The Nobel Prize for Medicine has been awarded to three scientists for their work on parasites. While they might not appear to have the most glamorous of professions, these researchers are (until now) unsung heroes whose work has improved lives of millions of people around the world.
The prize is shared by Ireland’s William C Campbell and Japan’s Satoshi Ōmura for their work that produced a drug to kill the all-too-common roundworms that are found in the guts of humans and animals and can carry a variety of potential lethal diseases; and China’s Tu Youyou, who discovered a drug that kills the parasite responsible for malaria and now helps combat the disease around the world.
Parasites are living organisms that live in or on the bodies of other organisms. Humans can host about 400 different parasites, including worms, protozoa and arthropods. Some of these are relatively harmless such as common headlice or pinworms, but others carry disease and some, such as the malaria parasite, can kill directly.
Roundworms include a huge variety of species that live inside human and animal digestive systems, eating the food we consume and sometimes making us very ill. They affect the young in particular, as all their food needs to go to growing a healthy body not feeding intestinal worms. Other types of roundworm cause diseases such as onchocerciasis – also known as river blindness – and lymphatic filiariasis, which leads to the horrific swelling of the leg and foot or scrotum known as elephantiasis.
Campbell and Ōmura discovered a compound called avermectin, which was later modified to create ivermectin. Today this cheap and effective drug is being used to treat the millions at risk of these diseases. The drug works by paralysing the worms’ nerve cells and ultimately killing them, but is ineffective against the nerve cells in mammals and doesn’t cross from the blood into the brain, making it suitable for human treatment.
Ivermectin is also widely used throughout the world as a wormer for livestock. Grazing animals such as sheep, cattle and horses, get infected with worms by picking up the eggs or larvae from grass that has been contaminated with dung from other infected animals.
The Roll Back Malaria campaign recently celebrated a 60% fall in deaths from malaria from an estimated million deaths per year at the turn of this century, mostly in children under five. But malaria remains a significant health problem in many of the world’s poorest countries. About half the world’s population – an estimated 3.2 billion people – are at risk from malaria and there are about 200 million cases of the disease every year.
The malaria parasite is far smaller than the roundworm. This microscopic organism lives inside the red cells in the blood and multiplies by causing them to burst open and releasing more parasites to invade other red cells. This provokes the characteristic fevers and chills of malaria but can ultimately lead to death.
Tu Youyou discovered the malaria drug artemisinin from a plant known as Artemisia annua or sweet wormwood that was used in ancient Chinese herbal medicine to treat fever. It kills the malaria parasite inside the red cells, although exactly how is still unknown. It is now widely used together with other drugs in artemisinin combination therapy (ACT) to treat malaria, with some research showing it can reduce death rates by as much as 35% compared to other treatments such as quinine.
Artemisinin use has been limited by the supply of the plant it is extracted from but the pharmaceutical company Sanofi recently developed a way of synthesizing the drug from genetically engineered yeast. This has raised hopes of increasing the world supply and potentially lowering the cost of this very important drug.