Ehrlichiosis

Ehrlichiosis
ICD-10	A79.8
ICD-9	082.4
DiseasesDB	31663
MedlinePlus	001381
MeSH	D016873

This page is about clinical aspects of the disease.  For microbiologic aspects of the causative organism(s), see Ehrlichia.

Ehrlichiosis Microchapters
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Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Ehrlichiosis from other Diseases
Epidemiology and Demographics
Risk Factors
Natural History, Complications and Prognosis
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Prevention
Case Studies
Case #1
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Raviteja Guddeti, M.B.B.S. [2]

Synonyms and keywords: Sennetsu fever; human granulocytic ehrlichiosis; Anaplasma phagocytophilum; Ehrlichia phagocytophila; human monocytic ehrlichiosis

Diagnosis

History and Symptoms | Physical Examination | Laboratory Findings | Other Imaging Findings | Other Diagnostic Studies

Treatment

Medical Therapy | Surgery | Primary Prevention | Secondary Prevention | Future or Investigational Therapies

Case Studies

Case#1

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Pathophysiology

• Ehrlichia are transported between cells through the host cell filopodia during initial stages of infection, whereas, in the final stages of infection the pathogen ruptures the host cell membrane.
• Most of the symptoms of Ehrlichiosis can likely be ascribed to the immune dysregulation that it causes.
• Early in infection, production of TNF-alpha, a cellular product that promotes inflammation and immune response, is suppressed. Experiments in mouse models further supports this hypothesis, as mice lacking TNF-alpha I/II receptors are resistant to liver injury caused by ehrlichia infection.
• Late in infection, however, production of this substance can be upregulated by 30 fold, which is likely responsible for the "toxic shock-like" syndrome seen in some severe cases of ehrlichiosis.

Causes

Five species of the genus Ehrlichia have been shown to cause human infection:

• Anaplasma phagocytophilum (which causes human granulocytic anaplasmosis, formerly known as human granulocytic ehrlichiosis).
• Ehrlichia ewingii (which causes human ewingii ehrlichiosis). E. ewingii primarily infects deer and dogs (see Ehrlichiosis (canine)).
• Ehrlichia chaffeensis (which causes human monocytic ehrlichiosis).
• Ehrlichia canis
• Neorickettsia sennetsu

The latter two infections are not well studied.

Epidemiology and Demographics

• The average reported annual incidence is 0.7 cases per million population.
• A. phagocytophilium is endemic to New England and the north central and Pacific regions of the United States.
• E. chaffeensis is most common in the south central and southeastern states.
• E. ewingii is most common in the south central and southeastern states.

The lone star tick (Amblyomma americanum) is the primary vector of both Ehrlichia chaffeensis and Ehrlichia ewingii in the United States .

Risk Factors

Risk factors for ehrlichiosis include:

• Living near an area with a lot of ticks
• Owning a pet that may bring a tick home
• Walking or playing in high grasses

Natural History, Complications and Prognosis

Complications

• Respiratory distress syndrome
• Hepatitis
• Kidney damage
• Lung damage
• Other organ damage
• Seizure
• Candidiasis
• Opportunistic nosocomial infections
• Death

Diagnosis

Symptoms

• Chills
• Fever
• Headache
• Nausea
• Muscle aches / myalgias
• Fatigue

Other possible symptoms include:

• Diarrhea
• Fine pinhead-sized areas of bleeding in the skin (petechial rash)
• Flat red rash (maculopapular rash)
• General ill feeling (malaise)

A rash appears in fewer than half of cases.

Physical Examination

Vitals

• Elevated body temperature
• Increased heart rate
• Blood pressure

Skin

• Rash
• Purpura - can be a presenting feature.

Head

• Swollen lymph nodes

Laboratory Findings

• Complete blood count (CBC)
• Granulocyte stain
• Fluorescent antibody test

Treatment

• Doxycycline is the drug of choice.
• For people allergic to drugs of the tetracycline class, rifampicin is an alternative.

• Early clinical experience suggested that chloramphenicol may also be effective, however in vitro susceptibility testing revealed resistance.

Antimicrobial regimen

• 1. Human Monocytic Ehrlichiosis or Human Granulocytic Anaplasmosis (adult)

• Preferred regimen: Doxycycline 100 mg PO/IV q12h for 7-14 days
• Note: Patients should be treated for at least 3 days after the fever subsides and until there is evidence of clinical improvement
• Alternative regimen (1): Chloramphenicol 500mg PO qid

• Alternative regimen (2): Rifampin 600 mg PO/IV qd for 7-10 days

• 2. Human Monocytic Ehrlichiosis or Human Granulocytic Anaplasmosis (pediatric)

• 2.1 ≥ 8 years old

• Preferred regimen: Doxycycline 2 mg/kg IV/PO q12h (Maximum, 200 mg/day) for 10 days

• 2.2 < 8 years old without Lyme disease

• Preferred regimen: Doxycycline 2 mg/kg IV/PO q12h (Maximum, 200 mg/day) for 4-5 days (or 3 days after resolution of fever)

• 2.3 co-infected with Lyme disease

• Preferred regimen: Doxycycline, then Amoxicillin 50 mg/kg in 3 divided doses (Maximum, 500 mg/dose) OR Cefuroxime 30 mg/kg in 2 divided doses (Maximum, 500 mg/dose) for 14 days

References

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