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Rocky Mountain Spotted Fever (Tick Fever) 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 Rocky Mountain spotted fever.

Rocky Mountain spotted fever is a disease of humans and dogs that is caused by Rickettsia rickettsii. (Rickettsiae are a specialized type of bacteria that live only inside other cells.) The spotted-fever group of organisms is found worldwide, but the closely related organisms within this group that cause Rocky Mountain spotted fever are only found in certain geographic areas of North, South, and Central America. They are often transmitted through the bites of infected ticks. In the United States, the American dog tick and the Rocky Mountain wood tick are considered the most important transmission agents for Rickettsia rickettsii.

Direct transmission from dogs to humans has not been reported. Humans can become infected following contact with tick blood and lymph fluids or excretions during the removal of engorged ticks from their pets or themselves. Human infections usually involve the transfer of tick fluids through broken skin or through the eyes.

Dogs are highly susceptible to infection. Early signs may include fever (up to 105°F [40.5°C]), loss of appetite, enlargement of the lymph nodes, inflammation of several joints together, coughing or difficulty in breathing, abdominal pain, vomiting and diarrhea, and swelling of the face or extremities. In severe cases, unraised, perfectly round, purplish red spots may be seen on the linings of the eyelids and mouth. These spots are caused by bleeding below the surfaces of these tissues. Signs of nervous system involvement, such as altered mental states and increased painful spinal sensitivity from a normally painless touch, may be seen. Between 1% and 5% of dogs with Rocky Mountain spotted fever die from the disease.

If a veterinarian suspects Rocky Mountain spotted fever, antibiotic treatment is usuallly started immediately without waiting for blood test results. Any delay in treatment may increase the chances of a severe or fatal infection. Depending on the severity of infection, supportive care for dehydration and hemorrhaging may be necessary.

The most important preventive steps are those that control ticks, the most common source of the disease. Keeping your dog away from areas known to harbor ticks is a step you can take. Preventive medications that will keep your dog from being infested with ticks are also available from your veterinarian. Any ticks found on your dog should be promptly and properly removed to prevent the spread of disease. Remove any ticks by using fine-pointed tweezers to grasp the head of the tick (right where it enters the skin). Pull the tick straight off, making sure not to grasp or squeeze its body. If there are multiple ticks, it may be best to have your veterinarian remove them and examine your dog.