eMedicine Specialties > Pediatrics: General Medicine > Infectious Disease

Rocky Mountain Spotted Fever

Author: Nicholas John Bennett, MB, BCh, PhD, Fellow in Pediatric Infectious Disease, Department of Pediatrics, State University of New York Upstate Medical University
Coauthor(s): Joseph Domachowske, MD, Professor of Pediatrics, Microbiology and Immunology, Department of Pediatrics, Division of Infectious Diseases, State University of New York-Upstate Medical University; Walid Abuhammour, MD, FAAP, Associate Professor of Pediatrics, Michigan State University; Director of Pediatric Infectious Disease, Department of Pediatrics, Hurley Medical Center
Contributor Information and Disclosures

Updated: Sep 10, 2009

Introduction

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Background

Rocky Mountain spotted fever (RMSF) is the most common rickettsial infection and the second most commonly reported tick-borne disease (after Lyme disease) in the United States.

The causative agent is Rickettsia rickettsii (named after Howard T. Ricketts, the discoverer of the organism), an Alphaproteobacteria and member of the spotted fever groups of rickettsial infections. Rocky Mountain spotted fever was first described in the late 1800s in the Bitterroot Valley of Idaho. For several decades, it was thought to be limited to the Rocky Mountain area; however, it now has a high documented prevalence in the eastern United States. The bacteria is spread mainly through the bites of infected ticks; the dog tick, wood tick and Lone Star tick are all potential carriers and are responsible for Rocky Mountain spotted fever in different parts of the United States.

The disease was so problematic because of its mortality of up to 30% that the Rocky Mountain Laboratory was established in Hamilton, Montana to help investigate it. This laboratory is now part of the National Institute of Allergy and Infectious Diseases (NIAID). Rocky Mountain spotted fever has the highest mortality of any tick-borne illness in the United States.

Rocky Mountain spotted fever is a reportable disease in the United States.

Pathophysiology

Rocky Mountain spotted fever is a diffuse small-vessel vasculitis. R rickettsii is a small, gram-negative, obligate intracellular coccobacillus with a tropism for human endothelial cells. This bacterium causes membrane disruption and increased permeability.

Rickettsiae can be demonstrated in the cytoplasm and the nucleus of cells. Possible mechanisms for cellular injury include injury to the cell membrane, depletion of adenosine 5-triphosphate (which leads to failure of the sodium pump), and damage to the cell caused by toxic products of rickettsial metabolism.

Vascular lesions are responsible for the clinical manifestations, including rash, headache, alteration in the level of consciousness, heart failure, and shock. Vascular lesions can be found everywhere, with highest predilection for the skin, gonads, and adrenal glands. Profound hyponatremia is common. Several mechanisms have been postulated, including (1) a shift in water from the intracellular spaces to the extracellular spaces, (2) increased loss of sodium in the urine, and (3) an exchange of sodium for potassium at the cellular level.

Edema of the medulla oblongata may contribute to fatality in some patients.

Concentrations of antidiuretic hormone and aldosterone are increased in some patients.

Frequency

United States

Rocky Mountain spotted fever has been reported in almost every state in the continental United States, with an age-related annual incidence of 0.5-3 cases per million population. In 1997-2002, the mean incidence of was 2.2 cases per million per year.1

States reporting the highest rate of disease include North Carolina, South Carolina, Tennessee, Oklahoma, and Arkansas; these states accounted for more than half the total cases in recent years. The term Rocky Mountain spotted fever is a misnomer because it is relatively rare in the Rocky Mountain states. About 90% of cases occur between April and September, the time of the year when ticks have maximal activity and when people participate in outdoor recreational activities. See Media file 1.

Annual incidence per million population for Rocky...

Annual incidence per million population for Rocky Mountain spotted fever by state in the United States for 2002, as determined on the basis of cases reported to the National Electronic Telecommunications System for Surveillance. Image courtesy of the Centers for Disease Control and Prevention.

Annual incidence per million population for Rocky...

