eMedicine Specialties > Dermatology > Bacterial Infections

Rocky Mountain Spotted Fever

Author: Nicole L Lacz, MD, Chief Resident, Department of Radiology, St Barnabas Medical Center
Coauthor(s): Robert A Schwartz, MD, MPH, Professor and Head, Dermatology, Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health, UMDNJ-New Jersey Medical School; Rajendra Kapila, MD, MBBS, Professor of Medicine, Department of Medicine, UMDNJ, New Jersey Medical School
Contributor Information and Disclosures

Updated: Jun 26, 2009

Introduction

Background

All rickettsioses are classified as zoonoses with arthropods as the natural host. The rickettsiae organisms causing the spotted fever group of diseases are tick-borne with transovarial and transstadial passage. Humans are accidental hosts.1

Rocky Mountain spotted fever (RMSF) is the most commonly reported rickettsial disease. It is caused by the obligate intracellular pathogen, Rickettsia rickettsii. Initial descriptions of the disease, then referred to as "black measles," date back to 1896 in the Snake River Valley of Idaho. Not until the early 1900s did Howard T. Ricketts (who ironically died of the rickettsial disease, typhus, in 1910) identify the causative agent, while the geographic distribution of the disease grew throughout the midwest region of the country. Contrary to its name, the disease has been reported throughout the United States, with the exceptions of Maine and Vermont.

Despite advances in health care and effective treatment options, RMSF remains a killer for a small percentage of those affected. As a prevalent and potentially fatal infection, RMSF is an important condition to recognize, especially because of the difficult clinical diagnosis and the lack of a variety of sensitive and specific diagnostic tests available in the acute stage.

Pathophysiology

Endothelial cells are important components of vessel walls that function to provide vascular tone, angiogenesis, and proper inflammatory responses and to aid in normal hemostasis. Because of the tropism of R rickettsii for the endothelium, the organism spreads centripetally, cell to cell via filopodia propulsion, resulting in injury to the microcirculation (small-to-medium–sized vessels) of various organ systems with little host response. The organism is able to replicate within the nucleus or cytoplasm of host cells. R rickettsii attaches to and invades the vascular endothelial and smooth muscle cells of many organs, including the brain, liver, skin, lungs, kidneys, and gastrointestinal tract, which may lead to major complications.

The pulmonary interstitial pneumonia, which may complicate Rocky Mountain spotted fever (RMSF), may be the direct result of pulmonary microcirculation vasculitis. Similarly, vascular injury–induced myocardial edema has emerged as the likely cause of myocarditis occurring with RMSF. Portal triaditis and vasculitis have been found in liver specimens during postmortem examination. Vascular injury of the pancreas and the gastrointestinal tract, including the stomach, the small intestine, and the colon, may result in nausea, vomiting, diarrhea, and abdominal cramping. The emergence of such common and nonspecific gastrointestinal symptoms early in the disease may lead to diagnostic confusion.

Infected endothelial cells display an activated phenotype causing hemostatic system changes that may result in severe coagulopathies. Up-regulation of gene expression for proinflammatory and procoagulation proteins occurs. Activation of the coagulation cascade with thrombin production, platelet activation, increased antifibrinolytic factors, and anticoagulant factor consumption leads to a hypercoagulable state. Note that most patients with RMSF will have thrombocytopenia and abnormal liver function test results as a consequence of these system disruptions. Infected endothelial cells also generate oxygen free radicals. Leaking of blood through vessel walls into adjacent tissue creates the rash for which RMSF is known.

Frequency

United States

Rocky Mountain spotted fever (RMSF) is the most common fatal tick-borne disease in the United States. Approximately 1253 cases occurred from 1993-1996, which calculates to an annual incidence of 2.2 cases per million persons. Although RMSF has been a reportable illness with data compiled by the US Centers for Disease Control and Prevention (CDC) since the 1920s, the number of cases may be grossly underreported considering some infections with R rickettsii may be subclinical. Approximately 45-52% of confirmed cases come from the South Atlantic region of the United States, with Oklahoma, Tennessee, North Carolina, and South Carolina ranking highest. Of note, the Rocky Mountain states have only contributed to approximately 3% of total reported cases in recent years. Approximately 90% of cases occur between April and September.2,3

International

Canada, Mexico, Central America, Colombia, and Brazil are all areas with widespread infection by R rickettsii; however, the vectors differ. The principal vector in South America is Amblyomma cajennense, whereas Rhipicephalus sanguineous is the primary vector in Mexico and Central America.4 Dermacentor variabilis (American dog tick) and Dermacentor andersoni (Rocky Mountain wood tick) are widely spread throughout the United States, while only the latter predominates in Canada.

