Close
New

Medscape is available in 5 Language Editions – Choose your Edition here.

 

Ehrlichiosis

  • Author: Burke A Cunha, MD; Chief Editor: Michael Stuart Bronze, MD  more...
 
Updated: Sep 18, 2015
 

Background

Ehrlichiosis is an infection of white blood cells that affects various mammals, including mice, cattle, dogs, deer, horses, sheep, goats, and humans.[1, 2] (See the image below.)

Female Lone Star tick, Amblyomma americanum, found Female Lone Star tick, Amblyomma americanum, found in the southeastern and Midatlantic United States. It is a vector of several zoonotic diseases, including human monocytic ehrlichiosis and Rocky Mountain spotted fever. Courtesy of the CDC/Michael L. Levin, PhD.

Ehrlichia/Anaplasma are tiny (0.2-2 µm) obligate, intracytoplasmic, gram-negative organisms that resemble Rickettsia; divide by binary fission; and multiply within the cytoplasm of infected white blood cells. Clusters of Ehrlichia multiply in host monocyte vacuoles (phagosomes) to form large, mulberry-shaped aggregates called morulae. (See Etiology.)

Ehrlichia inclusion bodies, such as morulae, are visible in the cytoplasm of infected mononuclear phagocytic cells after 5-7 days. The type of ehrlichiosis that develops varies and depends on the infecting species and the type of leukocyte infected. Human granulocytic anaplasmosis (HGA), formerly known as human granulocytic ehrlichiosis (HGE), is caused by Anaplasma phagocytophilum, which infect granulocytes. In contrast, human monocytic ehrlichiosis (HME) is caused by Ehrlichia chaffeensis, which infects monocytes. (See Table, below.) (See Etiology.)

HGA and HME cause the same clinical manifestations. Therefore, the term ehrlichiosis is used for both types of infections. The total duration of illness for HME and HGA is unknown. No chronic cases have been reported at this time. (See History and Physical Examination.)

Table. Characteristics of HME Versus HGA (Open Table in a new window)

  Human monocytic ehrlichiosis (HME) Human granulocytic anaplasmosis (HGA)
Cell type Affected Monocytes Granulocytes
Organism E chaffeensis A phagocytophilum
Vector Amblyomma americanum (Lone Star tick) Ixodes scapularis (black-legged tick), Ixodes pacificus (Western black-legged tick) in California, Ixodes ricinus in Europe, and probably Ixodes persulcatus in parts of Asia
Location Southeastern and south-central United States Wisconsin and Minnesota, less active in New York and Connecticut, also California
Rash 30% of adults, 60% of children Rare
Prognosis ~3% mortality < 1% mortality

Complications of ehrlichiosis include the following:

  • Renal failure
  • Respiratory failure
  • Coagulopathy
  • Myocarditis
  • Encephalopathy
  • Coma

Because the tick vector and geographic range for HGA is the same as that for Lyme disease, rarely the 2 may coexist in the same patient; doxycycline is effective therapy for both. (See Treatment and Medication.)

In October 2008, a report was made of an apparent nosocomial infection with A phagocytophilum that was transmitted from blood donated by an infected woman who had spent time in Minnesota just prior to donating.

The major antigenic determinants of Ehrlichia are surface membrane proteins. These antigenic proteins are complex and consist of thermolabile and thermostable components. In terms of kilodalton (kd) molecular weight, the key protein bands associated with HME are the 27-, 29-, and 44-kd bands. The major antigenic determinants associated with HGA include the 40-, 44-, and 65-kd bands.

In 1999, Buller et al reported 4 incidents of ehrlichiosis in Missouri due to Ehrlichia ewingii.[3] The associated disease may be clinically indistinguishable from infection caused by E chaffeensis or A phagocytophilum; however, laboratory testing can distinguish these incidents from HGA and HME. (See Workup.)

Go to Tick Removal and Tick-Borne Diseases for complete information on these topics.

See 7 Bug Bites You Need to Know This Summer, a Critical Images slideshow, for helpful images and information on various bug bites.

Patient education

Educate patients in endemic ehrlichiosis areas to take proper precautions when traveling through wooded and/or tick-infested areas. (See Deterrence and Prevention.)

For patient education information, see Ticks.

Next

Etiology

Ehrlichia and Anaplasma species, members of the family Rickettsiae, are gram-negative, obligate, intracellular coccobacilli that resemble Rickettsia species. All 3 are forms of Alphaproteobacteria.

