Clinical Background
Human ehrlichiosis is an arthropod-transmitted infection.
Epidemiology
- Incidence - 1.7/1,000,000 in U.S.
- Age - more common in persons >60 years
- Sex - male predominance
- Transmission - Ixodes tick
- Peak infectious season is April through September
- Infection rate is highest in Southeastern and mid-Atlantic states
Organism
- Ehrlichiae are small, obligate intracellular bacteria with gram-negative staining walls
- Human disease
- E. chaffeensis (human monocytotropic ehrlichiosis, HME)
- Transmitted by lone star tick (Amblyomma americanum)
- Major reservoir is in white-tailed deer
- E . ewingii (human ewingii ehrlichiosis)
- A. phagocytophilum - formerly called human granlocytotropic ehrlichiosis (HGE), but now known as human granulocytic anaplasmosis (HGA)
Clinical Presentation
- HGA and HME infections are clinically indistinguishable
- Fever, headache and malaise within 1 month after exposure
- Acute infection - progressive leukopenia (often with a left shift), thrombocytopenia and anemia
- Elderly and immunocompromised patients more prone to severe infections and death
Treatment
- Antibiotic therapy should be started as soon as possible after onset of symptoms
- Nonspecific clinical presentation and high fatality rate if HME untreated
- Serological diagnosis confirmation may take several weeks as convalescent titers are necessary
Prevention
- Avoidance of tick bites by wearing clothing leaving only minimal skin exposed
- Prompt removal of ticks
See Also
Diagnosis
Diagnosis
- Laboratory testing
- E. chaffeensis antibody testing by IFA and/or PCR
- Other laboratory findings - mild-to-moderate elevations of aspartate and alanine aminotransferases, alkaline phosphatase and lactate dehydrogenase
- Peripheral blood smears (Wrights stained)
- Morulae are rarely seen
- Intracytoplasmic inclusions
- <10% in HME
- 25-75% in HGA in 18+ week of infection
Differential Diagnosis
- Babesia
- Lyme disease
- Rickettsial disease
- Francisella
- Brucellosis
Tests generally appear in the order most useful for common clinical situations
| Test name: Ehrlichia chaffeensis Antibodies, IgG & IgM by IFA
|
| ARUP #: 0051002 |
| Methodology: Indirect Fluorescent Antibody
|
| Use: Use acute and convalescent samples to determine if infection is due to E. chaffeensis |
| Limitations: Because low levels of IgM antibodies may occasionally persist for more than 12 months post-infection, a single IgM result should be interpreted with caution |
| Follow-up:
|
| Test name: Wright's Stain
|
| ARUP #: 0049176 |
| Methodology: Stain/Microscopic
|
| Use: Confirm presence of Babesia |
Additional Tests Available
| Test name: Ehrlichia chaffeensis Antibody, IgG by IFA
|
| ARUP #: 0051004 |
| Methodology: Indirect Fluorescent Antibody
|
| Comments: |
| Test name: Ehrlichia chaffeensis Antibody, IgM by IFA
|
| ARUP #: 0051003 |
| Methodology: Indirect Fluorescent Antibody
|
| Comments: |
References
General References
Bakken JS, Dumler JS. Clinical diagnosis and treatment of human granulocytotropic anaplasmosis. Ann N Y Acad Sci.
2006;
1078:
236-247.
Dumler JS, Madigan JE, Pusterla N, Bakken JS. Ehrlichioses in humans: epidemiology, clinical presentation, diagnosis, and treatment. Clin Infect Dis.
2007;
45 Suppl 1:
S45-S51.
Dumler JS. Anaplasma and Ehrlichia infection. Ann N Y Acad Sci.
2005;
1063:
361-373.
Dumler JS. Molecular methods for ehrlichiosis and Lyme disease. Clin Lab Med.
2003;
23(
4):
867-84, vi.
Openshaw JJ, Swerdlow DL. Human ehrlichiosis: clinical and ecological challenges. South Med J.
2007;
100(
8):
769-770.
Stone JH, Dierberg K, Aram G, Dumler JS. Human monocytic ehrlichiosis. JAMA.
2004;
292(
18):
2263-2270.
Medical Reviewers
Litwin, Christine, M.D. Medical Director, Immunology at ARUP Laboratories; Professor, Clinical Pathology, University of Utah
Comprehensive Review: July 2008
Last Update: July 2008
