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The Ehrlichioses
William Kwan
UNC Medicine-Pediatrics
Objectives
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Overview of 3 human Ehrlichioses
Microbiology
Epidemiology
Diagnosis
Treatment
Microbiology of Ehrlichiae
 Gram-negative obligate intracellular bacteria that grow in
vacuoles (morulae)
 Two Ehrlichiae species and Anaplasma cause three forms of
human Ehrlichioses
 Ehrlichia chaffeensis
 Ehrlichia ewingii
 Anaplasma phagocytophila
Human Monocytic Ehrlichiosis
(HME)
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Agent: Ehrlichia chaffeensis
Vector: Lone Star tick (and sometimes Dog tick)
Higher prevalence during late spring and early summer
Southeast, south central, and mid-Atlantic
Fever (97%), malaise (84%), headache (81%), myalgia (68%)
Diarrhea (25-68%), rash (36%, but only 6% at presentation),
confusion (20%)
 Complications: ARDS, meningoencephalitis, fulminant infection,
hemorrhage
 Mortality in 2-5%
 Leukopenia (60-74%), thrombocytopenia (72%), elevated LFT’s
(90%)
Human Monocytic Ehrlichiosis
(HME)
 Diagnosis based on clinical suspicion
 Most common diagnostic test: Serology using indirect
fluorescence antibody to E. chaffeensis
 Fourfold rise in titers between acute sera (on presentation)
and convalescent sera (drawn 2-4 weeks later)
 Single titer of 1:128 may be diagnostic but no established
threshold
Human Monocytic Ehrlichiosis
(HME)
 Peripheral blood smear or examination of buffy coat may show
rare morulae (1-20%)
Human Monocytic Ehrlichiosis
(HME)
 Peripheral blood smear or examination of buff coat may show
rare morulae (1-20%)
 PCR techniques being developed
 Immunochemical staining of tissue (e.g. lymph nodes, liver,
spleen, lung)
Human Monocytic Ehrlichiosis
(HME)
 Treatment of choice: Doxycycline 100mg bid x 10 days or up to
3-5 days following defervescence
 Alternative choice: Rifampin 300mg x 7-10 days
 Pregnancy:
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If disease not life-threatening: Rifampin
If disease life-threatening: Doxycycline
Human Granulocytic Anaplasmosis
(HGA)
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Formerly called Human Granylocytic Ehrlichiosis
Agent: Anaplasma phagocytophila
Vector: Deer tick
Higher prevalence during late spring and early summer
Northeast
Symptoms are very similar to those in HME
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Exception: Rash is very rare
 Leukopenia, thrombocytopenia, elevated LFT’s
 May have concurrent infection with Lyme Disease and much less
commonly Babesiosis
Human Granulocytic Anaplasmosis
(HGA)
 Initial diagnosis based on clinical suspicion
 Serology using IFA to A. phagocytophila
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Four-fold rise in titers between acute and convalescent sera
 Peripheral blood smear or buffy coat examination may show
morulae (20-80%, higher than for HME)
 PCR
 Immunochemical tissue staining
 Treatment is same as for HME: Doxycycline (or Rifampin)
Ehrlichiosis Ewingii
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Agent: E. ewingii
Vector: Lone Star tick
Higher prevalence during summer
Symptoms similar to HME but less severe
Usually diagnosed in immunocompromised
IFA utilizes E. chaffeensis antigen
No criteria for diagnostic serologies
Treat with Doxycycline
Take-Home Points
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HME and HGA are very similar diseases
HME more common in southeast, south central, mid-Atlantic
HGA more common in northeast
HGA may be accompanied by Lyme Disease
Treatment is Doxycycline 100mg bid x 7-10 days or up to 3-5
days after defervescence
 Rifampin may be used in pregnant patients with non-life
threatening disease
 Bacteria cartoons are corny
References
 Dumler et al., “Ehrlichioses in Humans: Epidemiology, Clinical
Presentation, Diagnosis, and Treatment.” The Journal of Clinical
Infectious Diseases. July 2007; 45: S45-51.
 Kasper et al., Harrison’s Principles of Internal Medicine. 16th ed.
New York: McGraw Hill, 2005.
 Sexton et al., “The Human Ehrlichioses.” UpToDate Online.
 Stone et al., “Human Monocytic Ehrlichiosis.” Journal of the
American Medical Association. November 10, 2004; 292: 2263 227.