Like Rickettsia, Ehrlichia organisms gain access to the blood via a bite from an infected tick. A americanum (Lone Star tick, seen in the image below) is the principle tick vector of E chaffeensis and is the primary vector of human monocytic ehrlichiosis (HME). A phagocytophilum may be transmitted from Ixodes persulcatus ticks and possibly Dermacentor variabilis (dog tick/wood tick).

Female Lone Star tick, Amblyomma americanum, found Female Lone Star tick, Amblyomma americanum, found in the southeastern and Midatlantic United States. It is a vector of several zoonotic diseases, including human monocytic ehrlichiosis and Rocky Mountain spotted fever. Courtesy of the CDC/Michael L. Levin, PhD.

The primary target cell for HME is the macrophage, and the primary target for human granulocytic anaplasmosis (HGA) is the granulocyte. Intracellular infection is established within phagosomes, most often found in macrophages in the liver, spleen, lymph nodes, bone marrow, lung, kidney, and CNS.

HME and HGA are more severe in those with impaired splenic function.

Previous
Next

Epidemiology

Occurrence in the United States

The distribution of ehrlichiosis in the United States mirrors the tick distribution and appropriate mammalian vectors (eg, white-footed mouse, white-tailed deer). Ehrlichiosis occurs where mammalian hosts are in contact with the appropriate tick vector (ie, A americanum,D variabilis,Ixodes ticks). (See the maps below.)

Map of the United States showing the distribution Map of the United States showing the distribution of the Lone Star Tick, which is the principle vector for ehrlichiosis.
Established and reported distribution of anaplasmo Established and reported distribution of anaplasmosis vectors Ixodes scapularis and Ixodes pacificus, by county, in the United States from 1907-1996. Courtesy of the Division of Vector-Borne Infectious Diseases at the Centers for Disease Control and Prevention.

Most cases of ehrlichiosis in the United States occur in California and Texas and in the southeast and northeast regions of the country, with some cases occurring in the north-central states west of the Great Lakes.

Ehrlichiosis is a seasonal disease observed mainly from April to September. In 1999, ehrlichiosis became reportable to the US Centers for Disease Control and Prevention (CDC). In 2005, 786 cases of human granulocytic anaplasmosis (HGA) were reported. The 3 states that reported the most cases were New York (221 cases), Minnesota (186 cases), and Wisconsin (155 cases).[4, 5] In 2006, 646 cases of HGA were reported. The 3 states that reported the most cases were New York (235 cases), Minnesota (177 cases), and Wisconsin (49 cases).[6]

A 2011 study confirmed that B burgdorferi and A phagocytophilum share the same enzootic life cycle suggesting that it is important to monitor areas endemic for Lyme disease for HGA. In this study, La Crosse, WI is centrally located in a well-documented Lyme disease focus. HGA was identified by PCR in the blood of 53 patients with clinical findings consistent with HGA confirming that this region endemic for Lyme should now also be considered part of the upper Midwestern focus of endemnicity for HGA.[7]

In 2005, 506 cases of human monocytic ehrlichiosis (HME) were reported. The 3 states that reported the most cases were New York (85 cases), Oklahoma (79 cases), and New Jersey (64 cases). In 2006, 578 cases of HME were reported. The 3 states that reported the most cases were New York (141 cases), Missouri (73 cases), and New Jersey (67 cases).

A 2011 report identified a new ehrlichia species in 4 patients in the Minnesota and Wisconsin areas. All patients had the traditional clinical syndrome and responded to treatment. On testing, 17 of 697 Ixodes scapularis ticks collected in Minnesota or Wisconsin were positive for the same ehrlichia species by polymerase chain-reaction testing and genetic analyses revealed that this new ehrlichia species was closely related to E muris.[8]

International occurrence

Ehrlichiosis occurs essentially worldwide, and the frequency parallels the distribution of the appropriate tick vectors for the transmission of Ehrlichia bacteria and the mammalian hosts.[9]

Ehrlichia sennetsu causes a mononucleosis-like illness in Japan and Malaysia.

Sex-related demographics

The rates of HME and HGA are higher in males than in females, most likely due to a higher rate of participation in high-risk outdoor activities among males.

In 2006, the CDC reported that of the 646 cases of HGA, 357 were males and 273 were females (16 cases did not specify sex). HME had a similar distribution, with 337 males and 234 females among the 578 cases in 2006 (7 cases did not specify sex).

The incidence rates per 100,000 for males were 0.26 for HGA and 0.24 for HME. For females, the rates were 0.19 for HGA and 0.16 for HME.

