Ehrlichiosis

Human monocytic ehrlichiosis (HME) is a tick borne infection by Ehrlichia chaffeensis (lone star tick, Amblyomma americanum), with E. ewingii and E. muris eauclairensis causing similar disease.

• Mostly south central and southeastern United States; also reported in Africa, Asia, and Latin America.
• Incubation is 5 to 14 days. Seasonal peak in spring and summer.
• Case fatality about 1 to 3% (higher in immunocompromised and elderly).
• Severe disease: toxic-shock-like presentation, multiorgan failure, and HLH.

• Fever, headache, myalgia, malaise, nausea, vomiting, and diarrhoea.
• Rash in about 30% (more in children), leukopenia, thrombocytopenia, and transaminitis.
• Neurological involvement: confusion, meningoencephalitis.
• Complications: respiratory distress, DIC, renal failure, hepatitis, and secondary opportunistic infections.

• PCR on blood (sensitive in the first week), morulae in monocytes (under 10% of cases), and paired IFA serology.
• Blood count (leukopenia, lymphopenia, thrombocytopenia), liver tests, LDH, ferritin (HLH screening), CSF if neurological.
• Exclude anaplasmosis, RMSF, tularaemia, viral illness, infectious mononucleosis, and leptospirosis.
• Treat empirically on suspicion.

• Doxycycline 100 mg orally or IV every 12 hours (2.2 mg/kg twice daily for children under 45 kg) for at least 5 to 7 days, continued for at least 3 days after fever resolves.
• Severe disease: IV doxycycline, ICU support, and management of HLH with dexamethasone, IVIG, or etoposide as needed.
• Rifampicin 300 mg twice daily for 7 to 10 days only in pregnancy with doxycycline allergy (limited evidence).
• Chloramphenicol is not effective.
• Tick bite prevention and prompt tick removal.
• Follow up for response within 48 hours; persistent fever suggests alternative diagnosis or co-infection.