By, Sarah Smith
The Onchocerca volvulus is a worm that causes Onchocerciasis, also known as “River Blindness.” This nematode has a fascinating and devious way of reaching its only host, humans. They infect and then mature inside a Black fly, and when it bites a human, they are transmitted through the fly’s saliva to the host’s skin, where they reproduce in the muscle fibers. If they reach the eyes of the host, which they commonly do, they can cause permanent blindness, commonly referred to as “river blindness” in Africa.
Form and Function:
Onchocera Volvulus begins its life cycle when a female black fly drinks the blood of a human. The parasite, which is found in the dermis of the human, is consumed by the fly. The parasite then chews through the gut of the fly and relocates in the thoracic flight muscles of the fly. At this point, it is in its first larval phase. It stays there until it matures into the second larval phase, and then moves to the saliva of the fly. When the fly drinks the blood of a human host, the O. volvulus passes into its bloodstream. Next, the larvae moves to the subcutaneous tissue. Here, they form bumps, called nodules, and mature into fully developed, adult worms. This developmental period lasts between six to twelve months. Once fully matured, they mate, and can reproduce at a rate of between 1,000 to 3,000 a day. These eggs remain in the subcutaneous tissue, until picked up by a black fly, when they begin the cycle again. The adult worms, however, migrate to the skin and connective tissue of their host.
Impact on Humanity:
The Onchocerca Volvus causes a disease called Onchocerciasis. Onchocerciasis is most commonly transmitted in Guatemala, Ecuador, Mexico, Colombia, Venezuela, Brazil, Yemen, and thirty countries in Africa. People get infected when in frequent contact with black flies. Blindness almost always results from infections, as well as rashes and bumps under the skin. Onchocerciasis used to be one of the leading causes of preventable blindness and skin diseases in the word. World Health Organization, however, has dramatically reduced the impact of the disease by leading disease control programs. These programs introduce a drug called Ivermectin, which is taken orally and heals the disease entirely. Because of this being donated around the world, the impact of Onchocerciasis has dramatically decreased throughout the years. The prevention of Oncerciasis is simple: wear insect repellent. However, many countries do not have access to this. Unfortunately, there are no vaccinations yet invented that prevent the disease.
Journal/ Article Review:
This article is about the Onchocerca Volvus, and talks about how scientists have yet to create a vaccine against its infection. They have used molecular tools to identify the antigens that may help prevent development of the disease, yet are unable to come up with a vaccine to prevent the disease. This article talks about different attempts and ideas of how they can create a vaccine to prevent Onchocerciasis.
• Nettleman, Mary. "Onchocerciasis." eMedicine. N.p., 04/16/2009. Web. 13 Oct 2010
• "Onchocerciasis (River Blindness)." Medic8. N.p., 09/11/2004. Web. 13 Oct 2010
• "Neglected Tropical Diseases." Plos. The Onchocerca volvulus Cysteine Proteinase Inhibitor, 11/18/2009. Web. 13 Oct 2010.
Photos Retrieved From:
• "Onchocerca Volvus Lifecycle." Wikipedia. Wikipedia Commons, n.d. Web. 14 Oct 2010.
• Cummings, Varki. "Nematoda." Essentials of Glycobiology. The Consortium of Glycobiology Editors, 2009. Web. 14 Oct 2010. http://www.google.com/imgres?imgurl=http://www.ncbi.nlm.nih.gov/bookshelf/picrender.fcgi%3Fbook%3Dglyco2%26part%3Dch23%26blobname%3Dch23f1