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Onchocerciasis

Written by Maddie Rice, Peer Reviewed by Emily Bengel, Edited by Courtney Coleman

 

Background

Neglected diseases are a set of illnesses that suffer from a lack of research and attention from world health organizations, resulting in limited access to effective prevention and treatment options. Untreated, neglected diseases can have significant impacts on impoverished people, and despite being an urgent issue, addressing such diseases has only recently started to gain traction, although not nearly at the pace needed to combat disease burden. Onchocerciasis, also known as river blindness, is one of these neglected diseases that primarily affects communities in rural, agricultural areas of sub-Saharan Africa.


Transmission

Onchocerciasis is caused by the parasitic worm Onchocerca volvulus and transmitted to humans through the bite of blackflies that inhabit streams and rivers. This environment lets the larvae filter more water and ingest more food as the water rapidly flows (1).


Risk Factors

Onchocerciasis is most common in sub-Saharan Africa, with ninety percent of cases being found in the region; however, cases have also been discovered in Yemen and in parts of Latin America (1,4). Risk of disease is greater if a person is frequently near fast-flowing streams or rivers. In certain parts of Africa, since multiple bites are required for the infection to spread, individuals who reside in these regions are at the highest risk, and it is uncommon for travelers to become infected with Onchocerca volvulus if they are only in the area for a short amount of time (7).


Statistics

Currently, there are 18 million people in the world who are living with onchocerciasis (5), of which 270,000 have

permanent vision loss. Positively, the number of these individuals receiving treatment is increasing, as shown in Figure 1 (5). This graph shows that, over the course of 15 years, the number of people getting treatment increased from about one million to 17 million.


Symptoms

People who have been infected with onchocerciasis may experience symptoms such as disfiguring skin conditions, severe itching, and visual impairment,

including permanent blindness. It is also common for nodules under the skin to form around the adult worms.

Additionally, one may experience swollen lymph nodes, bumps under their eyes, or the inability to

distinguish certain colors, which is shown in Figure 2 (3). These symptoms are a result of the minuscule parasites known as microfilariae, which travel throughout the human body in the subcutaneous tissue, and trigger severe inflammatory reactions when they die (1,4,7).


Diagnosis and Treatment

Onchocerciasis can be diagnosed using a variety of procedures. A clinician will usually start by feeling a potentially infected person's skin to look for nodules. Then, a skin biopsy will be performed in which a 2- to 5-milligram sample of the skin is taken for testing. If the person is experiencing infection, the infectious larvae will emerge from the tissue when the biopsy is submerged in a saline solution. Six snips are typically made from various locations on the body (7). To treat infection, the World Health Organization recommends ivermectin at least once per year for 10-to-15 years after infection, although some effects of the disease are permanent, such as blindness, as previously stated above (1).


Conclusion

Onchocerciasis is a neglected disease that needs more recognition, despite recent increases in available treatments for those infected. Although it is a problem only in select parts of the world, onchocerciasis affects millions of people, and it is not something to be taken lightly due to its severe symptoms and risk of permanent blindness. In order to eliminate onchocerciasis, more research and funding is urgently needed.

 

Works Cited


(1) “CDC - Onchocerciasis - Epidemiology & Risk Factors.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 9 Sept. 2019,

https://www.cdc.gov/parasites/onchocerciasis/epi.html#:~:text=The%20main%20burden%20is%2 0in,Yemen%20in%20the%20Middle%20East


(2) “National Library of Medicine (NLM).” National Institutes of Health, U.S. Department of Health and Human Services, 6 Apr. 2020,

https://www.nih.gov/about-nih/what-we-do/nih-almanac/national-library-medicine-nlm


(3) “Onchocerciasis (African River Blindness).” EyeWiki, 21 Dec. 2022,

https://eyewiki.aao.org/Onchocerciasis_%28African_River_Blindness%29


(4) “Onchocerciasis (River Blindness).” World Health Organization, World Health Organization, https://www.who.int/news-room/fact-sheets/detail/onchocerciasis


(5) “Onchocerciasis - ‘River Blindness.’” PAHO/WHO | Pan American Health Organization, https://www.paho.org/en/topics/onchocerciasis-river-blindness#:~:text=Symptoms%20include%20severe%20itching%2C%20disfiguring,and%20270%2C000%20blinded%20by%20onchocercias is


(6) “Onchocerciasis.” DermNet,

https://dermnetnz.org/topics/onchocerciasis


(7) Stewart, Dava. “Onchocerciasis (River Blindness): Symptoms, Causes, and More.” Healthline, Healthline Media, 17 Aug. 2018,

https://www.healthline.com/health/onchocerciasis-river-blindness

 

This post is not a substitute for professional advice. If you believe that you may be experiencing a medical emergency, please contact your primary care physician, or go to the nearest Emergency Room. Results from ongoing research is constantly evolving. This post contains information that was last updated on April 21, 2023.

 

Maddie Rice is currently a Molecular & Cell Biology major undergraduate at UC Berkeley.


Emily Bengel is a 2nd year Ph.D. student in Epidemiology at the University of Washington.


Courtney Coleman is a master's degree candidate in biology at Harvard and Co-President of Students vs Pandemics.

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