Age-related demographics

Ehrlichiosis is reported more frequently in adults than in children. The highest age range is between 40 and 64 years. (See the graphs below.)

Anaplasmosis incidence by age. Courtesy of the Cen Anaplasmosis incidence by age. Courtesy of the Centers for Disease Control and Prevention.
Ehrlichiosis incidence by age. Courtesy of the Cen Ehrlichiosis incidence by age. Courtesy of the Centers for Disease Control and Prevention.
Previous
Next

Prognosis

Ehrlichiosis carries an excellent prognosis in healthy hosts. A favorable outcome is associated with the early use of antibiotics.[10]

The mortality rate for human monocytic ehrlichiosis (HME) is reported to be 2-5%, while that for HGA is 7-10%.

Elderly patients (>60 y) are more likely than others to develop severe infections and account for most deaths due to ehrlichiosis. In addition, ehrlichiosis may be severe in immunocompromised hosts, manifesting as a Rocky Mountain spotted fever (RMSF)–like illness that may be fatal. The great majority of cases of ehrlichiosis are asymptomatic. Most cases present as mild-to-moderate acute febrile illnesses, but some cases are severe/life threatening.

HME has a reported hospitalization rate as high as 60%, while that for HGA is 28-54%.

Previous
 
 
Contributor Information and Disclosures
Author

Burke A Cunha, MD Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital

Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, Infectious Diseases Society of America

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, Phi Beta Kappa

Disclosure: Received research grant from: Pfizer;GlaxoSmithKline;AstraZeneca;Merck;American Academy of Pediatrics<br/>Received income in an amount equal to or greater than $250 from: Sanofi Pasteur;Astra Zeneca;Novartis<br/>Consulting fees for: Sanofi Pasteur; Novartis; Merck; Astra Zeneca.

Samuel M Keim, MD, MS Professor and Chair, Department of Emergency Medicine, University of Arizona College of Medicine

Samuel M Keim, MD, MS is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, American Public Health Association, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Walid Abuhammour, MD, MBA, FAAP Professor of Pediatrics, Michigan State University College of Medicine; Director of Pediatric Infectious Disease, Department of Pediatrics, Al Jalila Children's Hospital

Walid Abuhammour, MD, MBA, FAAP is a member of the following medical societies: American Medical Association, Infectious Diseases Society of America, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Nicholas John Bennett, MBBCh, PhD, MA(Cantab), FAAP Assistant Professor of Pediatrics, Co-Director of Antimicrobial Stewardship, Medical Director, Division of Pediatric Infectious Diseases and Immunology, Connecticut Children's Medical Center

Nicholas John Bennett, MBBCh, PhD, MA(Cantab), FAAP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics

Disclosure: Received research grant from: Cubist Pharmaceuticals, Durata Therapeutics, and Biota Pharmaceutical<br/>Received income in an amount equal to or greater than $250 from: HealthyCT insurance<br/>Medico legal consulting for: Various.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Jon Mark Hirshon, MD, MPH, PhD Professor, Department of Emergency Medicine, University of Maryland School of Medicine

Jon Mark Hirshon, MD, MPH, PhD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Public Health Association, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Association, Oklahoma State Medical Association, Southern Society for Clinical Investigation, Association of Professors of Medicine, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

Thomas J Marrie, MD Dean of Faculty of Medicine, Dalhousie University Faculty of Medicine, Canada

Thomas J Marrie, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American Society for Microbiology, Association of Medical Microbiology and Infectious Disease Canada, Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Acknowledgements

Geofrey Nochimson, MD Consulting Staff, Department of Emergency Medicine, Sentara Careplex Hospital

Geofrey Nochimson, MD is a member of the following medical societies: American College of Emergency Physicians

Disclosure: Nothing to disclose.

References
  1. CDC. Ehrlichiosis. [Full Text].

  2. 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. 2006 Mar 31. 55:1-27. [Medline].

  3. Buller RS, Arens M, Hmiel SP, et al. Ehrlichia ewingii, a newly recognized agent of human ehrlichiosis. N Engl J Med. 1999 Jul 15. 341(3):148-55. [Medline].

  4. Aguero-Rosenfeld ME, Horowitz HW, Wormser GP, et al. Human granulocytic ehrlichiosis: a case series from a medical center in New York State. Ann Intern Med. 1996 Dec 1. 125(11):904-8. [Medline].

  5. Bakken JS, Dumler JS, Chen SM, et al. Human granulocytic ehrlichiosis in the upper Midwest United States. A new species emerging?. JAMA. 1994 Jul 20. 272(3):212-8. [Medline].