Mortality/Morbidity

In general, males, whites, and children are the groups mostly likely to be afflicted with Rocky Mountain spotted fever (RMSF). Although the incidence is lowest for the population older than 70 years, the case-fatality rate of 9% is the highest. It is lowest among adults aged 40-49 years at 0.6%. The overall annual case-fatality rate is 1.1-4.9%. Although it is a nationally surveyed illness, this number may be an underrepresentation because discrepancies exist between independent sources of RMSF mortality data. With appropriate treatment, the mortality rate ranges from 3-5%. Without treatment, and prior to the advent of tetracycline and chloramphenicol, the mortality rate was as high as 30%. If antibiotic therapy is delayed for more than 5 days from symptom onset, the case-fatality ratio is 3-4 times higher.

Race

Although whites are more likely to become affected with the disease, the mortality rate among African Americans is higher compared with whites. This may be due, in part, to the high percentage (22-66%) of dark-skinned individuals who do not experience a rash when infected with R rickettsii. The lack of a rash has been associated with mortality, possibly because of the delay in diagnosis and treatment. In addition, approximately 10% of American black males have from glucose-6-phosphate dehydrogenase deficiency, the presence of which has been linked to a more severe course of illness and fatality from RMSF.

Sex

Males have a higher incidence and higher rate of more severe disease compared with females.

Age

Children aged 5-9 years have the highest incidence in the United States. An estimated 3.3 cases per million occur in this age group, whereas only 1.4 cases per million occur in people older than 70 years.

Clinical

History

A detailed history eliciting information concerning recent travel, drug ingestion, animal exposure, ill contacts, occupation, and home environment are very important in identifying any disease that presents with fever and a rash. Specific details about the rash, if present, should include time and site of onset, rate and direction of spread, presence of pruritus, and relationship to fever.

  • Signs and symptoms of Rocky Mountain spotted fever (RMSF) occur 2-14 days after infection.
    • In 60-70% of patients with RMSF, the classic triad of fever (94%), headache (86%), and rash occurs 1-2 weeks post tick bite. Although the triad may not be present, headache, myalgias, and fever almost always occur and should alert the physician to the possibility of RMSF.
    • Approximately 15% of patients with RMSF may not report a history of a tick bite.
    • Less diagnostic symptoms include gastrointestinal disturbances (eg, nausea, vomiting, diarrhea, abdominal pain, anorexia), malaise, myalgias (83%), irritability, severe headache, and photophobia.

Physical

  • Vital signs and general appearance should be noted in all patients suspected of having Rocky Mountain spotted fever (RMSF).5
  • A fever greater than 102°F is usually present.
  • Approximately 84-91% of patients experience a rash 2-5 days after the onset of fever. Realizing that the absence of a rash does not exclude RMSF as the causative illness is important since cutaneous manifestations are not appreciated in 10-15% of patients.
    • In older patients and in severe or fatal cases of RMSF, the rash tends to appear later and with less frequency.
    • The rash initially consists of pink to bright red, discrete macules that are 1-5 mm in diameter. The macules blanch with pressure and may or may not be pruritic.
    • The lesions start on the wrists and the ankles then spread centripetally to cover the soles, and most importantly, the palms. The hands and the feet are both involved 49-74% of the time. The rash continues moving centrally to eventually involve the proximal extremities and the trunk. The face is usually spared. Involvement of the scrotum or the vulva is a diagnostic clue.


The palm of a patient with Rocky Mountain spotted...

The palm of a patient with Rocky Mountain spotted fever exhibiting the classic petechial rash associated with the disease. Courtesy of Sadhana Sathe, MD, PhD.

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The palm of a patient with Rocky Mountain spotted...

The palm of a patient with Rocky Mountain spotted fever exhibiting the classic petechial rash associated with the disease. Courtesy of Sadhana Sathe, MD, PhD.

    • Within days of presentation, the macules progress to papules and petechiae that may coalesce to form ecchymoses yielding the characteristic spotted appearance. The rash is most commonly macular followed by maculopapular; petechial; and less commonly, petechial-hemorrhagic.


The petechial rash of Rocky Mountain spotted feve...

The petechial rash of Rocky Mountain spotted fever affecting the sole and the dorsum of the patient's foot. Courtesy of Sadhana Sathe, MD, PhD.