Annual incidence per million population for Rocky Mountain spotted fever by state in the United States for 2002, as determined on the basis of cases reported to the National Electronic Telecommunications System for Surveillance. Image courtesy of the Centers for Disease Control and Prevention.

International

The disease is also found in Canada, Mexico, Central America, and South America. However, the arthropod vector differs by location (see the table below). Other illnesses similar to Rocky Mountain spotted fever are also found worldwide.

Human Disease Around the World Caused by Spotted Fever Group Rickettsiae.

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Table
OrganismDisease or PresentationGeographic Location
R rickettsiiRocky Mountain spotted feverNorth, Central and South America
Rickettsia conoriiMediterranean spotted fever, boutonneuse fever, Israeli spotted fever, Astrakhan fever, Indian tick typhusEurope, Asia, Africa, India, Israel, Sicily, Russia, Europe, Asia, Africa, India, Israel, Sicily, Russia
Rickettsia akariRickettsialpoxWorldwide
Rickettsia sibiricaSiberian tick typhus, North Asian tick typhusSiberia, People's Republic of China, Mongolia, Europe
Rickettsia australisQueensland tick typhusAustralia
Rickettsia honeiFlinders Island spotted fever, Thai tick typhusAustralia, South Eastern Asia
Rickettsia africaeAfrican tick-bite feverSub Saharan Africa, Caribbean
Rickettsia japonicaJapanese or Oriental spotted feverJapan
Rickettsia felisCat flea rickettsiosis, flea borne typhusWorldwide
Rickettsia slovacaNecrosis, erythema, lymphadenopathyEurope
Rickettsia heilongjaiangensisMild spotted feverChina, Asian region of Russia
Rickettsia parkeriMild spotted feverUS
OrganismDisease or PresentationGeographic Location
R rickettsiiRocky Mountain spotted feverNorth, Central and South America
Rickettsia conoriiMediterranean spotted fever, boutonneuse fever, Israeli spotted fever, Astrakhan fever, Indian tick typhusEurope, Asia, Africa, India, Israel, Sicily, Russia, Europe, Asia, Africa, India, Israel, Sicily, Russia
Rickettsia akariRickettsialpoxWorldwide
Rickettsia sibiricaSiberian tick typhus, North Asian tick typhusSiberia, People's Republic of China, Mongolia, Europe
Rickettsia australisQueensland tick typhusAustralia
Rickettsia honeiFlinders Island spotted fever, Thai tick typhusAustralia, South Eastern Asia
Rickettsia africaeAfrican tick-bite feverSub Saharan Africa, Caribbean
Rickettsia japonicaJapanese or Oriental spotted feverJapan
Rickettsia felisCat flea rickettsiosis, flea borne typhusWorldwide
Rickettsia slovacaNecrosis, erythema, lymphadenopathyEurope
Rickettsia heilongjaiangensisMild spotted feverChina, Asian region of Russia
Rickettsia parkeriMild spotted feverUS


Mortality/Morbidity

The mortality rate during the preantibiotic era was as high as 30%; however, the mortality rate now ranges from approximately 2% in children to 9% in elderly persons. The case-fatality rate is higher (6.2%) for persons whose treatment begins more than 3 days after onset of symptoms than for those treated within the first 3 days of illness (1.3%). Patients with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency tend to have a severe course of Rocky Mountain spotted fever.

Race

People of African descent have reportedly had a high mortality rate partly due to the 12% rate of G-6-PD deficiency in male blacks. Rocky Mountain spotted fever may also be diagnosed later in blacks than in others because of the difficulty in detecting the early macular rash.

Prior to 2000, American Indians had similar rates of Rocky Mountain spotted fever to other races in the United States.2  From 2001-2005, rates increased disproportionately (16.8 cases per million vs 0.5-4.2 cases per million for other races). The highest rates were in Oklahoma (113.1 cases per million).3

Sex

The incidence is higher in male individuals than in female individuals, with a male-to-female ratio of 1.7:1.

