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Rocky Mountain
spotted fever is the most severe and most frequently reported
rickettsial illness in the United States. The disease is caused by
Rickettsia rickettsii, a species of bacteria that is spread
to humans by ixodid (hard) ticks. Initial signs and symptoms of the
disease include sudden onset of fever, headache, and muscle pain,
followed by development of rash. The disease can be difficult to
diagnose in the early stages, and without prompt and appropriate
treatment it can be fatal.
Rocky Mountain
spotted fever is somewhat of a misnomer. Beginning in the 1930s, it
became clear that this disease occurred in many areas of the United
States other than the Rocky Mountain region. It is now recognized
that this disease is broadly distributed throughout the continental
United States, as well as southern Canada, Central America, Mexico,
and parts of South America. Between 1981 and 1996, this disease was
reported from every U.S. state except Hawaii, Vermont, Maine, and
Alaska.
Rocky Mountain
spotted fever remains a serious and potentially life-threatening
infectious disease today. Despite the availability of effective
treatment and advances in medical care, approximately 3% to 5% of
individuals who become ill with Rocky Mountain spotted fever still
die from the infection. However, effective antibiotic therapy has
dramatically reduced the number of deaths caused by Rocky Mountain
spotted fever; before the discovery of tetracycline and
chloramphenicol in the late 1940s, as many as 30% of persons
infected with R. rickettsii died.
The organism
that causes Rocky Mountain spotted fever is transmitted by the bite
of an infected tick. The American dog tick (Dermacentor
variabilis) and Rocky Mountain wood tick (Dermacentor
andersoni) are the primary vectors of Rocky Mountain spotted
fever bacteria in the United States.
People
infected with R. rickettsii usually visit a physician in
their first week of illness, following an incubation period of about
5-10 days after a tick bite. The early clinical presentation of
Rocky Mountain spotted fever is often nonspecific and may resemble
many other infectious and non-infectious diseases. Initial symptoms
may include fever, nausea, vomiting, muscle pain, lack of appetite
and severe headache. Later signs and symptoms include rash,
abdominal pain, joint pain, and diarrhea. Three important components
of the clinical presentation are fever, rash, and a previous tick
bite, although one or more of these components may not be present
when the patient is first seen for medical care. Rocky Mountain
spotted fever can be a severe illness, and the majority of patients
are hospitalized.
Rocky Mountain
spotted fever is a seasonal disease and occurs throughout the United
States during the months of April through September. Over half of
the cases occur in the south-Atlantic region of the United States
(Delaware, Maryland, Washington D.C., Virginia, West Virginia, North
Carolina, South Carolina, Georgia, and Florida). The highest
incidence rates have been found in North Carolina and Oklahoma.
Although this disease was reported most frequently in the Rocky
Mountain area early after its discovery, relatively few cases are
reported from that area today.
Rocky
Mountain Fever Diagnosis
A diagnosis of
Rocky Mountain spotted fever is based on a combination of clinical
signs and symptoms and specialized confirmatory laboratory tests.
Other common laboratory findings suggestive of Rocky Mountain
spotted fever include thrombocytopenia, hyponatremia, and elevated
liver enzyme levels.
Rocky
Mountain Fever Treatment
Rocky Mountain
spotted fever is best treated by using a tetracycline antibiotic,
usually doxycycline. This medication should be given in doses of 100
mg every 12 hours for adults or 4 mg/kg body weight per day in two
divided doses for children under 45 kg (100 lbs). Patients are
treated for at least 3 days after the fever subsides and until there
is unequivocal evidence of clinical improvement. Standard duration
of treatment is 5 to 10 days.
Rocky
Mountain Fever Re-Occurrence
Infection with
R. rickettsii is thought to provide long lasting immunity
against re-infection. However, prior illness with Rocky Mountain
spotted fever should not deter persons from practicing good
tick-preventive measures or visiting a physician if signs and
symptoms consistent with Rocky Mountain spotted fever occur,
especially following a tick bite.
Other Pages with information on Rocky Mountain Spotted Fever:
Rocky
Mountain Spotted Fever - History
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Rocky Mountain Spotted Fever Overview
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Rocky
Mountain Spotted Fever The Organism
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Rocky Mountain Spotted Fever
Epidemiology
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Rocky Mountain Spotted Fever
Signs and Symptoms
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Rocky Mountain spotted fever
Detection
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Rocky Mountain Spotted Fever
Treatment
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Rocky Mountain Spotted Fever
Prevention and Control
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