2. William Kwan UNC Medicine-Pediatrics
The Ehrlichioses
William Kwan
UNC Medicine-Pediatrics

3. Objectives Overview of 3 human Ehrlichioses Microbiology Epidemiology
Diagnosis
Treatment

4. 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

5. Human Monocytic Ehrlichiosis (HME)
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%)

6. 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

7. Human Monocytic Ehrlichiosis (HME)
Peripheral blood smear or examination of buffy coat may show rare morulae (1-20%)

9. 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)

10. 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:
If disease not life-threatening: Rifampin
If disease life-threatening: Doxycycline

12. Human Granulocytic Anaplasmosis (HGA)
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
Exception: Rash is very rare
Leukopenia, thrombocytopenia, elevated LFT’s
May have concurrent infection with Lyme Disease and much less commonly Babesiosis

13. Human Granulocytic Anaplasmosis (HGA)
Initial diagnosis based on clinical suspicion
Serology using IFA to A. phagocytophila
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)

14. Ehrlichiosis Ewingii 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

16. Take-Home Points 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

17. 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: