Makindo Medical Notes

🕷️ The symptoms of Ehrlichiosis usually develop 1–2 weeks after being bitten by an infected tick. The bite is painless, and about 50% of patients do not recall being bitten. Delay in treatment ⏳ increases the risk of severe complications or death.

📖 About

• Ehrlichiosis is a serious tick-borne zoonosis caused by obligate intracellular Gram-negative bacteria of the genus Ehrlichia.
• It infects white blood cells (monocytes or granulocytes), disrupting host immunity.
• Immunocompromised patients have a significantly higher case-fatality rate ⚠️.
• Can be rapidly fatal if untreated—even in previously healthy individuals.

🔬 Characteristics

• Obligate intracellular bacteria, similar to Rickettsia, but they lack peptidoglycan and lipopolysaccharides.
• Form clusters inside leukocytes called morulae, visible on microscopy.
• Spread through tick bites; no human-to-human transmission.

🌍 Source

• Transmitted by ticks—most commonly the Lone Star tick (Amblyomma americanum) in the USA and Ixodes scapularis (black-legged tick).
• Reservoirs include deer, dogs, and rodents.
• Human cases peak in late spring and summer, coinciding with tick activity.

🦠 Pathogenicity

• Bacteria invade monocytes, macrophages, or neutrophils, depending on species.
• Block phagolysosome fusion → survival inside cells.
• Trigger inflammatory cytokine release → fever, sepsis-like syndrome.
• Main human pathogens:
  • E. chaffeensis → human monocytic ehrlichiosis (HME).
  • E. ewingii → ehrlichiosis in immunocompromised patients.
  • E. muris-like agent (Midwest USA).

🩺 Clinical Symptoms

• Early (days 1–7): Fever 🌡️, chills, severe headache, myalgia, malaise.
• GI symptoms: Nausea, vomiting, diarrhoea, abdominal pain.
• Neurological: Confusion, seizures, or altered mental status in severe cases.
• Ocular: Conjunctival injection (red eyes).
• Rash: Occurs in ~30% overall, more common in children 👶.
• Complications: Acute respiratory distress syndrome (ARDS), meningoencephalitis, multi-organ failure.

🔎 Investigations

• FBC: Leucopenia, thrombocytopenia, and raised liver enzymes (AST/ALT).
• PCR: Detects Ehrlichia DNA early (but a negative does not rule it out).
• Serology: IgG antibody titres appear after 7–10 days (paired acute + convalescent samples confirm diagnosis).
• Blood smear: May show morulae in monocytes/neutrophils (seen in ~20% of patients).

💊 Management

• Immediate empiric treatment: Do not delay for lab confirmation.
• Doxycycline is first-line for all ages:
  • Adults: 100 mg PO/IV every 12 hrs.
  • Children: 2.2 mg/kg (max 100 mg) twice daily.
• Duration: 7–10 days, minimum 3 days after defervescence.
• Supportive care: IV fluids, oxygen, ICU support if ARDS/sepsis develops.
• Chloramphenicol is NOT effective (unlike rickettsial infections).

📌 Key Exam Pearls

• Think of ehrlichiosis in a patient with tick exposure + fever + cytopenias + ↑LFTs.
• No rash in most adults → distinguishes it from RMSF (Rocky Mountain spotted fever).
• Start doxycycline empirically in suspected cases—delayed therapy ↑ mortality.
• Morulae on blood film = diagnostic clue 🧫.