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Onchocerciasis – Symptoms, Causes, Treatment, Diagnosis, Prevention

Written by Dr.Mary

What is Onchocerciasis?

This is also referred to as river blindness and infects over 37 million individuals who are living near fast-moving streams as well as rivers of sub-Saharan area of Africa. A very small number of cases also have been reported out of Yemen and the Americas. Onchocerciasis is believed to be the 4th leading cause of preventable blindness. Approximately 500,000 of individuals infected with onchocerciasis are visually seriously impaired and another approximately 270,000 have become blind permanently from this disease.


99% of all river blindness cases around are found in Africa. In the 1970s, this disease was so prevalent in some river communities that over half of all the adults were blind and many had fled the fertile river valleys. The impact socio-economic of this migration was so bad that it caused the creation of the successful Onchocerciasis Control Program in 1975 that helped to bring down the rates of this disease and caused an economic stability to return to these river communities. In 1995, the African Program for Onchocerciasis Control or APOC was formed with the aim of totally eliminating the disease as a public health concern.

Onchocerciasis Symptoms

This is a disease which is known as a parasitic disease caused by a filarial worm known as Onchocerca volvulus, and is transmitted thru infected blackflies bites. It is normally blackflies of the Simulium species that are infected and transport undeveloped forms of larva of the parasite from one human to another. While in the body, the larvae develop nodules in the tissue of the subcutaneous where these larvae mature to adults. After mating, the female adult worm actually can release up to 1000 microfilariae each day. These transport thru the human body, and upon dying they create an assortment of conditions:

  • Lesions
  • Rashes
  • Depigmentation of the skin
  • Intense itching
  • Lymphadenitis resulting in hanging groins and elephantiasis of genitals
  • General debilitation
  • Serious visual impairment
  • Blindness
  • Swollen lymph nodes
  • Skin elasticity destruction
  • Thick, rough, wrinkled skin

Manifestations of these conditions begin to happen in individuals 1 to 3 years after the injection of larvae that are infective.

The effects on an individual’s vision can be in some cases only mild impairment. For instance blurry vision or total blindness. Early symptoms of river blindness consist of:

Onchocerciasis Diagnosis

This condition can be diagnosed by:

  • Palpation of skin nodes
  • Skin snip examination where small pieces of skin or cultured in growth medium
  • Mazotti test where oral DEC is given and if individual is infected intense pruritus result within 2 hours
  • DEC patch test where a local application of 10% DEC anhydrous lanolin is applied to the skin. The patch is then checked for local dermatitis
  • ELISA where a drop of blood from a pricked finger is collected on filter paper in this serological test. An enzyme-linked immunosorbent assay (ELISA) can then detect the presence of the O. volvulus antigens.
  • PCR – known as Polymerase Chain Reaction

Onchocerciasis Causes

This condition is also known as River blindness and is an infectious disease that is chronic and caused by the Onchocerca volvulus parasitic warm. It is spread to humans by the female blackfly bite – a fly that breeds near swift flowing rivers. The infectious larva is passed by the bite.

The larvae will form nodules under the skin as it develops into an adult which can take a year or more. When any female worm in the nodule is mated, she will produce the eggs that develop into microfilariae.

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It is these microfilariae that migrate out into the skin and eye tissues and it is these microfilariae that are responsible for the infection symptoms.

Onchocerciasis Treatment

Since most of the cause of this condition is ancillary to microfilariae, the aim of any treatment is to eradicate the microfilarial stage of the disease. This improves symptoms, prevents development of eye lesions and interrupts the transmission of disease.

  • Ivermectin is the “drug of choice” with this disease:
  • Repeated doses every three to twelve months for no less than ten to twelve years
  • More numerous dosing for patients who have numerous symptomatic recurrences

Ivermectin is normally well tolerated. The dying microfilaria can cause pruritus. Ocular inflammation can also be triggered by the dying microfilariae. To minimalize this some medical professionals recommend a small course of prednisone for two to three day along with the ivermectin. Also more frequent dosages of ivermectin – every three months instead of every 12 months – may reduce any inflammation complications.

Other drugs for the interruption of the stages of the parasite are currently under research.

Onchocerciasis Prevention

Repellents that contain diethyltoluamide or DEET can provide protection from the bites of the black fly. Heavy clothes, head nets and long sleeves could be necessary for outdoor activity in areas with heavy infestation during peak activity. The control of black flies includes applications of insecticides for both larvae and adults. This has only had limited success since it is difficult to locate and treat all the breeding areas.

Thanks to the African countries participating in the Onchocerciasis Control Program with community-wide administration of ivermection in these areas has greatly reduced the prevalence of blindness in those communities where this disease is endemic.

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