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Onchocerciasis“River Blindness”
http://www.unep.org/yearbook/2004/images/emergingphoto5.jpg
Onchocerciasis“River Blindness”
http://www.unep.org/yearbook/2004/images/emergingphoto5.jpg
Second leading infectious cause of blindness in the world
Onchocerciasis“River Blindness”
http://www.unep.org/yearbook/2004/images/emergingphoto5.jpg
Second leading infectious cause of blindness in the world
Also causes skin lesions and skin nodules and intense itching
More than 30 million people worldwide are infected with Onchocerciasis
http://www.stanford.edu/class/humbio103/ParaSites2004/Onchocerciasis/worldmap.png
Transmission is concentrated in central Africa and Latin America
Over 90% of all cases occur in Africa
http://www.stanford.edu/class/humbio103/ParaSites2004/Onchocerciasis/worldmap.png
Infection caused by the parasitic worm Onchocerca volvulus
http://www.icp.ucl.ac.be/~opperd/parasites/images/worms.jpghttp://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htm
Microfilariae of O. volvulus from a skin nodule of a patient from Zambia
Adult worms
Infection spreads from person to person by the bite of an infected Simulium blackfly
WHO/TDR/Stammers
1. Infected blackfly introduces third stage larvae onto the skin of the host, then they penetrate the skin
Human Stages
1. Infected blackfly introduces third stage larvae onto the skin of the host, then they penetrate the skin
2. Larvae develop into adults in subcutaneous tissue
Human Stages
3. Adults produce microfilariae
Human Stages
3. Adults produce microfilariae
4. A blackfly ingests microfilariae during blood meal
Human Stages
5. After ingestion, microfilariae migrate to the thoracic muscles of the blackfly
Blackfly Stages
5. After ingestion, microfilariae migrate to the thoracic muscles of the blackfly
6. There they develop into stage 1 larvae, and then stage 3 larvae
Blackfly Stages
5. After ingestion, microfilariae migrate to the thoracic muscles of the blackfly
6. There they develop into stage 1 larvae, and then stage 3 larvae
7. 3rd stage larvae can infect another human when the blackfly takes a blood meal
Blackfly Stages
But…how does this cause blindness and other symptoms?
But…how does this cause blindness and other symptoms?
As mentioned earlier, adult worms produce microfilariae in the human stages
3. Adults produce microfilariae– up to 1000 per day!
Microfilariae induce intense inflammatory responses, especially upon their death
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
Microfilariae induce intense inflammatory responses, especially upon their death
Some microfilariae will migrate throughout the upper layers of the skin, causing large nodules to form under skin…
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
…and skin rashes and lesions, known as “leopard skin”
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
Others migrate to the surface of the cornea, causing sclerosing Keratitis to occur
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
Others migrate to the surface of the cornea, causing sclerosing Keratitis to occur
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
The infected area becomes increasingly opaque with more microfilariae
Ivermectin is the drug of choice for Onchocerciasis
• Paralyzes and kills microfilariae of O. volvulus
http://3.bp.blogspot.com/-V4h6xT_GaKM/TwcIXiInfaI/AAAAAAAAuAg/Yx6UAxhqif0/s1600/Merck-%2526-Co-Logo.jpg
Ivermectin is the drug of choice for Onchocerciasis
• Paralyzes and kills microfilariae of O. volvulus• Doesn’t kill adult females, but prevents them
from producing any offspring
http://3.bp.blogspot.com/-V4h6xT_GaKM/TwcIXiInfaI/AAAAAAAAuAg/Yx6UAxhqif0/s1600/Merck-%2526-Co-Logo.jpg
Ivermectin is the drug of choice for Onchocerciasis
• Paralyzes and kills microfilariae of O. volvulus• Doesn’t kill adult females, but prevents them
from producing any offspring– Thus, prevents transmission
http://3.bp.blogspot.com/-V4h6xT_GaKM/TwcIXiInfaI/AAAAAAAAuAg/Yx6UAxhqif0/s1600/Merck-%2526-Co-Logo.jpg
Studies in hyperendemic foci have shown the effectiveness of Ivermectin
Has anyone done anything about this?
Has anyone done anything about this?
Onchocerciasis Control Programme (OCP) was launched in 1974
• Launched by WHO
http://www.who.int/blindness/partnerships/onchocerciasis_OCP/en/index.html
Goals of OCP
1.Control blackfly populations2.Use Ivermectin to treat infected people
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
Controlling blackfly populations involved interrupting transmission by eliminating the blackfly vector
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
Helicopters are used to spray insecticides on rivers and fast moving waters (Simulium breeding sites)
Controlling blackfly populations involved interrupting transmission by eliminating the blackfly vector
OCP was a huge success and ended in 2002
African Programme for Onchocerciasis Control (1995)
Onchocerciasis Elimination Programme for the Americas (1992)
http://ars.els-cdn.com/content/image/1-s2.0-S1471492201021122-gr1.jpg
ReferencesDiawara L, Traoré MO, Badji A, Bissan Y, Doumbia K, et al. (2009) Feasibility of Onchocerciasis Elimination with Ivermectin Treatment in Endemic Foci in Africa: First Evidence from Studies in Mali and Senegal. PLoS Negl Trop Dis 3(7): e497. doi:10.1371/journal.pntd.0000497
"DPDx - Filariasis." DPDx – Filariasis. Web. 05 Nov. 2012. <http://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htm>.
"Onchocerciasis (River Blindness)." Stanford.edu. Web. 05 Nov. 2012. <http://www.stanford.edu/class/humbio103/ParaSites2004/Onchocerciasis/index.htm>.
"Priority Eye Diseases." WHO. Web. 05 Nov. 2012. <http://www.who.int/blindness/causes/priority/en/index3.html>.