The impact of Neglected Tropical Diseases on Universal Eye Health

By Professor Alan Fenwick of Imperial’s Schistosomiasis Control Initiative (SCI)

‘Oncho blind’ – 60 years ago blind older people were led by children

There are five neglected tropical diseases (NTDs) which are the scourge of Africa, the Indian sub-continent, the Far East and South America.  Onchocerciasis is one of these 5 and until the late 20th century caused millions of people to gradually lose their sight and eventually go blind. The parasite is spread by infected Simulium blackflies which when they bite a human, transfer microscopic larvae to the human host, where they develop into adult worms and females produce millions of new larvae during their lifetime. It is these larvae that are the cause of irreversible blindness in as many as 25% of the adult population in several countries in Africa. Onchocerciases was also prevalent in some countries in South America.

Another cause of blindness in the poorest populations globally is the NTD trachoma. Caused by certain subtypes of the Chlamydia infection, it is spread through contact with discharge from the eyes or nose of an infected person. In developing countries, eye-seeking flies are a major cause of transmission, particularly in areas where water to wash is in short supply.

trachoma flies
‘Trachoma flies’ – After conjunctivitis eyelashes scratch the cornea causing blindness.

The remaining three major NTDs, schistosomiasis, lymphatic filariasis and soil-transmitted helminths do not directly affect eye health but overlap geographically with onchocerciasis and trachoma and debilitate in other harmful ways.

All 5 of these NTDs can be controlled by the annual administration of safe oral medications. Onchocerciasis, and the resulting blindness and itching caused by the larvae are controlled by an annual dose of Mectizan (Ivermectin). Trachoma is controlled by an annual does of Zithromax, and schistosomiasis is controlled by an annual dose of praziquantel. Albendazole treats both lymphatic filariasis and soil-transmitted helminths. All four medications are generously donated by the pharmaceutical companies which manufacture them (Merck Sharp Dom, Pfizer, E.Merck and GSK respectively). In 2015 almost 1 billion individuals globally have benefitted from treatment directly resulting from these donations.

The good news from South America is that onchocerciasis has been eliminated in Colombia, Ecuador and Guatemala. In Africa, Mectizan has been delivered to over 100 million people every year since 1987, resulting in transmission having been almost stopped, and even more importantly cases of blindness caused by onchocerciasis being a rarity in Africa thanks to the effects of these annual treatments.

‘Trachoma’ – Flies carry Chlamydia which cause conjunctivitis.

As for trachoma, Pfizer are delivering over 70 million doses of Zithromax to affected countries and the target has been set to eliminate trachoma by 2020. Interestingly, Ethiopia has almost 30% of all cases of trachoma in the world, and a concentrated programme has started to reach all the people infected in that country.

Thus the World Health Organisation’s coordination of a global NTD programmes has virtually eliminated blindness caused due to either onchocerciasis and trachoma.

As Director of the Schistosomiasis Control Initiative (SCI) based at Imperial College London, we have assisted many countries in Africa since 2002 to treat and control both schistosomiasis and soil transmitted helminths (intestinal worms).  Efforts to reduce schistosomiasis (a trematode worm which causes anaemia, and bladder and liver fibrosis) have been less satisfactory than onchercerciasis and trachoma. With 250 million people infected in Africa, enough medication (praziquantel) is donated to treat 100 million children every year, however the funding to deliver these tablets is in short supply. In 2015 there were only sufficient funds to enable around 65 million treatments to be delivered. An increase in funding for treatment delivery is needed to effectively and efficiently use the donation from E. Merck.

In summary, the control of blindness due to onchocerciasis and trachoma is well on track for elimination by 2020, but for schistosomiasis 2030 is a more realistic target.

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