Rocky Mountain Spotted Fever

Rocky Mountain Spotted Fever, an acute, potentially fatal infectious disease of humans, caused by the rickettsial organism Rickettsia rickettsii, and transmitted by the wood tick Dermacentor andersoni and the dog tick Dermacentor variabilis. Rocky Mountain spotted fever is so called because it was first recognized in the Rocky Mountain region of the U.S. in 1873. In 1907 the American pathologist Howard Taylor Ricketts proved that the disease is carried by ticks and discovered the causative organism. Cases of the disease have been reported in virtually all states of the U.S.

Most cases of Rocky Mountain spotted fever occur in the spring and summer months. The incubation period of the disease ranges from 2 to 16 days. Treatment with tetracycline or chloramphenicol is usually successful.

The early symptoms of spotted fever are headache and fever. Two to three days after their appearance, a patchy, rose-colored rash appears on the wrists and ankles and rapidly changes color to dark red and brown as it spreads over the rest of the body. The symptoms and signs of this disease are secondary to the invasion by the rickettsial organisms of the cells lining the blood vessels, causing thrombosis of the blood vessels.