| 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 was first recognized in 1896 in the Snake
River Valley of Idaho and was originally called
"black measles" because of the characteristic
rash. It was a dreaded and frequently fatal disease that
affected hundreds of people in this area. By the early
1900s, the recognized geographic distribution of this
disease grew to encompass parts of the United States as
far north as Washington and Montana and as far south as
California, Arizona, and New Mexico.
In response to this severe problem, the Rocky Mountain
Laboratory was established in Hamilton, Montana.
This facility is now run by the National Institute of
Allergy and Infectious Diseases, National Institutes of
Health. Researchers there continue to study Rocky
Mountain spotted fever and other diseases.
Laboratory and epidemiologic studies were also carried
out by the Communicable Disease Center (now the Centers
for Disease Control and Prevention, or CDC) and are
currently conducted by scientists in the Viral and
Rickettsial Zoonoses Branch, Division of Viral and
Rickettsial Diseases, National Center for Infectious
Diseases, CDC.
Howard T. Ricketts was the first to establish the
identity of the infectious organism that causes this
disease. He and others characterized the basic
epidemiologic features of the disease, including the role
of tick vectors. Their studies found that Rocky Mountain
spotted fever is caused by Rickettsia rickettsii.
This species is maintained in nature by a complex cycle
involving ticks and mammals; humans are considered to be
accidental hosts and are not involved in the natural
transmission cycle of this pathogen. Tragically,
Dr. Ricketts died of typhus (another rickettsial disease)
in Mexico in 1910, shortly after completing his
remarkable studies on Rocky Mountain spotted fever.
The name 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.
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