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Rocky Mountain spotted fever

Rocky Mountain spotted fever is the most severe and most frequently reported rickettsial illness in the United States, and has been diagnosed throughout the Americas. more...

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Some synonyms for Rocky Mountain spotted fever in other countries include "tick typhus", "Tobia fever" (Columbia), "São Paulo fever" and "febre maculosa" (Brazil), and "fiebre manchada" (Mexico). The disease is caused by Rickettsia rickettsii, a species of bacteria that is spread to humans by hard ticks (Ixodidae). 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.

Howard T. Ricketts was the first to establish the identity of the infectious organism that causes this disease. He and others characterized the basic epidemiological 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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Rocky Mountain spotted fever
From Gale Encyclopedia of Medicine, 4/6/01 by Rosalyn S. Carson-DeWitt


Rocky Mountain spotted fever (RMSF) is a tick-borne illness caused by a bacteria, resulting in a high fever and a characteristic rash.


The bacteria causing RMSF is passed to humans through the bite of an infected tick. The illness begins within about two weeks of such a bite. RMSF is the most widespread tick-borne illness in the United States, occurring in every state except Alaska and Hawaii. The states in the mid-Atlantic region, the Carolinas, and the Virginias have a great deal of tick activity during the spring and summer months, and the largest number of RMSF cases come from those states. About 5% of all ticks carry the causative bacteria. Children under the age of 15 years have the majority of RMSF infections.

Causes & symptoms

The bacterial culprit in RMSF is called Rickettsia rickettsii. It causes no illness in the tick carrying it, and can be passed on to the tick's offspring. When a tick attaches to a human, the bacteria is passed. The tick must be attached to the human for about six hours for this passage to occur. Although prompt tick removal will cut down on the chance of contracting RMSF, removal requires great care. If the tick's head and body are squashed during the course of removal, the bacteria can be inadvertently rubbed into the tiny bite wound.

Symptoms of RMSF begin within two weeks of the bite of the infected tick. Symptoms usually begin suddenly, with high fever, chills, headache, severe weakness, and muscle pain. Pain in the large muscle of the calf is very common, and may be particularly severe. The patient may be somewhat confused and delirious. Without treatment, these symptoms may last two weeks or more.

The rash of RMSF is quite characteristic. It usually begins on the fourth day of the illness, and occurs in at least 90% of all patients with RMSF. It starts around the wrists and ankles, as flat pink marks (called macules). The rash spreads up the arms and legs, toward the chest, abdomen, and back. Unlike rashes which accompany various viral infections, the rash of RMSF does spread to the palms of the hands and the soles of the feet. Over a couple of days, the macules turn a reddish-purple color. They are now called petechiae, which are tiny areas of bleeding under the skin (pinpoint hemorrhages). This signifies a new phase of the illness. Over the next several days, the individual petechiae may spread into each other, resulting in larger patches of hemorrhage.

The most severe effects of RMSF occur due to damage to the blood vessels, which become leaky. This accounts for the production of petechiae. As blood and fluid leak out of the injured blood vessels, other tissues and organs may swell and become damaged, and:

  • Breathing difficulties may arise as the lungs are affected.
  • Heart rhythms may become abnormal.
  • Kidney failure occurs in very ill patients.
  • Liver function drops.
  • The patient may experience nausea, vomiting, abdominal pain, and diarrhea.
  • The brain may swell (encephalitis) in about 25% of all RMSF patients. Brain injury can result in seizures, changes in consciousness, actual coma, loss of coordination, imbalance on walking, muscle spasms, loss of bladder control, and various degrees of paralysis.
  • The clotting system becomes impaired, and blood may be evident in the stools or vomit.


Diagnosis of RMSF is almost always made on the basis of the characteristic symptoms, coupled with either a known tick bite (noted by about 60-70% of patients) or exposure to an area known to harbor ticks. Complex tests exist to nail down a diagnosis of RMSF, but these are performed in only a few laboratories. Because the results of these tests take so long to obtain, they are seldom used. This is because delaying treatment is the main cause of death in patients with RMSF.


