Ocular onchocerciasis

Definition

Onchocerciasis is a disease of the eyes and skin caused by a worm whose scientific name is Onchocerca volvulus.

Organ

Onchocerciasis causes damage to the cornea.

Symptoms

Dermatologically, it causes itching, rashes and subcutaneous nodules.

In the eye, it causes itching, redness, lesions affecting the cornea and retina, and damage to the optic nerve leading to reduced vision.

Frequency

Onchocerciasis is the second most common infectious cause of blindness worldwide.

Onchocerciasis is a major cause of blindness in many African countries. It is a public health problem in West and Central Africa, but is also present in Yemen and six Latin American countries. In the past, onchocerciasis has considerably reduced economic productivity in infected areas, and vast tracts of arable land have been abandoned. It is estimated that half a million people are blind as a result of river blindness.

Source: WHO

The majority of infections occur in sub-Saharan Africa, but there are a few cases in the Middle East (notably Yemen), Central America and South America.

Source: New Canadian Children

Causes

Onchocerciasis is an eye and skin disease caused by a worm (filaria) whose scientific name is Onchocerca volvulus. It is transmitted to humans by the bite of a small insect.  These flies reproduce in turbulent waterways, increasing the risk of blindness in people living nearby, hence the common name "river blindness". In the human body, the adult female worm produces thousands of larvae (microfilariae) which migrate into the skin and eyes.

Source: WHO

People living in rural areas near the turbulent rivers of an endemic region (particularly in sub-Saharan Africa) are the most vulnerable to infection.

Source: New Canadian Children

Evolution

If left untreated, reversible damage to the cornea can lead to permanent corneal opacity and blindness. Inflammation of the optic nerve can also lead to vision loss and blindness.

Long-term skin damage can lead to diffuse rashes, hyperpigmentation (which may be associated with oedema), skin atrophy (thinning and loss of elasticity of the skin) and depigmentation (which can give a 'leopard-skin' appearance, particularly on the lower legs). The terrible, persistent itching can contribute to chronic insomnia or depression.

Source: New Canadian Children

Prevention

River blindness is one of VISION 2020's priority diseases. But the fight against onchocerciasis was initiated long before that. In 1974, the West African Onchocerciasis Control Programme (OCP) began fighting the vector in West Africa. Then in 1996, community-directed mass ivermectin treatment programmes were set up by the African Programme for Onchocerciasis Control (APOC) in other African countries and by the Programme for the Elimination of Onchocerciasis in the Americas (OEPA) in endemic Latin American countries. In 1992 a group of non-governmental development organisations (NGDOs), now called the NGDO Coordination Group for Onchocerciasis Control, was formed to help foster worldwide interest and support for ivermectin treatment in endemic countries in order to eliminate onchocerciasis as a public health problem. It currently consists of 9 international and 1 national NGDO partners. The group's activities are coordinated through its secretariat at WHO headquarters in Geneva. The fight against onchocerciasis is not only a historic success story, but is also proof of the importance of the synergy brought about by the partnership established by the associations in this success story. This fight also has a definite impact on the socio-economic development of the countries involved in these programmes.

Source: WHO

Diagnosis

A dermatological biopsy is taken.

For the eye, an examination of the anterior chamber using a slit lamp is necessary.

Treatment

Environmental control of onchocerciasis consists of killing the larvae using insecticides, in particular by dispersing insecticides in rivers and streams.

Onchocerciasis is treated with ivermectin, which kills the microfiliariae, soothes the itching and halts the progression to blindness. It also reduces transmission by preventing the filarial worms from reproducing.

A single annual dose is all that is needed for the treatment to be effective.