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The petechial rash of Rocky Mountain spotted feve...

The petechial rash of Rocky Mountain spotted fever affecting the sole and the dorsum of the patient's foot. Courtesy of Sadhana Sathe, MD, PhD.

    • The involved areas may be tender and desquamate as the rash fades. The presence of an eschar is rare, as opposed to other rickettsial illnesses, but has been reported.
    • Other cutaneous abnormalities may include postinflammatory hyperpigmentation, jaundice, and mucosal ulcers. An erythema migrans–like rash has also been reported.
  • Other, less diagnostic, physical findings may include lymphadenopathy, hepatosplenomegaly, and signs of nuchal rigidity.
  • The clinical course of RMSF is more severe in individuals with a glucose-6-phosphate dehydrogenase enzyme deficiency. This likely contributes to the higher fatality rate seen in African Americans.

Causes

Rocky Mountain spotted fever (RMSF) is caused by the obligate intracellular pathogen, R rickettsii. See Pathophysiology.

More on Rocky Mountain Spotted Fever

Overview: Rocky Mountain Spotted Fever
Differential Diagnoses & Workup: Rocky Mountain Spotted Fever
Treatment & Medication: Rocky Mountain Spotted Fever
Follow-up: Rocky Mountain Spotted Fever
Multimedia: Rocky Mountain Spotted Fever
References
Further Reading
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Keywords

Rocky Mountain spotted fever, RMSF, Rickettsia rickettsii, R rickettsii, tick-borne diseases, rickettsioses, Amblyomma cajennense, A cajennense, Rhipicephalus sanguineous, R sanguineous, Dermacentor andersoni, D andersoni, tick fever, spotted fever

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Contributor Information and Disclosures

Author

Nicole L Lacz, MD, Chief Resident, Department of Radiology, St Barnabas Medical Center
Nicole L Lacz, MD is a member of the following medical societies: Alpha Omega Alpha, Phi Beta Kappa, and Sigma Xi
Disclosure: Nothing to disclose.

Coauthor(s)

Robert A Schwartz, MD, MPH, Professor and Head, Dermatology, Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health, UMDNJ-New Jersey Medical School
Robert A Schwartz, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Physicians, and Sigma Xi
Disclosure: Nothing to disclose.

Rajendra Kapila, MD, MBBS, Professor of Medicine, Department of Medicine, UMDNJ, New Jersey Medical School
Rajendra Kapila, MD, MBBS is a member of the following medical societies: American College of Physicians, American Medical Association, Infectious Diseases Society of America, and Infectious Diseases Society of New Jersey
Disclosure: Nothing to disclose.

Medical Editor

Noah S Scheinfeld, MD, JD, FAAD, Assistant Clinical Professor, Department of Dermatology, Columbia University; Consulting Staff, Department of Dermatology, St Luke's Roosevelt Hospital Center, Beth Israel Medical Center, New York Eye and Ear Infirmary; Private Practice
Noah S Scheinfeld, MD, JD, FAAD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Optigenex Consulting fee Independent contractor

Pharmacy Editor

David F Butler, MD, Professor of Dermatology, Texas A&M University College of Medicine; Chair, Department of Dermatology, Director, Dermatology Residency Training Program, Scott and White Clinic, Northside Clinic
David F Butler, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, American Society for Dermatologic Surgery, American Society for MOHS Surgery, Association of Military Dermatologists, and Phi Beta Kappa
Disclosure: Nothing to disclose.

Managing Editor

Jeffrey Meffert, MD, Assistant Clinical Professor of Dermatology, University of Texas Health Science Center-San Antonio
Jeffrey Meffert, MD is a member of the following medical societies: American Academy of Dermatology, American Medical Association, Association of Military Dermatologists, and Texas Dermatological Society
Disclosure: Nothing to disclose.

CME Editor

Joel M Gelfand, MD, MSCE, Medical Director, Clinical Studies Unit, Assistant Professor, Department of Dermatology, Associate Scholar, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania
Joel M Gelfand, MD, MSCE is a member of the following medical societies: Society for Investigative Dermatology
Disclosure: AMGEN Consulting fee Consulting; AMGEN Grant/research funds None; Genentech Consulting fee Consulting; Centocor Consulting fee Consulting; Centocor Grant/research funds None; Covance Consulting fee Consulting; Shire  Consulting

Chief Editor

Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center
Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.

 
 
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