Onchocerciasis “River Blindness”

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 Africahttp://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>.