Onchocerciasis also known as River Blindness is a parasitic disease caused by the filarial worm known scientifically as Onchocerca volvulus.

Wondering how it got the name, River Blindness?

The disease is called River Blindness because the black flies that transmit the infection lives and breeds near fast flowing streams or rivers and the infection can result to blindness.

BURDEN OF ONCHOCERCIASIS

The disease is commonly found in regions with tropical climates particularly in the Sub- Sahara with Africa having more of the disease burden.Onchocerciasis is also found in six countries in Latin America and Yemen in the Arabian Peninsula where the disease is believed to have been exported by the slave trade.

The world Health Organization (WHO) estimate shows that at least 25 million people are infected with Onchocerca volvulus Worldwide; of which 300,000 are blind and 800,000 have some sort of visual deterioration, and more than 100 million people run a risk of becoming infected with the parasites.

MODE OF TRANSMISSION

Onchocerciasis is transmitted by a blackfly of the genus simulium spp.  The parasite is transmitted through bites during the day and this is because the blackfly needs blood for the purpose of ovulation. Anyone can become infected with onchocerciasis when the blackfly deposit Onchocerca infective larvae into the blood during a blood suck.

Although,several bites are needed before the person can be infected.  So people who travel for short period of time (generally less than 3 month) to areas where the parasite are found have a low chance of becoming infected with Onchocerca volvulus.

PEOPLE AT RISK

The people at risk for acquiring Onchocerciasis are those who live near streams or rivers where there are simulium black flies. The disease usually occurs after repeated exposures to black flies bite, so short term travelers to region that are endemic are at lower risk.

SYMPTOMS

Severe itching.

Nodules in the skin (subcutaneous nodules or bumps).

Patchy skin depigmentation (leopard skin).

Lump node inflammation (lymphadenitis).

Eye lesions.

Eye itching, redness or swelling.

Visual impairment (partial or complete blindness).

DIAGNOSIS

Diagnosis could be done using various means. This includes:

Clinical presumptive diagnosis is made if the patient lives or visits areas where the disease is endemic and has a characteristic skin or eye changes described above.

Definitive diagnosis is simply done by seeing adult worms in excised skin nodules, eye lesion or by finding microfilariae in skin shaving or punch biopsis of the skin.

In addition, an immunological test for antibodies developed against the parasites earlier before the infection, is useful to determine if a person is infected.

TREATMENT FOR ONCHOCERCIASIS

Treatment is done by giving the patient ivermectin, an anti-parasitic drug once or twice per year for about 10-15 years (the lifespan of the adult worms).

Despite the fact, that ivermectin drug has been shown to be effective in killing the microfilariae,it is ineffective against the adult worms. Most clinicians recommend that subcutaneous nodules should be excised, thereby removing the adult worms that may reproduce more microfilariae over time. Though there is a promising new treatment using Doxycycline that kills the adult worms by killing the wolbachia bacteria on which the adult worms depend for survival.

PREVENTION AND CONTROL

There are no medications available to protect someone from becoming infected with Onchocerca volvulus. The best way to stay safe includes protective measures against bites from the insect. This includes:

Wearing insect repellent on exposed skin,

Wearing long sleeves shirts and long trousers during the day when blackfly bites,

Wearing permethrin treated clothing. Permethrin is an insect repellent that can be impregnated into clothes. This provides further protection against blackfly bites.

Though, there are promising prospect to the complete elimination of onchocerciasis from the world, which is possible. Nevertheless, Let us stay safe by protecting ourselves, as we look forward to the moment that the world will be free from the disease.

Reviewed on 16/04/2020

REFERENCES
World Health Organization – Information on Onchocerciasis

http://www.who.int/apoc/publications/en/

http://www.mectizan.org/resources?type=Document

https://www.cdc.gov/parasites/onchocerciasis/treatment.html

https://www.who.int/news-room/fact-sheets/detail/onchocerciasis

United States. Centers for Disease Control and Prevention. “Parasites — Onchocerciasis (also known as river blindness).” Aug. 10, 2015. <http://www.cdc.gov/parasites/onchocerciasis/>.

United States. Centers for Disease Control and Prevention. Cantley, P. “Onchocerciasis (river blindness).” July 10, 2015. <http://wwwnc.cdc.gov/travel/yellowbook/2016/infectious-diseases-related-to-travel/onchocerciasis-river-blindness>.

World Health Organization. Onchocerciasis: Key facts WHO, Geneva 2018 Accessed 1 February, 2019 [updated 4 April 2018] http://www.who.int/news-room/fact-sheets/detail/onchocerciasis.

Dadzie Y, Amazigo UV, Boatin BA, Seketeli A. Is onchocerciasis elimination in Africa feasible by 2025: a perspective based on lessons learnt from the African control programmes. Inf Dis Poverty. 2018;7(1):63.