Credit: BOSTON GLOBE/CONTRIBUTOR/GETTY
Credit: YOSHIKAZU TSUNO/STAFF/GETTY
Credit: CHINAFOTOPRESS/ CONTRIBUTOR/GETTY

The discovery of two medicines that have — in the words of the Nobel Assembly at Karolinska Institutet — “revolutionized the treatment of parasitic diseases” has resulted in the award of the 2015 Nobel Prize in Physiology or Medicine to William C. Campbell, Satoshi Ōmura and Youyou Tu (pictured top to bottom). Parasitic diseases affect a huge number of people, but they are more common in the poorest parts of the world. Campbell and Ōmura were jointly awarded half of the prize for their work on a therapy against infections caused by roundworms. The other half of the prize was awarded to Tu for her discovery of a new therapy against malaria.

Ōmura, from Kitasato University, Japan, is an expert in culturing bacteria and isolating the chemical compounds they produce. He isolated new strains of Streptomyces — a group of soil-dwelling bacteria well-known for producing antibacterial compounds — that showed promising activity against harmful microorganisms. He gave these strains to a team led by Campbell — an expert in parasite biology who was then working at the Merck Institute for Therapeutic Research in Rahway, New Jersey, USA. Campbell was able to implicate avermectins as partially responsible for the antiparasitic activity. Development of this series of compounds led to the production of the drug ivermectin, which is used to treat onchocerciasis (widely known as river blindness) and lymphatic filariasis (which causes elephantiasis).

Youyou Tu led a research program to identify bioactive compounds from traditional Chinese medicines. Their search for antimalarial compounds — motivated by the increasing ineffectiveness of quinine and chloroquine — eventually led to the isolation of artemisinin from the wormwood plant (Artemisia annua). Like many bioactive natural products, isolating sufficient material from the plant can be problematic. Therefore most artemisinin is now produced by a semi-synthetic method: the unusual peroxide structure — thought to be responsible for the drug's mechanism of action — is introduced by a chemical oxidation of artemisinic acid, which is itself produced by a specially engineered strain of yeast.