Ehrlichia and Anaplasma

Overview & Pathophysiology - Tiny Intracellular Terrors

• Organisms: Ehrlichia chaffeensis & Anaplasma phagocytophilum are obligate intracellular, gram-negative-like bacteria lacking peptidoglycan and LPS.
• Lifecycle: Transmitted by ticks, they invade host leukocytes, replicating within phagosomes to form characteristic mulberry-shaped aggregates called morulae.
  • They prevent phagolysosome fusion, ensuring their survival.
  • Cell lysis releases bacteria, spreading the infection.
• Cell Tropism: 📌 MEGA - Ehrlichia infects Monocytes; Anaplasma infects Granulocytes.

⭐ The presence of intracytoplasmic morulae in neutrophils (Anaplasma) or monocytes (Ehrlichia) on a peripheral blood smear is a key diagnostic clue.

Ehrlichia vs. Anaplasma - The Great Divide

⭐ High-Yield: Anaplasma shares its Ixodes tick vector with Borrelia (Lyme disease) and Babesia, so be suspicious of co-infections.

Clinical & Lab Findings - Fever, Chills, Low Counts

• Acute Presentation: Abrupt onset of high fever, chills, headache, and myalgias.
  • Rash is uncommon, but more frequent in Ehrlichiosis (~30%) vs. Anaplasmosis (<10%).
• Key Lab Abnormalities:
  • ↓ Leukopenia (WBC < 4,500/mm³)
  • ↓ Thrombocytopenia (Platelets < 150,000/mm³)
  • ↑ Elevated serum aminotransferases (ALT/AST)

⭐ High-Yield: Diagnosis is often confirmed by finding morulae (Latin for 'mulberry')-intracytoplasmic inclusions of organisms-within granulocytes (Anaplasma) or monocytes (Ehrlichia) on a peripheral blood smear.

Diagnosis & Management - Spot the Dot, Treat Right

• Labs: Pancytopenia (↓ platelets, ↓ WBCs), ↑ liver enzymes.
• Microscopy: Key finding is morulae (intracytoplasmic, mulberry-like inclusions).
  • Ehrlichia chaffeensis: Monocytes
  • Anaplasma phagocytophilum: Granulocytes
• Gold Standard: PCR for definitive diagnosis.
• Treatment: Empiric Doxycycline is first-line for all patients, including children. Do not delay therapy awaiting confirmation.

⭐ Intracytoplasmic morulae are highly specific but insensitive, seen in <10% of patients.

High‑Yield Points - ⚡ Biggest Takeaways

• Obligate intracellular bacteria transmitted by ticks (Ehrlichia: Lone Star tick; Anaplasma: Ixodes tick).
• Ehrlichia infects monocytes (HME), while Anaplasma infects granulocytes (HGA).
• Clinical presentation includes fever, headache, and malaise.
• Key lab findings: pancytopenia (leukopenia, thrombocytopenia) and elevated liver enzymes.
• Diagnosis is confirmed by seeing morulae (mulberry-like inclusions) in the cytoplasm of infected cells.
• Treatment for both is Doxycycline.