Onchocerciasis “River Blindness”

Onchocerciasis “River Blindness” Second leading infectious cause of blindness in the world

Onchocerciasis “River Blindness” 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

Transmission is concentrated in central Africa and Latin America Over 90% of all cases occur in Africa

Infection caused by the parasitic worm Onchocerca volvulus 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. 3 rd stage larvae can infect another human when the blackfly takes a blood meal Blackfly Stages

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

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…

…and skin rashes and lesions, known as “leopard skin”

Others migrate to the surface of the cornea, causing sclerosing Keratitis to occur

Others migrate to the surface of the cornea, causing sclerosing Keratitis to occur The infected area becomes increasingly opaque with more microfilariae

Ivermectin is the drug of choice for Onchocerciasis Paralyzes and kills microfilariae of O. volvulus

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

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

Studies in hyperendemic foci have shown the effectiveness of Ivermectin

Has anyone done anything about this?

Onchocerciasis Control Programme (OCP) was launched in 1974 Launched by WHO

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

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 )

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: /journal.pntd "DPDx - Filariasis." DPDx – Filariasis. Web. 05 Nov "Onchocerciasis (River Blindness)." Stanford.edu. Web. 05 Nov "Priority Eye Diseases." WHO. Web. 05 Nov