Biomedical Sciences,Colorado State University ; Dudley L. McCaw, DVM, DACVIM (Small Animal, Oncology), Professor, Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University ; 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 ; Richard A. Squires, BVSc (Hons), PhD, DVR, DACVIM, DECVIM-CA, GCertEd, MRCVS, Head of Veterinary Clinical Sciences, School of Veterinary and Biomedical Sciences, James Cook University ; Bert E. Stromberg, PhD, Professor, Veterinary and Biomedical Sciences, College of Veterinary Medicine, University of Minnesota ; 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 warm-blooded animals. It has been found worldwide. Wild and domestic felines (members of the cat family) are the only definitive hosts of the parasite. Infected cats can transmit the disease to humans and other animals.

There are 3 infectious stages of Toxoplasma gondii: tachyzoites (rapidly multiplying form), bradyzoites (tissue cyst form), and sporozoites (in oocysts). The parasite is transmitted by consumption of infectious oocysts in cat feces, consumption of tissue cysts in infected meat, and by transfer of tachyzoites from mother to fetus through the placenta. Cats generally develop immunity after the initial infection; therefore, they shed oocysts only once in their lifetime (from approximately 3 days after infection and for about 20 days thereafter).

The tachyzoite is the stage responsible for tissue damage. Therefore, signs depend on the number of tachyzoites released, the ability of the infected cat’s immune system to limit tachyzoite spread, and the organs damaged by the tachyzoites. Because adult animals with normally functioning immune systems control tachyzoite spread efficiently, cats with toxoplasmosis usually have no signs of illness. However, in kittens tachyzoites spread throughout the body. The signs include fever, diarrhea, cough, difficulty breathing, jaundice, seizures, and death.

In many cases, treatment is not necessary in infected cats. If warranted, your veterinarian will prescribe antibiotics to treat toxoplasmosis. Anticonvulsant medications may be used to control seizures. Fluids or intravenous feeding may be necessary for animals that are dehydrated or severely weakened due to the infection.

Toxoplasmosis is a major concern for people with immune system dysfunction (such as people infected with the human immunodeficiency virus). In these individuals, toxoplasmosis usually leads to inflammation of the brain. Toxoplasmosis is also a major concern for pregnant women because tachyzoites can migrate across the placenta and cause birth defects in human fetuses.

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