Did you know that 25 million people in 30 different African and Middle Eastern countries are infected with Onchocerciasis? Do you even know what onchocerciasis is? I’m going to get off my high horse and admit that I didn’t know it was a thing until I went to an optional lecture last week. It’s one of those things that we privileged few don’t think about because it simply doesn’t affect us! This is not going to be a post about how thoughtless we all are because we haven’t googled every single neglected tropical disease that there is. That would be wrong because of course, I am one of those people that know next to nothing about these lesser known diseases.
I’ve been informed that onchocerciasis has a cure, which is great if you can get hold of it. I’ll talk about the control programs later on but first I’ll introduce you to what I’ve been told or have found out about the disease.
Onchocerciasis has thankfully been given a much more pronounceable name: River Blindness. This name also gives a clue as to the circumstances with which people become infected with it. The main cause is a parasitic worm called Onchocerca volvulus that gets transmitted to humans via the black fly which likes to bite humans and share its worms with the host; how charitable. This is definitely not one of those cases where sharing is caring! According to the World Health Organisation and my lecturer, symptoms include sever itching, accelerated aging in the skin and visual impairment which can lead to permanent blindness. This disease is connected to rivers because the black flies that transmit the worms breed in fast flowing waters such as rivers and streams. These sources of water are often located next to fertile land which is used in agriculture and home to small villages that are easy targets for this disease.
The party starts once the worm is inside the human host; larvae or microfilariae are produced by the adult worms which can be several centimetres in length! The adult chills in a lump under the skin caused by the bite (a subcutaneous nodule- lovely phrase) and sends it’s children into the body where they migrate to the host’s organs, skin and eyes. I feel like this could spark some very cool sci art. It seems that the disease is mostly caused by a symbiotic bacterium called Wolbachia which is carried by the parasitic worms and could be seen as a friend with which they share their journey. If you want to learn more about Wolbachia, I stumbled across an amusing post about it. I also found an easy-to-read journal paper that describes everything that you may want to know about this bacterium and it’s role in causing river blindness and possibly makes this blog post a bit pointless. Never mind.
Despite earlier claims that I’ve made about diseases such as this not affecting people that live in the UK, I was interested to learn that we do in fact have Onchocerciasis in this country. Here, it affects cattle and in a study that involved the investigation of 463 cattle from Wales and Cheshire, 28.5% of the animals were infected with one of three different Onchocerca species (Trees, McCall and Crozier, 1987). Quite scary considering that in developing countries, black flies can bite infected cattle and then transfer the worms to humans!
Let’s change tack and find some good news! Onchocerciasis has been eradicated in four countries, Colombia, Ecuador, Mexico and most recently Guatemala! We humans must be doing something right afterall! The main treatment for Onchocerciasis infection is Ivermectin which kills the larvae but unfortunately does nothing to remove the adults. The drug is taken for the lifespan of the adult worms which can be over six months! A new treatment is being pioneered to target that pesky Wolbachia and it involves taking doxycycline which inhibits protein synthesis and stops the bacteria from reproducing. The Onchocerciasis Control Program (OCP) helped to bring the disease under control by spraying insecticides against the larvae of the black fly vector between 1974 and 2002. Here are some quick- fire facts from WHO about all the good that the OCP has done…
- 40 million people have been relieved of their infection with the disease
- Blindness was prevented in 600,000 people
- 18 million children were born without the risk of being infected by Onchocerciasis
- 25 million hectares of abandoned land has been recolonised and the crops grown on this land was able to feed 17 million people every year!
Now if that hasn’t given you some hope as to what the human race is capable of then I don’t know what will! I feel like the best way to tackle neglected tropical diseases is to take them a couple at a time and come up with effective strategies, because of my distinct lack of knowledge about NTDs these have probably been thought up already and I’m decades behind!
So here’s to more effective disease eradication in the future!
Trees, A.J., McCall, P.J. and Crozier, S.J., 1987. Onchocerciasis in British cattle: a study of Onchocerca gutturosa and O. lienalis in North Wales. Journal of helminthology, 61(02), pp.103-113.