Onchocerciasis
“River Blindness”
http://www.unep.org/yearbook/2004/images/emergingphoto5.jpg
Onchocerciasis
“River Blindness”
Second leading infectious cause
of blindness in the world
http://www.unep.org/yearbook/2004/images/emergingphoto5.jpg
Onchocerciasis
“River Blindness”
Second leading infectious cause
of blindness in the world
Also causes skin lesions
and skin nodules and
intense itching
http://www.unep.org/yearbook/2004/images/emergingphoto5.jpg
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
Adult worms
http://www.icp.ucl.ac.be/~opperd/parasites/images/worms.jpg
http://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htm
Microfilariae of O. volvulus from a skin
nodule of a patient from Zambia
Infection spreads from person to
person by the bite of an infected
Simulium blackfly
WHO/TDR/Stammers
Human Stages
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
Blackfly Stages
5. After ingestion,
microfilariae migrate to
the thoracic muscles of
the blackfly
Blackfly Stages
6. There they develop
into stage 1 larvae, and
then stage 3 larvae
5. After ingestion,
microfilariae migrate to
the thoracic muscles of
the blackfly
Blackfly Stages
7. 3rd stage larvae can
infect another human
when the blackfly takes
a blood meal
6. There they develop
into stage 1 larvae, and
then stage 3 larvae
5. After ingestion,
microfilariae migrate to
the thoracic muscles of
the blackfly
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
The infected area becomes
increasingly opaque with
more microfilariae
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
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 populations
2.Use Ivermectin to treat infected people
Controlling blackfly populations involved interrupting
transmission by eliminating the blackfly vector
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
Controlling blackfly populations involved interrupting
transmission by eliminating the blackfly vector
Helicopters are
used to spray
insecticides on
rivers and fast
moving waters
(Simulium
breeding sites)
http://www.icp.ucl.ac.be/~opperd/parasites/onch1.html
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
References
Diawara 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>.