Oncho

• Onchocerca volvulus

  AKA blinding worm

  
• Vector

  • Female Simulium Blackflies
• Infective Stage

  Third Stage Larva (L3)
• Infective stage of all filarial spp.

  
• Diagnostic Stage

  • Microfilaria in skin, lymphatics, occasional in blood, urine, sputum
  • Adults in lymph nodes
• Habitat

  Subcutaneous tissues,
• Found in Africa, and Central and South America
• In areas with fast-flowing rivers
• River Blindness


  Debilitating disease caused by Onchocerca
• NOT endemic in our country
• Adult Male

  • 19 – 42 mm by 130 – 210 um
• Adult Female

  • 33 – 50 cm by 270 – 400 um
  • Produce microfilariae in the subcutaneous nodules for 9 years
• Microfilaria


  • Location: nodules under the skin
  • Occasionally, in the blood, urine, sputum
  • Measurement: 220 – 360 um by 5 – 9 um
  • Life span: 2 years
  • Unsheathed
  • No nuclei at the tip of the tail
• Life cycle of O. volvulus

  1. Vector bites the human host, introducing the L3

  2. In the subcutaneous tissue, they become male and female adults and copulate

  3. Female gives birth to microfilariae (infective stage to the blackfly)

  4. In the body of the blackfly, the microfiariae matures to L1, molts to develop into L2 and eventually L3

  5. L3 migrates to the head and proboscis of the blackfly and when the fly bites humans, the human is infected with L3 and the cycle continues

  
• Wolbachia causes symptoms of Onchocerciasis
• Symptoms of Onchocerciasis

  • Caused not by the parasite, but by the Wolbachia (bacteria)
  • When parasites die, bacteria are released causing an immune response which causes colalteral tissue damage as it tries to contain the infection

  
• Onchocerciasis

  • River blindness: most serious manifestation
  • Onchocercoma: Subcutaneous nodules
  • Lizard Skin: Atrophy and dryness of the skin, itchy
  • Hanging Groin: Affects the lymph nodes, the groin would appear hanging

  
• Diagnosis

  1. Skin Snips: Microfilaria (Anytime)

  2. Biopsy of Skin Nodules: Adult worm with Wolbachia and microfilariae
• Treatment


  1. Ivermectin plus Doxycycline: Ivermectin – Kills larvae, Doxycycline – Kills Wolbachia, thus, killing adults

  2. Mazzotti Reaction: Hypersensitivity reaction due to lysis of worms

  3. Old drugs but no more recommended: Diethylcarbamazine (DEC): Kills microfilariae → Accelerates blindess, Suramin: Kills adult worm, highly toxic

  
• Prevention and Control

  • Insect repellant
  • Wearing clothes covering skin