Rocky Mountain spotted fever

Rocky Mountain spotted fever is a disease brought on by a type of bacteria carried by ticks.

Spotted fever

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

In the western United States, the bacteria are carried by the wood tick, and in the eastern U.S. they are carried by the dog tick. 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. About 2,300 cases were reported in 2006. 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. The bacteria are unlikely to be transmitted to a person by a tick that has been attached for less than 20 hours. Only about 1 in 1,000 wood and dog ticks carry the bacteria. Bacteria can also infect people who crush ticks they have removed from pets with their bare fingers.

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

• Chills
• Confusion
• Fever
• Headache
• Muscle pain
• Rash -- usually starts a few days after the fever; first appears on wrists and ankles as spots that are 1 - 5 mm in diameter, then spreads to most of the body. About one-third of infected people do not get a rash.

Other symptoms that may occur with this disease:

• Diarrhea
• Light sensitivity
• Hallucinations
• Loss of appetite
• Nausea
• Thirst
• Vomiting

Tests that may be done include:

• Antibody titerby complementfixation or immunofluorescence
• Complete blood count (CBC)
• Kidney function tests
• Partial thromboplastin time (PTT)
• Prothrombin time (PT)
• Skin biopsy taken from the rash to check for R. rickettsii
• Urinalysis to check for blood or protein in the urine

Treatment involves careful removal of the tick from the skin and antibiotics to get rid of the infection. Doxycycline or tetracycline are the drugs of choice for both confirmed and suspected cases. Pregnant women may take chloramphenicol.

Note: There is concern that tetracycline and doxycycline may stain the teeth of children whose permanent teeth have not yet formed. However, tooth discoloration is very unusual when a child takes these medicines for 14 days or less. These medicines are first-line treatment, even for children.

Treatment usually cures the infection. Complications are rare, but can include paralysis, hearing loss, and nerve damage. About 3% of people who get this disease will die.

• Brain damage
• Clotting problems
• Heart failure
• Kidney failure
• Lung failure
• Meningitis
• Pneumonitis (lung inflammation)
• Shock

Call your health care provider if you develop symptoms after exposure to ticks or a tick bite. The complications of untreated Rocky Mountain spotted fever are often life threatening.

When walking or hiking in tick-infested areas, tuck long pants into socks to protect the legs, and wear shoes and long-sleeved shirts. Ticks will show up on white or light colors better than on dark colors, making them easier to see and remove from clothing.

Remove ticks immediately by using a tweezers, pulling carefully and steadily. Insect repellent may be helpful. Because far fewer than 1% of ticks carry this infection, antibiotics are not usually given after a tick bite.

Raoult D. Rickettsioses. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 348.

Walker DH. Rickettsia rickettsii and other spotted fever group rickettsiae (rocky mountain spotted fever and other spotted fevers). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 187.

Review Date: 06/09/2011

David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Mediicne, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.