It is essential to begin treatment absolutely as soon as RMSF is seriously suspected. Delaying treatment can result in death.

Antibiotics are used to treat RMSF. The first choice is a form of tetracycline; the second choice (used in young children and pregnant women) is chloramphenicol. If the patient is well enough, treatment by oral intake of medicine is perfectly effective. Sicker patients will need to be given the medication through a needle in the vein (intravenously). Penicillin and sulfa drugs are not suitable for treatment of RMSF, and their use may increase the death rate by delaying the use of truly effective medications.

Very ill patients will need to be hospitalized in an intensive care unit. Depending on the types of complications a particular patient experiences, a variety of treatments may be necessary, including intravenous fluids, blood transfusions, anti-seizure medications, kidney dialysis, and mechanical ventilation (a breathing machine).

Alternative treatment

Although alternative treatments should never be used in place of conventional treatment with antibiotics, they can be useful adjuncts to antibiotic therapy. The use of Lactobacillus acidophilus and L. bifidus supplementaion during and after antibiotic treatment can help rebalance the intestinal flora. Acupuncture, homeopathy, and botanical medicine can all be beneficial supportive therapies during recovery from this disease.


Prior to the regular use of antibiotics to treat RMSF, the death rate was about 25%. Although the death rate from RMSF has improved greatly with an understanding of the importance of early use of antibiotics, there is still a 5% death rate. This rate is believed to be due to delays in the administration of appropriate medications.

Certain risk factors suggest a worse outcome in RMSF. Death rates are higher in males and increase as people age. It is considered a bad prognostic sign to develop symptoms of RMSF within only two to five days of a tick bite.


The mainstay of prevention involves avoiding areas known to harbor ticks. However, because many people enjoy recreational activities in just such areas, other steps can be taken:

  • Wear light colored clothing (so that attached ticks are more easily noticed).
  • Wear long sleeved shirts and long pants; tuck the pants legs into socks.
  • Spray clothing with appropriate tick repellents.
  • Examine. Anybody who has been outside for any amount of time in an area known to have a population of ticks should examine his or her body carefully for ticks. Parents should examine their children at the end of the day.
  • Remove any ticks using tweezers, so that infection doesn't occur due to handling the tick. Grasp the tick's head with the tweezers, and pull gently but firmly so that the head and body are entirely removed.
  • Keep areas around homes clear of brush, which may serve to harbor ticks.

Key Terms

Inflammation of the tissues of the brain.
A flat, discolored area on the skin.
A small, round, reddish purple spot on the skin, representing a tiny area of bleeding under the skin.

Further Reading

For Your Information


  • Corey, Lawrence. "Rickettsia and Coxiella." In Sherris Medical Microbiology: An Introduction to Infectious Diseases, edited by Kenneth J. Ryan. Norwalk, CT: Appleton and Lange, 1994.
  • Stoffman, Phyllis. The Family Guide to Preventing and Treating 100 Infectious Diseases.New York: John Wiley and Sons, 1995.
  • Walker, David, et al. "Rickettsial Diseases." In Harrison's Principles of Internal Medicine, 14th ed., edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.


  • Kalish, Robert. "How to Recognize and Treat Tick-Borne Infections." Patient Care 31 (May 15, 1997): 184+.
  • Lyon, G. Marshall, and Anita M. Kelsey. "Rocky Mountain Spotted Fever." Consultant 36 (August 1996): 1729+.
  • "Other Tick-Bite Ailments." American Health 14 (June 1995): 78+.
  • "Rocky Mountain Spotted Fever: A Disease For All Seasons--and All Parts of the Country." Consultant 35 (September 1995): 1318.


  • Centers for Disease Control and Prevention. (404) 332-4559.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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