Onchocerciasis (River Blindness)

Introduction

Onchocerciasis otherwise called River Blindness is a common chronic filarial disease in tropical regions which frequently causes pruritus and blindness.
Causative organism of this disease condition 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.

Symptoms and clinical features River blindness

Interval from exposure to onset of symptoms can be as long as 1-3 years.
The symptoms of Onchocerciasis include the following:
Skin lesions

  • May be localized or cover large areas.

Intense pruritus

  • 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 of Onchocerciasis (River blindness)

  • Blindness

Investigations

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

Treatment for Onchocerciasis (River blindness)

Treatment objectives

  1. Kill the microfilariae
  2. Eliminate source of microfilarial release
  3. 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, caution and contraindications

  • 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