Ehrlichiosis
🕷️ 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 🧫.
