Rocky Mountain spotted fever is a potentially fatal rickettsial infection that is caused by Rickettsia rickettsii bacteria and transmitted by infected dog ticks and wood ticks.
People become infected when they are bitten by an infected tick.
Symptoms occur suddenly and include severe headache, chills, extreme exhaustion, and muscle pains that are usually followed by a rash.
To diagnose the infection, doctors do blood tests.
The antibiotic doxycycline is given as soon as doctors suspect a person has Rocky Mountain spotted fever.
Avoiding tick bites is the best way to prevent the infection.
Rocky Mountain spotted fever is caused by the bacteria Rickettsia rickettsii. Rickettsiae are a type of bacteria that can live and multiply only inside the cells of a host organism, such as an animal or a person, and cannot survive on their own in the environment. For Rickettsia rickettsii, the primary host is a tick, and secondary hosts include rodents, dogs, and humans.
Rickettsiae live and multiply in the cells lining blood vessels. Blood vessels in and under the skin and in the brain, lungs, heart, kidneys, liver, and spleen are commonly infected. Small infected blood vessels may become blocked by blood clots.
Rocky Mountain spotted fever was first recognized in the Rocky Mountain states but occurs throughout most of the continental United States. It occurs year-round in North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri. It also occurs in Central and South America.
Rocky Mountain spotted fever occurs mainly from March to September, when adult ticks are active and people are likely to be in tick-infested areas. The infection is more common among people who spend a lot of time in tick-infested areas and among people over 40.
Ticks are the primary host of Rickettsia rickettsii bacteria. Uninfected ticks can acquire these rickettsiae by feeding on infected mammals, typically rodents and canines (for example, dogs, wild dogs, and coyotes). Infected female ticks can also transmit rickettsiae to their offspring. Infection is spread to people through bites by wood ticks or dog ticks. Rickettsial infection is probably not transmitted directly from person to person.
This photo shows a wood tick, which transmits the bacteria that cause Rocky Mountain spotted fever.
CDC/James Gathany
This photo shows a yellow dog tick, which transmits the bacteria that cause Rocky Mountain spotted fever.
CDC/James Gathany
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Symptoms of Rocky Mountain Spotted Fever
Typically, symptoms of Rocky Mountain spotted fever occur suddenly and include a severe headache, chills, extreme exhaustion (prostration), and muscle pains. Symptoms begin 3 to 12 days after a tick bite. The more quickly symptoms begin after the bite, the more severe the infection. A high fever of 103.1 to 104° F (39.5 to 40° C) develops within several days and, in severe infections, remains high for 15 to 20 days. Nausea and vomiting are common.
By the sixth day of the fever, most people develop a rash on their wrists, palms, ankles, soles, and forearms. It rapidly extends to the neck, face, armpits, buttocks, and trunk. At first, the rash is flat and pink but later darkens and becomes slightly raised. It does not itch. Warm water—for example, in a bath—makes the rash more evident. In about 5 or 6 days, small purplish areas (petechiae) develop because of bleeding in the skin. If the infection is severe, areas of skin may die and turn black, indicating gangrene.
This photo shows a rash characterized by small purplish areas (petechiae) that extends across the arm. This rash is typical of Rocky Mountain spotted fever.
This photo shows a rash characterized by small purplish areas (petechiae) that extends across the arm. This rash is typ
CDC
This photo shows the characteristic rash of Rocky Mountain spotted fever (RMSF).
This photo shows the characteristic rash of Rocky Mountain spotted fever (RMSF).
CDC
This photo shows the characteristic rash of Rocky Mountain spotted fever (RMSF).
This photo shows the characteristic rash of Rocky Mountain spotted fever (RMSF).
CDC
This photo shows a rash characterized by small purplish areas (petechiae) that extends across the arm. This rash is typical of Rocky Mountain spotted fever.
This photo shows a rash characterized by small purplish areas (petechiae) that extends across the arm. This rash is typ
CDC
This photo shows the characteristic rash of Rocky Mountain spotted fever (RMSF).
This photo shows the characteristic rash of Rocky Mountain spotted fever (RMSF).
CDC
This photo shows the characteristic rash of Rocky Mountain spotted fever (RMSF).
This photo shows the characteristic rash of Rocky Mountain spotted fever (RMSF).
