IAMAT |International Association of Medical Assistance to Travellers| IAMAT |International Association of Medical Assistance to Travellers|

River Blindness

Photo By: Ian Calvert

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.

There is no preventive medication or vaccine against River Blindness.

River Blindness images, life cycle, and distribution maps:

Infection Landscapes

Information last updated: January 2020

Risk of River Blindness is present in the following countries:

Travel Health Journal