Filariasis

Filariasis Basics - Wormy Intruders

• Lymphatic Filariasis (LF): Chronic parasitic disease; affects lymphatics.
• Causative Agents: Nematodes (filarial worms).
  • Wuchereria bancrofti (~90% cases).
  • Brugia malayi.
  • Brugia timori.
• Vectors: Mosquitoes.
  • Culex quinquefasciatus (urban W. bancrofti).
  • Anopheles spp. (rural W. bancrofti).
  • Mansonia spp. (Brugia).
• Transmission: Infective L3 larvae from mosquito bite. Microfilariae (mf) in blood.
• Endemic in India.

⭐ Wuchereria bancrofti exhibits nocturnal periodicity (mf peak in peripheral blood at night, 10 PM - 2 AM).

Vectors & Lifecycle - Mosquito Mailmen

• Vectors (Mosquitoes):
  • W. bancrofti: Culex (urban), Anopheles (rural), Aedes.
  • B. malayi: Mansonia, Anopheles.
  • B. timori: Anopheles barbirostris.
• Lifecycle:
  • Mosquito (intermediate host) deposits L3 larvae on skin.
  • L3 larvae enter skin, migrate to lymphatics.
  • Mature into adult worms (human: definitive host).
  • Adults release microfilariae (L1) into blood.
  • Mosquito ingests L1; develop to L3 in mosquito.

⭐ W. bancrofti microfilariae show nocturnal periodicity (peak 10 PM - 2 AM). (📌 Mnemonic: "Bankers work late")

Clinical Picture - Elephant Tales & More

• Asymptomatic Microfilaremia: Common; asymptomatic despite blood microfilariae.
• Acute Lymphatic Filariasis:
  • Adenolymphangitis (ADL) / Filarial Fever: Recurrent fever, chills, painful lymphadenopathy & retrograde lymphangitis.
  • Acute epididymo-orchitis, funiculitis (esp. males).
• Chronic Lymphatic Disease (Develops over years):
  • Lymphedema: Progressive: pitting → brawny, non-pitting edema.
  • Hydrocele: Most common in Bancroftian filariasis; scrotal swelling.
  • Elephantiasis: Irreversible enlargement (limbs, scrotum, penis, vulva, breasts). Skin hyperkeratotic, coarse, fissured.
  • Chyluria: Milky urine (lymphatic fluid, chyle).
• Occult Filariasis (e.g., Tropical Pulmonary Eosinophilia - TPE):
  • Blood microfilariae absent (sequestered in lungs/tissues).
  • Nocturnal cough, wheeze, dyspnea, marked eosinophilia, ↑IgE.

  ⭐ Hydrocele is the most common chronic manifestation of Bancroftian filariasis.

Diagnosis Decoded - Finding Filaments

• Microfilariae (MF) Detection: Key for diagnosis.
  • Peripheral Blood Smear (PBS): Gold standard.
    • Timing: Nocturnal sample (10 PM - 2 AM) for W. bancrofti, B. malayi.
    • Stain: Giemsa. Thick/thin smears examined.
  • Concentration Methods: ↑ sensitivity (e.g., Knott's, membrane filtration).
  • QBC (Quantitative Buffy Coat): For MF detection using fluorescence microscopy.
  • DEC Provocation Test: Induces daytime appearance of MF after 2 mg/kg DEC dose.
• Adult Worm Detection:
  • Ultrasound (USG): "Filarial dance sign" (visualization of live, motile adult worms in lymphatics).
  • Biopsy: Lymph node or nodule biopsy may show adult worms.
• Antigen Detection (W. bancrofti):
  • Immunochromatographic Card Test (ICT): Detects Circulating Filarial Antigen (CFA).

  ⭐ CFA tests (e.g., ICT) can be positive even in amicrofilaremic (occult) filariasis and chronic infections.

Management & Defense - Worm Warfare

• Drug of Choice (DOC): Diethylcarbamazine (DEC).
  • Regimen: 6 mg/kg/day orally for 12 days.
  • Action: Potent microfilaricidal; also damages adult worms.
  • ⚠️ Caution: Mazzotti reaction (systemic/local inflammation from dying mf); manage with antihistamines/corticosteroids.
• Lymphedema Care: Meticulous hygiene, limb elevation, exercises, compression; Complex Decongestive Therapy (CDT).
• Hydrocele: Surgical management (hydrocelectomy).
• Mass Drug Administration (MDA): Annual single dose of DEC (6 mg/kg) with Albendazole; or Ivermectin + Albendazole.
• Vector Control: Integrated strategies against mosquito vectors (IRS, larviciding, LLINs).

⭐ DEC is the only drug effective against adult filarial worms (macrofilaricidal), particularly W. bancrofti.

High‑Yield Points - ⚡ Biggest Takeaways

• Causative agents: Wuchereria bancrofti, Brugia spp.; Vector: Mosquitoes.
• Hallmark: Chronic lymphedema leading to elephantiasis and hydrocele.
• Acute episodes: Recurrent adenolymphangitis (ADL) with fever and painful lymphadenopathy.
• Diagnosis: Nocturnal blood smear for microfilariae; ICT card test for W. bancrofti antigen.
• Treatment: Diethylcarbamazine (DEC) is mainstay; doxycycline for Wolbachia.
• Tropical Pulmonary Eosinophilia (TPE): Occult filariasis with nocturnal cough, marked eosinophilia.
• Control: Mass Drug Administration (MDA); vector control.