  6. Heilpern KL. Update: human ehrlichiosis--Maryland and Wisconsin, 1994. Ann Emerg Med. 1998 Jul. 32(1):108-10. [Medline].

  7. Lovrich SD, Jobe DA, Kowalski TJ, Policepatil SM, Callister SM. Expansion of the midwestern focus for human granulocytic anaplasmosis into the region surrounding la crosse, wisconsin. J Clin Microbiol. 2011 Nov. 49(11):3855-9. [Medline].

  8. Pritt BS, Sloan LM, Johnson DK, Munderloh UG, Paskewitz SM, McElroy KM, et al. Emergence of a new pathogenic Ehrlichia species, Wisconsin and Minnesota, 2009. N Engl J Med. 2011 Aug 4. 365(5):422-9. [Medline].

  9. Strle F. Human granulocytic ehrlichiosis in Europe. Int J Med Microbiol. 2004 Apr. 293 Suppl 37:27-35. [Medline].

  10. Hamburg BJ, Storch GA, Micek ST, Kollef MH. The importance of early treatment with doxycycline in human ehrlichiosis. Medicine (Baltimore). 2008 Mar. 87(2):53-60. [Medline].

  11. Everett ED, Evans KA, Henry RB, McDonald G. Human ehrlichiosis in adults after tick exposure. Diagnosis using polymerase chain reaction. Ann Intern Med. 1994 May 1. 120(9):730-5. [Medline].

  12. Cunha BA, Chandrankunnel JG, Hage JE. Ehrlichia chaffeensis human monocytic ehrlichiosis with pancytopenia. Scand J Infect Dis. 2012 Jun. 44(6):473-4. [Medline].

  13. Nayak SU, Simon GL. Myocarditis after trimethoprim/sulfamethoxazole treatment for ehrlichiosis. Emerg Infect Dis. 2013 Dec. 19(12):1975-7. [Medline]. [Full Text].

  14. Sachdev SH, Joshi V, Cox ER, Amoroso A, Palekar S. Severe life-threatening Ehrlichia chaffeensis infections transmitted through solid organ transplantation. Transpl Infect Dis. 2014 Feb. 16(1):119-24. [Medline].

  15. Schotthoefer AM, Meece JK, Fritsche TR. A clinical, diagnostic, and ecologic perspective on human anaplasmosis in the Upper Midwest. WMJ. 2014 Jun. 113(3):107-14; quiz 115. [Medline].

  16. St Clair K, Decker CF. Ehrlichioses: anaplasmosis and human ehrlichiosis. Dis Mon. 2012 Jun. 58(6):346-54. [Medline].

  17. Watson ME Jr, Storch GA, Dunne WM Jr, Burnham CA. A 2-year-old female with Fever and rash. J Clin Microbiol. 2011 Jul. 49(7):2389, 2784. [Medline]. [Full Text].

 
Previous
Next
 
Female Lone Star tick, Amblyomma americanum, found in the southeastern and Midatlantic United States. It is a vector of several zoonotic diseases, including human monocytic ehrlichiosis and Rocky Mountain spotted fever. Courtesy of the CDC/Michael L. Levin, PhD.
Map of the United States showing the distribution of the Lone Star Tick, which is the principle vector for ehrlichiosis.
Established and reported distribution of anaplasmosis vectors Ixodes scapularis and Ixodes pacificus, by county, in the United States from 1907-1996. Courtesy of the Division of Vector-Borne Infectious Diseases at the Centers for Disease Control and Prevention.
Anaplasmosis incidence by age. Courtesy of the Centers for Disease Control and Prevention.
Ehrlichiosis incidence by age. Courtesy of the Centers for Disease Control and Prevention.
Table. Characteristics of HME Versus HGA
  Human monocytic ehrlichiosis (HME) Human granulocytic anaplasmosis (HGA)
Cell type Affected Monocytes Granulocytes
Organism E chaffeensis A phagocytophilum
Vector Amblyomma americanum (Lone Star tick) Ixodes scapularis (black-legged tick), Ixodes pacificus (Western black-legged tick) in California, Ixodes ricinus in Europe, and probably Ixodes persulcatus in parts of Asia
Location Southeastern and south-central United States Wisconsin and Minnesota, less active in New York and Connecticut, also California
Rash 30% of adults, 60% of children Rare
Prognosis ~3% mortality < 1% mortality
Previous
Next
 
 
 
 
 
All material on this website is protected by copyright, Copyright © 1994-2016 by WebMD LLC. This website also contains material copyrighted by 3rd parties.