Rocky Mountain spotted fever is an infectious disease caused by bacteria carried by ticks.

Rocky Mountain spotted fever is caused by Rickettsia rickettsii (R. Rickettsii), which is carried by ticks. The bacteria spreads to humans through a tick bite.

In the western United States, the bacteria is carried by the wood tick, and in the eastern U.S. it is carried by the dog tick. However, other ticks spread the infection in the southern U.S. and in Central and South America.

Contrary to the name "Rocky Mountain," most recent cases have been reported in the eastern United States, including North and South Carolina, Virginia, Maryland, Georgia, Tennessee, and Oklahoma. Most cases occur in the spring and summer with about 1,000 cases reported per year. Most of the reported cases have been in children.

Risk factors include recent hiking or exposure to ticks in an area where the disease is known to occur.

Symptoms usually develop about 2 to 14 days after the tick bite. They may include:

• Chills
• Fever
• Severe headache
• Muscle pain
• Mental confusion
• Rash -- usually starts a few days after the fever; first appears on wrists and ankles, then spreads to most of the body; some people do not get a rash

Additional symptoms that may be associated with this disease:

• Abnormal sensitivity to light
• Diarrhea
• Excessive thirst
• Hallucinations
• Loss of appetite
• Nausea
• Vomiting

Tests that may be done include:

• Antibody titer by complement fixation or immunofluorescence
• Kidney function tests
• Platelet count
• Partial thromboplastin time (PTT)
• Prothrombin time (PT)
• Red blood cell count
• Skin biopsy taken from the rash to check for R. rickettsii
• Urinalysis to check for blood in the urine and protein in the urine