Rocky Mountain spotted fever
Spotted fever
Rocky Mountain spotted fever (RMSF) is a disease caused by a type of bacteria carried by ticks.
This is the appearance of the rash of Rocky Mountain Spotted Fever on the hands and forearms. The rash starts on the hands and feet and later spreads to the trunk. It is caused by a bacteria transmitted to humans by a tick bite. (Image courtesy of the Centers for Disease Control and Prevention.)
Diseases are often carried by ticks, including Rocky Mountain Spotted Fever, Colorado Tick Fever, Lyme disease, and tularemia. Less common or less frequent diseases include typhus, Q-fever, relapsing fever, viral encephalitis, hemorrhagic fever, and babesiosis.
There are many species of ticks. Of these, a large proportion are capable of carrying disease. Diseases carried by ticks include Lyme disease, Erlichiosis, Rocky Mountain Spotted Fever, Colorado Tick Fever, tularemia, typhus, hemorrhagic fever, and viral encephalitis. (Image courtesy of the Centers for Disease Control and Prevention.)
Rocky Mountain Spotted Fever is a disease transmitted to humans by a tick bite. The spots begin as flat (macular) red (erythematous) patches that may bleed into the skin, causing purplish spots (purpura). The disease is named after its characteristic spots. (Image courtesy of the Centers for Disease Control and Prevention.)
This is a close-up photograph of a tick embedded in the skin. Ticks are important because they can carry diseases such as Rocky Mountain spotted fever, tularemia, Colorado tick fever, Lyme disease, and others.
Rocky Mountain spotted fever is caused by the organism Rickettsia rickettsii and is transmitted by a tick bite. It is a serious infection that produces a classical rash in about 90% of infected individuals. This is the typical appearance of the rash. There are many symptoms that affect the entire body (systemic).
Rocky Mountain Spotted Fever is a potentially fatal infection transmitted to humans by ticks. This photograph shows the classical appearing rash which often begins on the wrists and ankles, and spreads rapidly towards the center of the body. The rash may also be present on the palms and soles.
Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy substances containing antigens.
Causes
RMSF is caused by the bacterium Rickettsia rickettsii (R Rickettsii), which is carried by ticks. The bacteria is spread to humans through a tick bite.
In the western United States, the bacteria are carried by the wood tick. In the eastern US, they are carried by the dog tick. Other ticks spread the infection in the southern US and in Central and South America.
Contrary to the name "Rocky Mountain," most recent cases have been reported in the eastern US. States include North and South Carolina, Virginia, Georgia, Tennessee, and Oklahoma. Most cases occur in the spring and summer and are found 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 ticks carry the bacteria. Bacteria can also infect people who crush ticks they have removed from pets with their bare fingers. Not all people will remember getting a tick bite.
Symptoms
Symptoms usually develop about 2 to 14 days after the tick bite. They may include:
- Chills and fever
- Confusion
- Headache
- Muscle pain
- Rash -- usually starts a few days after the fever; first appears on wrists and ankles as spots that are 1 to 5 mm in diameter, then spreads to most of the body. Some infected people don't get a rash.
Other symptoms that may occur with this disease:
Exams and Tests
Your health care provider will perform a physical examination and ask about your symptoms.
Tests that may be done include:
- Antibody titer by complement fixation 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
Treatment involves antibiotics and carefully removing the tick from the skin. To get rid of the infection, antibiotics such as doxycycline or tetracycline need to be taken. Pregnant women are usually prescribed chloramphenicol.
Outlook (Prognosis)
Treatment usually cures the infection. About 3% of people who get this disease will die.
Possible Complications
Untreated, the infection may lead to health problems such as:
- Brain damage
- Clotting problems
- Heart failure
- Kidney failure
- Lung failure
- Meningitis
- Pneumonitis (lung inflammation)
- Shock
When to Contact a Medical Professional
Contact your provider if you develop symptoms after exposure to ticks or a tick bite. The complications of untreated RMSF are often life threatening.
Prevention
When walking or hiking in tick-infested areas, tuck long pants into socks to protect the legs. 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.
Remove ticks immediately by using tweezers, pulling carefully and steadily. Insect repellent may be helpful. Because only about 1 in 1,000 ticks carry this infection, antibiotics are not usually given after a tick bite.
References
Blanton LS, Walker DH. Rickettsia rickettsii and other spotted fever group rickettsiae (Rocky Mountain spotted fever and other spotted fevers). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 186.
Bolgiano EB, Sexton J. Tickborne illnesses. In: Walls RM, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 123.
Version Info
Last reviewed on: 5/19/2023
Reviewed by: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
