Wuchereria & Brugia

• Wuchereria bancrofti

  Bancroft's filarial worm
• Brugia malayi


  Malayan filarial worm
• Brugia timori has similar effects with Brugia malayi
• Most are secondary to Wuchereria bancrofti
• Lymphatic filariasis


  • One of the most debilitating diseases in tropical countries
  • Second leading cause of permanent and long-term disability, affecting both physical and psychological aspects (next to psychiatric illness)
• Lymphatic filariasis

  • Causes long-term disabilities such as elephantiasis and hydrocoele
  • Depression and psychotic disorders could develop secondary to long-term disabilities caused by lymphatic filariasis
• Infective stage

  Third stage larva
• All filarial nematodes have L3 as the infective stage to humans

  
• Diagnostic stage

  • Microfilariae
  • Adult worm

  
• Adult nematode is a diagnostic stage when it is manually extracted
• Wuchereria bancrofti

  Causing Bancroftian filariasis
• Brugia malayi

  Causing Malayan filariasis
• Lymphatic filariasis is a cosmopolitan parasitic infection

  
• 120M people affected worldwide, 83 endemic countries
• Wuchereria bancrofti affects 90% of cases
• Brugia spp. affects 10%
• Davao region is endemic to filariasis
• Adult worms

  • Creamy white, long, filiform in shape
  • Found tightly coiled in nodular dilated nests (lymphangiectasis) in lymph vessels and sinuses of lymph glands

  
• Lymphangiectasis


  A pathologic dilation of lymph vessels
• Adult worms

  • Male: 20 - 40 mm
  • Female: 80 - 100 mm

  
• Microfilaria


  Pre-larval form of the filarial worm

  
• Microfilaria

  • Minute, snake-like organisms constantly moving among RBC
  • Several curvatures and graceful appearance
  • Measurement: 270 - 290 um
  • Enclosed in hyaline sheath that is longer than the microfilaria
• Hyaline sheath

  Lighter staining structures external to the microfilaria
• There are other species of filarial worms that do not have the sheath (unsheathed)
• Dark-staining nuclei are important to species identification
• Characteristics

  • Wuchereria
  • Brugia
• Wuchereria

  • Appearance: Smoothly curved
  • Terminal Nuclei: Absent
  • Prevalance: Widespread
  • Mosquito vector: Culex, Aedes, Anopheles
  • Preference: Scrotal lymphatics
  • Clinical picture: Hydrocele
  • Severity: More severe
  • Cephalic space length to width ratio: 1:1
  • Stylet at anterior end: Single
  • Excretory pore: Not prominent
  • Nuclei column: Large course discrete nuclei
  • Tail: Pointed and free of nuclei
  • Sheath: Faintly stained
• Brugia

  • Appearance: Kinky with secondary curves
  • Terminal Nuclei: Present
  • Prevalance: Southeast Asia only
  • Mosquito vector: Mansonia
  • Preference: Limb lymphatics
  • Clinical picture: Elephantiasis
  • Severity: Less severe
  • Cephalic space length to width ratio: 2:1
  • Stylet at anterior end: Double
  • Excretory pore: Prominent
  • Nuclei column: Overlapping blurred nuclei
  • Tail: Pointed with 2 distinct nuclei
  • Sheath: Well stained
• Life Cycle of W. bancrofti (and B. malayi/timori; dif. Vector)

  1. Infected mosquito carries L3 larva (infective stage in humans)

  2. L3 goes to the human lymphatics, establishes itself and matures into male and female adults

  3. Adults stay in lymph nodes, copulate, and female adult gives birth to microfilariae

  4. Microfilariae go to blood circulation

  5. Mosquito bites infected person and becomes infected with microfilariae

  6. Inside mosquito, microfilaria unsheathes and migrates to muscle, molts to L1, L2, L3

  7. L3 larva migrates to head and proboscis of mosquito

  8. When mosquito bites human, human becomes infected with L3 larva

  
• The life cycle of the causative agents of lymphatic filariasis are similar, the difference lies on the vectors of these parasites

  
• Pathogenesis

  • Infection usually acquired during childhood
  • Takes years to manifest
  • Requires a lot of worms to cause structural deformity

  
• Adult worms in lymph nodes

  Cause inflammation that obstructs lymphatic vessels, leading to Lymphedema

  
• Obstruction is caused by adult male and female worms
• Lymphedema


  "Hupong," generally unilateral, but can be bilateral
• Microfilariae DO NOT cause symptoms
• Clinical course

  • Asymptomatic
  • Acute stage
  • Chronic
• Clinical spectrum of Lymphatic Filariasis


  • Asymptomatic microfilaremia
  • Acute Dermatolymphangioadenitis
  • Acute Filarial Lymphangitis
  • Lymphedema and Elephantiasis
  • Genitourinary Lesion such as hydrocoele
  • Tropical Pulmonary Eosinophilia
• Asymptomatic microfilaremia

  Blood thick smear identifies asymptomatic microfilaremia, common in endemic areas
• Acute Dermatolymphangioadenitis (ADLA)


  Inflammation of the lymph nodes in the skin, caused by Group A Streptococcus, not caused by the parasite
• Acute Filarial Lymphangitis (AFL)


  Directly caused by adult worms that died spontaneously or following treatment, self-limited