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. The brown dog tick also transmits the disease in some parts of the country (including Arizona) and in other countries.
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, 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, impaired balance, and increased painful spinal sensitivity from a normally painless touch, may be seen. Between 1% and 10% of dogs with Rocky Mountain spotted fever die from the disease.
Blood tests that assess antibody levels are used to diagnose Rocky Mountain spotted fever. If a veterinarian suspects the disease, antibiotic treatment is usually 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 bleeding 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. It is important to remember that contact with fluids and excretions from infected ticks can spread the disease to people.
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