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River blindness: saving the sight of billions with animal medicines

The discovery of ‘wonder drug’ ivermectin has been hailed as arguably one of the biggest discoveries alongside penicillin and aspirin. But it had humble beginnings, starting life as a parasiticide in livestock.

Now, following a program to make the medicine available free of charge to those at risk of river blindness, the treatment has been administered 2.9 billion times, saving the sight of scores of people.   We take a look at the story behind the discovery and how animal health played a key role in breaking new ground for human health.

What is river blindness? 

River blindness is a debilitating parasitic disease in humans which causes intense skin itching and can lead to irreversible loss of sight. Spread by black flies infected by the parasite, the disease affects many of the world’s poorest people, often farmers, living close to riverside areas. 

The flies transfer parasite larvae when they bite humans, they then grow into worms which produce thousands of offspring every day. When these larvae die, they cause a reaction in the body, which can lead to blindness.

At the time of discovery, onchocerciasis (as the condition is formally known) was one of the leading causes of preventable blindness worldwide, affecting 18 million people in West Central Africa, the Middle East and South America. 

How did scientists make their discovery? 

Dr William Campbell and Professor Satoshi Ōmura – who were awarded the Nobel Prize for Physiology/Medicine in 2015 – modestly described the method of discovering the drug as “simple”.  Their teams worked to find unfamiliar microbes and understand their properties, which led to uncovering a potent new class of antiparasiticide. This was harnessed to create an animal parasiticide used to kill external and internal parasites in livestock and pets. 

Ivermectin can be used to help prevent heartworm in dogs, while it’s also effective against roundworms, mites and even ticks. It has been particularly powerful in Brazil where 80% of cattle were infested with ticks, leading to losses of $2 billion annually.  Now it is used to treat billions of animals globally, boosting food production.

How is it used in people?

It was this research which provided scientists with the confidence to believe in a human application and in 1988, the first treatment was given to a person. It works by killing young larvae and reduces the fertility of adult worms. 

Ivermectin is used to treat many different worm infections in humans but it’s River Blindness in which it has provided a lifeline for millions. 

But the story doesn’t stop there, ivermectin was also found to be effective at treating a condition called lymphatic filariasis (LF), also known as elephantiasis. This disfiguring disease affects more than 1.3 billion people, causing swollen limbs and fissured skin. In many countries, the two diseases often coexist.

Could there be a world without River Blindness?

The breakthrough was so significant that in an unprecedented move the drug-makers worked with the World Health Organization, the World Bank and others in an extraordinary public-private partnership to provide the drug free of charge to those at risk of both diseases. 

Thirty years on and their commitment, “as much as needed, for as long as needed” remains. In fact, four countries in Latin America have been officially verified as free from river blindness. While Togo is the first country in Africa to be declared free from LF and 11 more countries no longer need treatment.  

Scientists are now searching for a treatment which would block infection altogether, by killing adolescent worms immediately. One again a veterinary drug – closantel, which kills liver parasites in cattle – could hold the answer to this human health issue and potentially lead to a future without these diseases. 

Read on for more examples of how animal medicine has led to human health breakthroughs