Ehrlichiosis: Definition and Treatment
Ehrlichiosis is a tick-borne bacterial infection requiring prompt treatment with doxycycline for all patients regardless of age, including children under 8 years. 1
What is Ehrlichiosis?
Ehrlichiosis is a tick-borne disease caused by obligate intracellular bacteria in the genus Ehrlichia that infect white blood cells. There are several forms of human ehrlichiosis in the United States:
- Human Monocytic Ehrlichiosis (HME): Caused by Ehrlichia chaffeensis, which primarily infects monocytes and tissue macrophages
- Human Ewingii Ehrlichiosis: Caused by Ehrlichia ewingii
- Human Granulocytic Anaplasmosis (HGA): Caused by Anaplasma phagocytophilum, which infects neutrophils
Clinical Presentation
Symptoms typically appear 5-14 days after an infected tick bite 1 and include:
- Fever (96% of cases)
- Headache (72%)
- Malaise (77%)
- Myalgia (68%)
- Gastrointestinal symptoms: nausea (57%), vomiting (47%), diarrhea (25%)
- Rash (occurs in approximately one-third of patients, more common in children)
- Respiratory symptoms (28%, more common in adults)
Severe manifestations can include:
- Meningitis or meningoencephalitis (20% of patients)
- Acute respiratory distress syndrome (ARDS)
- Toxic shock-like syndrome
- Renal or hepatic failure
- Coagulopathies
Laboratory Findings
Common laboratory abnormalities include:
- Leukopenia (decreased white blood cells)
- Thrombocytopenia (decreased platelets)
- Elevated liver enzymes (transaminases)
- Hyponatremia
Treatment of Ehrlichiosis
First-Line Treatment
Doxycycline is the drug of choice for all patients with ehrlichiosis, regardless of age. 1
- Adults: 100 mg twice daily (orally or intravenously)
- Children <45.4 kg: 2.2 mg/kg body weight twice daily (orally or intravenously)
- Duration: Treat for at least 3 days after fever subsides and until clinical improvement is noted, typically a minimum of 5-7 days total
Early treatment is critical as delay can lead to severe disease and death. Children under 5 years have higher mortality rates when treatment is delayed 1.
Response to Treatment
Fever typically resolves within 24-48 hours after starting doxycycline. If a patient fails to respond within 48 hours, reconsider the diagnosis 1.
Important Note on Doxycycline Use in Children
The American Academy of Pediatrics and CDC explicitly recommend doxycycline as the treatment of choice for ehrlichiosis in patients of all ages, including children under 8 years 1, 2. Short courses of doxycycline do not pose a substantial risk for tooth staining in children 1.
Alternative Treatments
Rifampin: May be considered for mild cases in pregnant women or those with documented allergy to tetracycline-class drugs. Dosage: 300 mg orally twice daily for adults or 10 mg/kg body weight for children (not to exceed 300 mg/dose) 1
Chloramphenicol: While sometimes used for Rocky Mountain Spotted Fever, it is NOT effective for ehrlichiosis based on in vitro evidence 1
Ineffective Antibiotics
The following antibiotics are NOT effective against ehrlichiosis and should be avoided 1:
- Beta-lactams (penicillins, cephalosporins)
- Macrolides
- Aminoglycosides
- Sulfonamides (may worsen disease)
- Fluoroquinolones (E. chaffeensis exhibits in vitro resistance)
Hospitalization Criteria
Consider hospitalization for patients with 1:
- Evidence of organ dysfunction
- Severe thrombocytopenia
- Mental status changes
- Need for supportive therapy
Special Populations
Pregnant Women
While tetracyclines are generally contraindicated during pregnancy, the benefits of doxycycline may outweigh risks in life-threatening situations 1. Rifampin may be considered as an alternative for pregnant women with mild disease 1.
Immunocompromised Patients
Patients who are immunosuppressed due to HIV, organ transplantation, or immunosuppressive therapies are at higher risk for severe disease and death 1. Prompt recognition and treatment are particularly important in this population.
Prevention
- Preventive antibiotic therapy after tick bites is NOT recommended for asymptomatic individuals 1
- Avoid tick exposure during peak activity periods
- Perform thorough tick checks after outdoor activities
- Remove attached ticks promptly
- Apply DEET-containing insect repellent when in tick-endemic areas
Pitfalls to Avoid
- Delaying treatment: Never wait for laboratory confirmation before starting doxycycline when ehrlichiosis is suspected
- Misinterpreting rash: Rash that develops during treatment may be part of the disease, not a drug reaction
- Using ineffective antibiotics: Particularly sulfa drugs, which may worsen disease
- Withholding doxycycline from children: The risk of dental staining is minimal with short courses and is outweighed by the risk of untreated disease