Age

Children are at greater risk of acquiring Rocky Mountain spotted fever than are adults. The highest incidence occurs in children aged 5-9 years. However, the highest mortality is in those aged 50 years or older.

Clinical

History

  • The incubation period for Rocky Mountain spotted fever (RMSF) is 2-8 days after the tick bite.
  • History of tick bite is only present in two thirds of cases.
  • Symptoms can begin gradually or abruptly.
  • Fever, headache, rash, toxicity, myalgia, and mental confusion are the major clinical manifestations.
    • The patient's body temperature is usually higher than 38.8°C (101.8°F)
    • Headache is the most common neurologic manifestation. In older children and adults, the headache may be intractable and may be ongoing day and night. Young children may not complain of headache.
    • Nausea, vomiting, and abdominal pain may occur.
    • Conjunctival hyperemia and photophobia may be observed.
  • The rash of Rocky Mountain spotted fever is an important pathognomonic feature of the disease and is present in 80-90% of patients.
    • Rash begins as blanching maculopapular lesions. These lesions become petechial or purpuric in approximately one half of patients, accounting for its former name of black measles.
    • The rash first appears peripherally on the wrists and ankles. It spreads centripetally over the next 2-3 days.
    • Involvement of the palms and soles is an important diagnostic feature.
    • In most patients, rash usually appears by the second or third day. However, it may be delayed until the sixth day.
    • Early recognition of the blanching macular eruption is vital, because the classic petechial rash does not typically appear until 6 days or so after the initial symptoms become apparent.

Physical

Physical signs vary and include the following:

  • Body temperature is higher than 38.8°C (101.8°F).
  • Patient might have a toxic appearance.
  • A characteristic skin rash appears. It may be absent in 10-20% of infected individuals.
  • Hepatomegaly and splenomegaly are present in approximately 33% of patients.
  • Signs of meningoencephalitis include restlessness, irritability, mental confusion, and delirium.
  • Meningismus may occur. Findings may include neck stiffness, photophobia, a positive Kernig sign (pain on knee extension when hips flexed to 90°), and a positive Brudzinski sign (knee and hip flexion when the is neck flexed).
  • Ataxia may be present.
  • Spastic paralysis may occur.
  • Sixth nerve palsy may be observed.
  • Muscle tenderness is a common feature.

Causes

Ticks are the natural hosts, reservoirs, and vectors of R rickettsii. The species of tick acting as the vector varies by geographic location. R rickettsii is transmitted to humans by the bite of an infected tick. Adult ticks transmit the disease to humans during feeding. At least 6 hours of tick attachment is needed for the transmission of R rickettsii.

  • Primary hosts of R rickettsii
    • Dermacentor variabilis (dog tick) in the eastern United States and eastern Canada
    • Dermacentor andersoni (wood tick) in the western United States and western Canada
    • Amblyomma americanum (Lone Star tick) in the southwestern United States
  • Transmissions
    • Humans usually acquire infection through the bite of an infected tick.
    • On occasion, transmission occurs by scratching or rubbing infectious tick feces into the skin.
    • Laboratory personnel can be infected by inoculation or inhalation of aerosolized infectious specimens. For this reason, only specially equipped laboratories should attempt to culture and isolate Rickettsia species. Detection by other means (eg, serology) is more readily available than culture and isolation.

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

References

  1. Chapman AS, Bakken JS, Folk SM, et al. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis--United States: a practical guide for physicians and other health-care and public health professionals. MMWR Recomm Rep. Mar 31 2006;55(RR-4):1-27. [Medline][Full Text].

  2. Holman RC, McQuiston JH, Haberling DL, Cheek JE. Increasing incidence of Rocky Mountain spotted fever among the American Indian population in the United States. Am J Trop Med Hyg. Apr 2009;80(4):601-5. [Medline].

  3. Adjemian JZ, Krebs J, Mandel E, McQuiston J. Spatial clustering by disease severity among reported Rocky Mountain spotted fever cases in the United States, 2001-2005. Am J Trop Med Hyg. Jan 2009;80(1):72-7. [Medline].

