Treatment of Anaplasmosis Caused by Anaplasma phagocytophilum
Doxycycline is the treatment of choice for anaplasmosis caused by Anaplasma phagocytophilum, with a dosage of 100 mg twice daily for 10 days in adults. 1
First-line Treatment
Doxycycline
- Adults: 100 mg orally twice daily for 10 days
- Children: 4 mg/kg per day in 2 divided doses (maximum 100 mg per dose) for 10 days
- For patients unable to take oral medications, intravenous doxycycline can be administered at the same dosage
Doxycycline is highly effective against A. phagocytophilum and typically leads to clinical improvement within 24-48 hours of initiation 1. This rapid response to doxycycline is so characteristic that failure to improve within this timeframe should prompt reconsideration of the diagnosis or evaluation for potential coinfections 1.
Alternative Treatment Options
Rifampin
Rifampin may be used as an alternative in specific situations:
- Patients with documented severe allergy to tetracyclines
- Pregnant women
- Children under 8 years of age
Dosage:
- Adults: 300 mg orally twice daily for 7-10 days
- Children: 10 mg/kg twice daily (maximum 300 mg per dose) for 7-10 days 1
Important Cautions with Rifampin
- Patients treated with rifampin should be closely monitored to ensure resolution of clinical and laboratory abnormalities 1
- Before using rifampin, clinicians must rule out Rocky Mountain Spotted Fever (RMSF), as rifampin is not effective against RMSF and the early symptoms of RMSF and anaplasmosis can be similar 1
- Rifampin does not effectively treat potential coinfection with Borrelia burgdorferi (Lyme disease) 1
Ineffective Treatments to Avoid
Several antimicrobials should NOT be used for anaplasmosis treatment:
Chloramphenicol: In vitro evidence indicates it is not effective against anaplasmosis 1
Fluoroquinolones: Despite in vitro susceptibility of A. phagocytophilum to levofloxacin, clinical relapse after treatment has been documented. A case report showed a patient who initially improved with levofloxacin but relapsed 15 days after completing therapy 2. This treatment failure was also reproduced in an animal model 2.
Beta-lactams, macrolides, aminoglycosides, and sulfonamides: These broad-spectrum antibiotics are ineffective against A. phagocytophilum 1
Sulfonamides (including trimethoprim-sulfamethoxazole): Associated with increased disease severity in tickborne rickettsial diseases 1
Special Considerations
Coinfections
The tick vector for A. phagocytophilum (Ixodes scapularis) can also transmit other pathogens including Borrelia burgdorferi (Lyme disease) and Babesia microti. Coinfection with B. burgdorferi has been reported in up to 10% of patients with Lyme disease 1.
If coinfection with B. burgdorferi is suspected or confirmed in patients receiving rifampin for anaplasmosis, additional treatment with amoxicillin or cefuroxime axetil is necessary, as rifampin is not effective against B. burgdorferi 1.
Severe Disease
In severe cases of anaplasmosis that progress to hemophagocytic lymphohistiocytosis (HLH), a combination of doxycycline, steroids, and anakinra (an IL-1 receptor antagonist) has been successfully used 3. This highlights that severe immune-mediated complications may require both antimicrobial and immunosuppressive therapy.
Monitoring Response
Patients should show clinical improvement within 24-48 hours after starting doxycycline 4. Laboratory abnormalities typically include:
- Leukopenia
- Thrombocytopenia
- Elevated hepatic transaminases
- Mild anemia
These parameters should be monitored to assess treatment response, particularly in hospitalized patients.
Conclusion
Early recognition and prompt initiation of appropriate antibiotic therapy are critical in preventing complications of anaplasmosis. While most patients recover uneventfully even without specific treatment, delayed diagnosis in older or immunocompromised patients may lead to severe disease and potentially death 4.