River Blindness

Guinea: For Specific Travellers

River Blindness


River Blindness, also known as Onchocerciasis, is caused by the Onchocerca volvulus worm which is transmitted from person to person by daytime biting infected blackflies belonging to the genus Simulium damnosum. Infective larval worms (microfilariae) develop in the blackfly and once injected into humans through a blood meal, the worms form nodules, reproduce, and migrate to subcutaneous tissue where they can be ingested by blackflies to continue the infectious cycle. The intensity of the illness is related to the number of bites sustained. River Blindness is a Neglected Tropical Disease (NTD)*.

* Neglected Tropical Diseases are chronic infections that are typically endemic in low income countries. They prevent affected adults and children from going to school, working, or fully participating in community life, contributing to stigma and the cycle of poverty.


Adventure travellers, humanitarian workers, missionaries, and military personnel are at greater risk of being exposed to blackflies. The disease is mostly found in rural villages located near rapidly flowing streams and rivers where blackflies breed.


The illness is typically characterized by skin complications and visual impairment. Many cases are asymptomatic – persons do not exhibit symptoms. T hose with symptoms get ill 9 to 24 months after exposure (worms can live in humans for 10 to 15 years). Symptoms include a skin rash, eye lesions, and bumpy skin. Eye lesions can progress to blindness. Treatment includes taking anthelmintic drugs.


Travellers should take precautions against blackfly bites.

  • Use a repellent containing 20%-30% DEET or 20% Picaridin on exposed skin. Re-apply according to manufacturer's directions.
  • Wear neutral-coloured (beige, light grey) clothing. If possible, wear long-sleeved, breathable garments.
  • If available, pre-soak or spray outer layer clothing and gear with permethrin.
  • Ensure that door and window screens work properly.
  • Apply sunscreen first followed by the repellent (preferably 20 minutes later).
  • For more details, see IAMAT's insect bite prevention.

There is no preventive medication or vaccine against River Blindness.

River Blindness images, life cycle, and distribution maps: Infection Landscapes

Information last updated: February 23, 2021. 

  • Cooper P, Nutman T. Onchocerciasis. In: McGill, A; Ryan, E; Hill, D; Solomon, T, eds. Hunter's Tropical Medicine and Emerging Infectious Diseases. 9th ed. New York: Saunders Elsevier; 2013: 827-834.
  • Hoerauf A. Onchocerciasis. In: Guerrant, R; Walker D; Weller P, eds. Tropical Infectious Diseases. 3rd ed. New York: Saunders Elsevier; 2011: 741-749.
  • Wertheim, Heiman; Horby, Peter; Woodall, John, eds. Atlas of Human Infectious Diseases. Oxford: Wiley-Blackwell; 2012. 273 p.
  • Centers for Disease Control and Prevention: Onchocerciasis (also known as River Blindness)
  • World Health Organization: Onchocerciasis Fact Sheet No. 374