  4. [Guideline] Chapman AS, Bakken JS, Folk SM, et al. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis--United States: a practical guide for physicians and other health-care and public health professionals. MMWR Recomm Rep. Mar 31 2006;55:1-27. [Medline][Full Text].

  5. Cale DF, McCarthy MW. Treatment of Rocky Mountain spotted fever in children. Ann Pharmacother. Apr 1997;31(4):492-4. [Medline].

  6. Abramson JS, Givner LB. Rocky Mountain spotted fever. Pediatr Infect Dis J. Jun 1999;18(6):539-40. [Medline].

  7. American Academy of Pediatrics Committee on Infectious Diseases. Rocky Mountain spotted fever. In: Red Book. 27th Ed. Elk Grove Village, IL: AAP; 2006:570-2.

  8. Azad AF, Beard CB. Rickettsial pathogens and their arthropod vectors. Emerg Infect Dis. Apr-Jun 1998;4(2):179-86. [Medline].

  9. Kostman JR. Laboratory diagnosis of rickettsial diseases. Clin Dermatol. May-Jun 1996;14(3):301-6. [Medline].

  10. Thorner AR, Walker DH, Petri WA. Rocky mountain spotted fever. Clin Infect Dis. Dec 1998;27(6):1353-9; quiz 1360. [Medline].

Further Reading

Keywords

Rocky Mountain spotted fever, RMSF, tick-borne disease, Rickettsia rickettsii, R rickettsii, black measles, Lyme disease, vasculitis, edema of the medulla oblongata, rickettsial disease, glucose-6-phosphate dehydrogenase, G-6-PD deficiency, conjunctival hyperemia, photophobia, hepatomegaly, splenomegaly, meningoencephalitis, meningismus

Contributor Information and Disclosures

Author

Nicholas John Bennett, MB, BCh, PhD, Fellow in Pediatric Infectious Disease, Department of Pediatrics, State University of New York Upstate Medical University
Nicholas John Bennett, MB, BCh, PhD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Pediatrics
Disclosure: Nothing to disclose.

Coauthor(s)

Joseph Domachowske, MD, Professor of Pediatrics, Microbiology and Immunology, Department of Pediatrics, Division of Infectious Diseases, State University of New York-Upstate Medical University
Joseph Domachowske, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, and Phi Beta Kappa
Disclosure: Nothing to disclose.

Walid Abuhammour, MD, FAAP, Associate Professor of Pediatrics, Michigan State University; Director of Pediatric Infectious Disease, Department of Pediatrics, Hurley Medical Center
Walid Abuhammour, MD, FAAP is a member of the following medical societies: American Medical Association and Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.

Medical Editor

José Rafael Romero, MD, Director of Pediatric Infectious Diseases Fellowship Program, Associate Professor, Department of Pediatrics, Combined Division of Pediatric Infectious Diseases, Creighton University/University of Nebraska Medical Center
José Rafael Romero, MD is a member of the following medical societies: American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, New York Academy of Sciences, and Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from financial planner; Avanir Pharma Stock Investment from financial planner ; WebMD Salary and stock Employment and investment from financial planner

Managing Editor

Larry I Lutwick, MD, Professor of Medicine, State University of New York, Downstate Medical School; Director, Infectious Diseases, Veterans Affairs New York Harbor Health Care System, Brooklyn Campus
Larry I Lutwick, MD is a member of the following medical societies: American College of Physicians and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

CME Editor

Robert W Tolan Jr, MD, Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine
Robert W Tolan Jr, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, Phi Beta Kappa, and Physicians for Social Responsibility
Disclosure: GlaxoSmithKline Honoraria Speaking and teaching; MedImmune Honoraria Speaking and teaching; Merck Honoraria Speaking and teaching; sanofi pasteur Honoraria Speaking and teaching; Baxter Healthcare Honoraria Speaking and teaching

Chief Editor

Russell W Steele, MD, Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine
Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, and Southern Medical Association
Disclosure: None None None

 
 
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