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Internal Medicine

Onchocerciasis

Onchocerciasis, also known as the African river blindness is an eye and skin disease caused by a worm known as Onchocerca volvulus.

Onchocerciasis, also known as the African river blindness is an eye and skin disease caused by a worm known as Onchocerca volvulus.

  • #2 M/C cause of infectious blindness worldwide after trachoma

Parasitology

Onchocerca volvulus:

  • Definitive hosts: Humans
  • Larval stages grow exclusively in the Simulium black fly
Life cycle of Onchocerca volvulus | Hopkins A. (2017). Onchocerciasis then and now: achievements, priorities and challenges. Community eye health, 30(100), 92–95.

Epidemiology

The baseline endemicity of onchocerciasis in APOC countries. | Hopkins A. (2017). Onchocerciasis then and now: achievements, priorities and challenges. Community eye health, 30(100), 92–95.
Phases of elimination | Hopkins A. (2017). Onchocerciasis then and now: achievements, priorities and challenges. Community eye health, 30(100), 92–95.

Clinical features

The disease manifests either as ocular or as dermal onchocerciasis with several symptoms including itching, nodules, skin thickening, visual impairment and blindness.

Ocular oncocerciasis:

  • Anterior segment:
    • Live microfilariae in anterior chamber (AC)
    • Punctate keratitis, leading on to sclerosing keratitis
    • Early uveitis, leading on to chronic uveitis
  • Posterior segment:
    • Choroido-retinitis, leading on to choroido-retinal atrophy or optic nerve atrophy
    • Acute optic neuritis, leading on to optic atrophy
  • Others:
    • Night blindness
    • Visual field loss and constriction
    • Irreversible blindness
Sclerosing keratitis in onchocerciasis | Photos: Ian Murdoch & Allen Foster

Dermal oncocerciasis:

Non-ocular manifestations
  • Severe pruritus
  • Subcutaneous painless nodules (typically found around bony prominences)
  • Severe, disfiguring skin disease
  • Lymphadenopathy, hanging groin
  • Unproven but suspected associations: hyposexual dwarfism, higher prevalence of epilepsy

Management

Vector control:

Chief strategy aiming to interrupt transmission of O. volvulus by regular aerial spraying of all Simulium larval breeding sites, and to maintain this for at least 14 years until the infection has died out in human populations.

Ivermectin:

Only chemotherapeutic agent recommended for use against onchocerciasis

Community-wide treatment:

Method of choice in meso- and hyperendemic areas of onchocerciasis where ivermectin is given once a year for at least 14 years to all members of the community

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