(Spotted Fever; Tick Fever; Tick Typhus)
Topic Resources
Rocky Mountain spotted fever
is a potentially fatal rickettsial infection that is transmitted by dog
ticks and wood ticks. It causes a rash, headache, and high fever.
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People become infected when a tick carrying the infection bites them.
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A severe headache, chills, extreme exhaustion, and muscle pains develop, usually followed a few days later by a rash.
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Avoiding tick bites is the best way to prevent the infection.
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People are given antibiotics immediately if they have been bitten by a tick and have typical symptoms.
Rocky Mountain spotted fever (RMSF) is caused by the bacteria Rickettsia rickettsii. Rickettsiae are a type of bacteria that can live only inside the cells of other organisms.
Rocky Mountain spotted fever is probably the most common
rickettsial infection in the United States. It was first recognized in
the Rocky Mountain states but occurs throughout most of the continental
United States. It is most common in the southeastern and south central
United States (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. In the southern states, the disease may occur
throughout the year. The infection is more common among people who spend
a lot of time in tick-infested areas and among children younger than
15.
Ticks acquire these rickettsiae by feeding on infected mammals,
typically rodents. 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.
Wood Tick
Image courtesy of Dr. Christopher Paddock via the Public Health Image Library of the Centers for
Disease Control and Prevention.
Yellow Dog Tick
Image courtesy of Dr. Christopher Paddock via the Public Health Image Library of the Centers for Disease Control and Prevention.
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. If the infection is severe,
blood clots may form throughout the body, causing disseminated intravascular coagulation.
Symptoms
Typically, symptoms of Rocky Mountain spotted fever include a
severe headache, chills, extreme exhaustion (prostration), and muscle
pains. Symptoms begin suddenly 3 to 12 days after a tick bite. The more
quickly symptoms begin, the more severe the infection. A high fever
develops within several days and, in severe infections, persists for 2
to 3 weeks. A hacking, dry cough may also develop. Nausea and vomiting
are common.
Between the first and the sixth day of the fever, a rash appears
on the 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 4 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.
About 10% of people with Rocky Mountain spotted fever do not develop a rash.
Rocky Mountain Spotted Fever
Image courtesy of the Public Health Image Library of the Centers for Disease Control and Prevention.
As Rocky Mountain spotted fever progresses, it may cause other symptoms:
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Restlessness, insomnia, delirium, or sometimes coma if the blood vessels in the brain are affected
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Abdominal pain
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Inflammation of the airways (pneumonitis) and pneumonia
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Heart damage
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Anemia
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Severe low blood pressure and death (uncommonly, when the infection is severe)
Diagnosis
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A doctor's evaluation
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Biopsy and testing of the rash
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Blood tests
Doctors suspect Rocky Mountain spotted fever if people do both of the following:
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Live in or near a wooded area anywhere in the Western Hemisphere
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Have a fever, headache, and muscle aches in the spring, summer, or fall, regardless of whether they have a rash or a tick bite
About 70% of people remember being bitten by a tick.
Testing is usually required to confirm Rocky Mountain spotted
fever. However, available tests may not detect the bacteria right away
or take a long time to process. Thus, if doctors suspect Rocky Mountain
spotted fever, they typically start treatment before they get test
results.
To confirm the diagnosis, doctors usually do an immunofluorescence assay
on a sample taken from the rash (biopsy). For immunofluorescence
assays, foreign substances produced by the bacteria (antigens) are
labeled with a fluorescent dye making the bacteria easier to detect and
identify.
Doctors may do blood tests that detect antibodies to the
bacteria. However, these tests can first detect these antibodies only
about 7 to 10 days after symptoms begin. Antibody tests done before this
time may be negative. So doctors usually do the test twice several
weeks apart to check for an increase in the antibody level. Thus,
these tests do not help doctors diagnose the infection immediately
after someone becomes ill but can help confirm the diagnosis later.
Prevention
There is no vaccine against Rocky Mountain spotted fever, so
avoiding tick bites and immediately removing attached ticks are the best
prevention. The following measures can help:
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Tucking trousers into boots or socks and applying insecticide that contains permethrin to clothing limits tick access to skin.
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Tick repellents such as DEET (diethyltoluamide) may be applied to the skin. These repellents are effective but, rarely, cause toxic reactions, such as seizures, in young children.
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Searching frequently for ticks helps prevent infection because the tick must be attached for 24 hours on average to transmit infection.
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Attached ticks should be removed carefully with tweezers. The head of the tick should be grasped as close to the skin as possible. Care must be taken when removing a tick because rickettsiae may be transmitted if an infected tick that is engorged with blood is crushed while being removed.
Tick Bite Prevention
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Preventing tick access to skin includes
DEET should be used cautiously in very young children because toxic reactions have been reported. 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.
Engorged ticks 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.
Gradual traction on the head with a small forceps dislodges the tick. The point of attachment should be swabbed with alcohol. Petroleum jelly, lit matches, and other irritants are not effective ways to remove ticks and should not be used.
No practical means are available to rid entire areas of ticks.
However, the number of ticks may be reduced in areas where it is common
by making the environment less appealing to the animals that carry the
ticks. For example, people can make areas less appealing to mice by
removing wood piles and leaf litter and clearing tall grasses and brush
around homes, especially around play areas. Mice can hide and nest in
such places.
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Treatment
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Antibiotics
Doctors immediately prescribe antibiotics if they suspect Rocky
Mountain fever based on symptoms and the potential for exposure to
infected ticks—even if laboratory test results are not yet available.
Early treatment with antibiotics has reduced the death rate from about
20% to 5%.
Doxycycline is usually
used. It is given by mouth when the infection is mild and intravenously
when it is more severe. People take the antibiotic until they improve
and have had no fever for 24 to 48 hours, but they must take it for at
least 7 days.
However, 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.
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