Emerging Tick-Borne Illnesses: Ehrlichiosis

Epidemiology

Incidence:

Overall annual incidence noted to be 3.2 cases per million in the United States between 2008 and 2012 (Biggs 2016)
Highest incidence occurs in those 60-69 years of age (Biggs 2016)

Age:

Median age is 55 years of age with 64% of cases reported in Caucasian patients (Heitman 2016)

Gender:

Morbidity/Mortality:

Case fatality rate is estimated to be 0.7-1% overall (Heitman 2016).
- Case fatality rate is highest in those over under 5 years of age and over 70 years of age

Geography and Seasonality (Heitman 2016): Cases most frequently reported in the Southeastern and Southcentral United States

Poor Prognostic Factors (Biggs 2016):

After tick transmissibility, chaffennis, an obligate intracellular bacterial, has a predilection for monocytes and tissue macrophages, specifically neutrophils
Once infected, the organism multiplies within cytoplasmic membrane-bound vacuoles forming clusters of bacterial called morulae
Infection elicits a systemic inflammatory response with multiorgan involvement, particularly the spleen, lymphatic system, and bone marrow

Symptoms (Biggs 2016):

Symptoms typically appear 5-14 days after bite of an infected tick
Rash is present more often than Anaplasmosis
- Present in up to 1/3^rd of patients
- Typically occurs 5 days after illness onset
Fever occurs in 96% of recognized cases of ehrlichiosis along with other non-specific flu-like symptoms:
- Headache
- Malaise
- Myalgias
Gastrointestinal symptoms are often seen unlike Anaplasmosis
- Very commonly seen in children
Respiratory symptoms or Cough is present in approximately 28% of patients
Central Nervous System involvement is present in approximately 20% of patients
- Meningitis and Meningoencephalitis
Severe Manifestations: Most cases are self-limiting, but Ehrlichiosis has been associated with the following severe disease manifestations:
- Shock
- Renal Failure
- Hepatic Failure
- Coagulopathy
- Hemorrhagic Manifestations
- Hemophagocytic Syndromes
- ARDS

Labs: Characteristic laboratory findings are seen in Ehrlichiosis along fever and non-specific flu-like illness:

Blood Smear:

May see morulae with microscopic examination of blood smears but blood smear may be relatively insensitive and inconsistent and is dependent on operator experience (Biggs 2016)
Observation of morulae is seen much less commonly than in Anaplasmosis

Confirmatory Testing:

Serological testing of IgM and IgG antibodies using indirect immunofluorescence assay (IFA) is available for diagnosis
RT-PCR assays is available for diagnosis and is most sensitive during the first week of illness and is the test of choice
Immunohistochemical staining of skin, tissue, or bone marrow biopsies has also been used for diagnosis

Guest Post By:

Akash Ray, DO
PGY-2 Emergency Medicine Resident Inspira Medical Center
Vineland, NJ
Twitter: @_kashray

Biggs H et al. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis – United States. MMWR Recomm Rep. 2016. PMID: 27172113
Heitman N at al. Increasing Incidence of Ehrlichiosis in the United States: A Summary of National Surveillance of Ehrlichia chaffeensis and Ehrlichia ewingii Infections in the United States, 2008-2012. Am J Trop Med Hyg. 2016. PMID: 26621561

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)