Onchocerciasis (River Blindness) 1: the parasite, vector, disease and treatment

Published on January 30, 2020   34 min

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Hello. My name is Adrian Hopkins. We're going to look at onchocerciasis or river blindness. My experience has been mostly in Africa where river blindness is a major disease. But in the last few years, I've been director of the Mectizan Donation Program which has been the strategy we have used distributing mectizan to control the disease. The first part of the talk is going to concentrate on the parasite, the vector, the disease manifestations, and the treatment; for the second part of the talk, we'll concentrate on control and hopefully, the elimination of transmission.
This slide shows a picture of a lady who lives in South Sudan in a community called Awadi. In this community, there are around 5,000 people, but of that community, 800 are blind or severely visually impaired. This disease is transmitted because people live near the river. You can see from the photo just a small tributary of the River Nile, which is where Awadi is situated. We have to remember that small rivers like this are the source of water for all of the daily living that people have to do, washing, this is where children come and play, sometimes that's the only source of water. So, people can't get away from this particular problem if they are just living geographically close to the river.
What is onchocerciasis? Well, it's a parasitic disease which is caused by a filaria, which is like a long thin worm. The filaria is called Onchocerca volvulus. Volvulus implies what we will see shortly, with all the females that tend to stick together, tied up in a knot, which is where the word volvulus comes from, and which is where the adults live in what we call nodules, or sometimes you'll see them written as Onchus sarcoma. The adult females produce many many larvae every single day, thousands of larvae every day. These are mobile and they move through the skin and some also get into the eyes and some possibly get into some of the other tissues of the body, around the brain and other parts of the body. While the microfilariae or the larvae are alive, they don't cause too many problems. But after six months to a year, if they haven't been swallowed by the vector, which we'll come to in a minute, they will start dying. Every microfilaria that dies creates a little bit of inflammation around it as it dies; it's not much of a problem if it's just one or two but if thousands are produced every day, then thousands are going to be dying every day, and this is what gives the major inflammatory changes that we see in the disease. As I said, the filaria is transmitted by a small black fly, it's one of the Simulium species. The most common species is Simulium damnosum, which some people can describe as the damn, the black fly, which pretty much describes what it means when you get bitten by this fly. The fly needs to have a blood meal to reproduce. So, every time it lays a batch of eggs, it has to have a blood meal before that. The eggs are laid in fast-flowing water and they have little strands that stick to the vegetation or sometimes to rocks. They need well-oxygenated water. Once they're stuck on vegetation or rocks, the eggs develop into larvae and then into pupa as we'll see.

Onchocerciasis (River Blindness) 1: the parasite, vector, disease and treatment

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