CDC
As Rocky Mountain spotted fever progresses, it may cause other symptoms:
Restlessness, insomnia, delirium, or sometimes coma if the blood vessels in the brain are affected
Abdominal pain
Inflammation of the airways (pneumonitis) and pneumonia
Heart damage
Anemia
Low blood pressure and death (when the infection is severe)
Diagnosis of Rocky Mountain Spotted Fever
A doctor's evaluation
Biopsy and testing of the rash
Blood tests
Doctors suspect Rocky Mountain spotted fever if people do both of the following:
Live or work in or near or have travelled to a wooded area anywhere in the Western Hemisphere
Have a fever, headache, and muscle aches, regardless of whether they have a rash or a tick bite
Although the infection is always transmitted by ticks, many people do not remember being bitten by a tick.
To confirm the diagnosis, doctors usually do the polymerase chain reaction (PCR) technique or an immunofluorescence assay on a sample of blood. An immunofluorescence assay is a test that detects antibodies to the Rickettsia rickettsii bacteria. The PCR technique makes copies of the bacteria's DNA, so that the bacteria can be detected more rapidly.
Sometimes doctors remove a sample of the rash (biopsy) and test if for antigens produced by the bacteria. See also Tests That Detect Antibodies to or Antigens of Microorganisms.
Treatment of Rocky Mountain Spotted Fever
Antibiotics
Doctors immediately prescribe antibiotics if they suspect a person has Rocky Mountain spotted fever before test results are available. A delay in treatment may lead to serious complications, including death.
Doctors typically give people of all ages, including children and pregnant people, the antibiotic doxycycline. It is given by mouth when the infection is mild and by vein when it is more severe. People take the antibiotic until they improve and have not had a fever for at least 3 days. After this point, people continue to take doxycycline for 5 to 7 days.
Although doxycycline can cause tooth staining in children younger than 8 years old, a short 5- to 10-day course in children of all ages is recommended by the American Academy of Pediatrics and can be used without causing tooth staining or weakening of tooth enamel.
A doctor usually does not prescribe antibiotics for people who have had a tick bite but have no symptoms. Instead, the doctor may ask them to immediately report any symptoms.
Pregnant people should review with their doctor the potential risks versus benefits of taking doxycycline for Rocky Mountain spotted fever.
Prevention of Rocky Mountain Spotted Fever
There is no vaccine against Rocky Mountain spotted fever.
To prevent this infection, people should take measures to prevent tick bites. (See also the Centers for Disease Control and Prevention: Preventing Tick Bites.)
Preventing tick access to skin includes:
Staying on paths and trails
Tucking trousers into boots or socks
Wearing long-sleeved shirts
Applying repellents that contain diethyltoluamide (DEET), picaridin, IR3535, oil of lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone to skin surfaces
Treating clothing, shoes/boots, and gear with permethrin
Some repellents can be toxic to children, so DEET should not be used in infants under 2 months of age, and repellents that contain more than 10% DEET should not be used in children under 12 years of age. OLE and PMD should not be used in children under 3 years of age. Permethrin on clothing effectively kills ticks. Frequent searches for ticks, particularly in hairy areas and on children, are essential in areas where infections transmitted by ticks are common.
Ticks should be removed as soon as possible. An engorged tick should be removed with care and not crushed between the fingers because crushing the tick may result in disease transmission. The tick’s body should not be grasped or squeezed. Removal is best accomplished by grasping the tick with curved tweezers as close to the skin as possible and pulling it directly out. The tick’s head, which may not come out with the body, should be removed, because it can cause prolonged inflammation. The area where the tick was attached and the hands of the person removing the tick should be disinfected with soap and water, rubbing alcohol, or hand sanitizer. Petroleum jelly, lit matches, and other irritants are not effective ways to remove ticks and should not be used.
Ticks cannot be entirely eliminated from large areas in the environment. However, the number of ticks may be reduced by taking steps to remove or prevent tick habitats and by making the environment less appealing and accessible to the animals that carry ticks. Ticks are often found in wood piles, leaf litter, tall grasses, and brush, so people can reduce the number of ticks in their yard by clearing such debris from around their home, especially outdoor play areas. Regular lawn maintenance, including frequent lawn mowing, is key to keeping ticks out of recreational areas and yards. People should remove any trash or unused furniture from their yard, and move outdoor equipment, toys, and seating away from shaded yard edges and trees. People can also install a 3-foot wide barrier of wood chips or gravel between their lawn and wooded areas.
To discourage tick-carrying rodents (such as rats, mice, and squirrels) from entering the yard, people should stack firewood in dry, elevated areas. To discourage other tick-carrying animals, such as raccoons, deer, and stray dogs, from entering the yard, people can install a fence.
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