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Causes
By Mayo Clinic staff
Rocky Mountain spotted fever is caused by infection with the organism Rickettsia rickettsii. The bacterium infects you when you come in contact with an infected tick in one of these circumstances:
- Tick bites. Rocky Mountain spotted fever most often is spread to humans by tick bites. Ticks can attach themselves to your skin and feed on your blood. They can lodge anywhere on your body, but often are found in your hair, around your ankles and in your genital area. Once embedded in your skin, ticks can cause a small, hard, itchy lump surrounded by a red ring or halo. The longer an infected tick stays attached to your skin, the greater your chance of acquiring infection.
- Broken skin. Rocky Mountain spotted fever can also occur after contact with the bacteria through broken skin, such as a cut or scrape on your hands or fingers. Bacteria that cause this disease circulate in the fluids of a tick's body. If you squeeze or crush a tick as you remove it from yourself, another person or a pet, an infection can occur if the fluid comes in contact with an area of broken skin. It's also possible to develop an infection if you touch your eye after coming into contact with an infected tick.
The culprit ticks
The bacterium that causes Rocky Mountain spotted fever typically is carried by a family of ticks known as Ixodidaeor hard ticks. These ticks live in the low bushes and tall grasses of wooded areas and are more abundant in late spring and early summer.
In the western United States, Rocky Mountain spotted fever is transmitted by the wood tick (Dermacentor andersoni). In the eastern United States, where the disease is most common, it's transmitted by the American dog tick (Dermacentor variabilis). In the southern United States, Central America and South America, Rocky Mountain spotted fever is transmitted by other ticks, such as the cayenne tick (Amblyomma cajennense) and the brown dog tick (Rhipicephalus sanguineus).
Rocky Mountain spotted fever primarily occurs when ticks are most active and during warm weather when people tend to spend more time outdoors.
- Chen LF, et al. What's new in Rocky Mountain spotted fever? Infectious Disease Clinics of North America. 2008;22:415.
- Sexton DJ. Clinical manifestations and diagnosis of Rocky Mountain spotted fever. http://www.uptodate.com/home/index.html. Accessed July 31, 2009.
- Rocky Mountain spotted fever: Questions and answers. Centers for Disease Control and Prevention. http://www.cdc.gov/ticks/disease/rocky_mountain_spotted_fever/faq.htm. Accessed Aug. 3, 2009.
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- Rocky Mountain spotted fever. National Institute of Allergy and Infectious Diseases. http://www3.niaid.nih.gov/topics/rockyMountainSpottedFever/default.htm. Accessed Aug. 3, 2009.
- Centers for Disease Control and Prevention, et al. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis - United States. MMWR Recommendations and Reports. 2006;55:4. http://www.cdc.gov/mmwr/PDF/rr/rr5504.pdf. Accessed Aug. 3, 2009.
- Sexton DJ. Treatment of Rocky Mountain spotted fever. http://www.uptodate.com/home/index.html. Accessed July 31, 2009.
- Removing ticks. Centers for Disease Control and Prevention. http://www.cdc.gov/ticks/tick_removal.html. Accessed Aug. 3, 2009.
