ONCHOCERCIASIS (river blindness)

Chronic filarial disease present in areas around rivers

Cause

  • Onchocerca volvulus, transmitted by a bite from a female black fly (Simulium damnosum, S. naevi and S. oodi, etc), which breeds in rapidly flowing and well-aerated water

Clinical features

Skin

  • Onchocercoma: painless smooth subcutaneous nodules containing adult worms, adherent to underlying tissues, usually on body prominences like iliac crests, pelvic girdle, ribs, skull
  • Acute papular onchodermatitis: Intense pruritic rash, oedema (due to microfilariae)
  • Late chronic skin lesions: dry thickened peeling skin (lizard skin), atrophy, patchy depigmentation

Eye

  • Inflammation of the eye (of the cornea, uvea, retina) leading to visual disturbances and blindness

Differential diagnosis

  • Other causes of skin depigmentation (e.g. yaws, burns, vitiligo)
  • Other causes of fibrous nodules in the skin (e.g. neurofibromatosis)

Investigations

  • Skin snip after sunshine to show microfilariae in fresh preparations
  • High eosinophils at the blood slide/CBC
  • Excision of nodules for adult worms
  • Slit-lamp eye examination for microfilariae in the anterior chamber of eye

Management

Case treatment (adult worms)

  • Doxycycline 100 mg twice a day for 6 weeks followed by
  • Ivermectin 150 micrograms/kg single dose

Mass treatment

  • Ivermectin 150 micrograms/kg once yearly for 10-14 years (see also dose table below)
    • Not recommended in children <5 years, pregnancy, or breast-feeding mothers
    • No food or alcohol should be taken within 2 hours of a dose

Ivermectin dose based on height

HEIGHT (CM) DOSE
>158 12 mg
141–158 9 mg
120–140 6 mg
90–119 3 mg
< 90 Do not use

Prevention

  • Vector control
  • Mass chemoprophylaxis