Onchocerciasis (River blindness)

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Introduction

  • A common chronic filarial disease in tropical regions which frequently cause pruritus and blindness
  • Causative organism is Onchocerca volvulus
  • The microfilariae are transmitted by female Simulium, tiny black flies which breed along small, rapidly moving streams
  • Female worms release motile microfilariae into the skin, subcutaneous issues, lymphatics, and eyes
  • Interval from exposure to onset of symptoms can be as long as 1 - 3 years

Clinical features

  • Skin lesions which may be localized or cover large areas
  • Intense pruritus is a cardinal symptom; may occur in the absence of the skin lesions
  • Dermatitis
  • Skin eventually becomes lichenified from chronic scratching
  • Post inflammatory confetti-like depigmentation on the skin ("leopard skins") may occur in late onchodermatitis
  • Onchocercomata
    • Subcutaneous nodules which develop on various sites of the body and contain myriad adult worms which can live for up to 14 years.
  • Firm, non-tender lymphadenopathy is a common finding in patients with chronically infected onchocerciasis
  • "Hanging groin" describes the pendulous loose, atrophic skin sac that contains these large nodes
  • Microfilariae in the eye may lead to visual impairment and blindness

Differential diagnoses

  • Scabies
  • Pediculosis
  • Papular urticaria
  • Papulonecrotic tuberculids
  • Pruritic papular eruption of HIV
  • Other causes of generalized pruritus without a rash
  • Other causes of subcutaneous nodules e.g.
    • Sparganosis
    • Paragonimiasis
    • Gnathostomiasis
    • Cysticercosis
    • Echinococcosis

Complication

  • Blindness

Investigations

  • Skin snips or punch biopsy for microfilariae
  • Excise nodule for adult worms
  • Mazzotti test reaction
  • Slit lamp eye examination

Treatment goals

  • Kill the microfilariae
  • Eliminate source of microfilarial release
  • Prevent blindness

Drug treatment

Ivermectin

  • As a single oral dose of 150 microgram/kg in adults and children over 5 years
  • Repeat every 6 months for 2 years and yearly for 12 -15 years or longer

Eye involvement

  • Prednisolone 1 mg/kg orally should be started several days before treatment with ivermectin

Surgical

  • Excise individual nodules (nodulectomy)

Notable adverse drug reactions, contraindications, and caution

  • No food or alcohol should be taken for at least 2 hours before or after dosage
  • Pregnant women should not receive ivermectin until after delivery
  • Breastfeeding mothers should not be treated until the infant is at least 1 week old

Prevention

  • Use biodegradable insecticides to kill flies
  • Netting and repellents remain crucial.
  • Provide access to safe and portable water
  • In hyperendemic areas, treat the whole population twice yearly with ivermectin