Three scientists from Ireland, Japan and China have won the Nobel prize in medicine for discoveries that helped doctors fight malaria and infections caused by roundworm parasites.

The judges in Stockholm awarded the prize to William C Campbell, Satoshi Ōmura and Youyou Tu – the first ever Chinese medicine laureate.

Campbell and Ōmura were cited for discoveries concerning a novel therapy against infections caused by roundworm parasites, while Tu was rewarded for discoveries concerning a novel therapy against malaria.

“The two discoveries have provided humankind with powerful new means to combat these debilitating diseases that affect hundreds of millions of people annually,” the committee said. “The consequences in terms of improved human health and reduced suffering are immeasurable.”

Ōmura made his discovery after collecting soil samples from around Japan and isolating bacteria called Streptomyces. One of them was Streptomyces avermitilis, which became the source for the drug avermectin.

Ōmura’s work was taken up by Campbell, who showed that Streptomyces avermitilis was remarkably effective at killing off parasites in domestic and farm animals. The compound responsible, avermectin, was modified into a more effective substance called ivermectin. When tested in humans, the compound was found to have killed off parasite larvae.

Meanwhile, working in China, Tu was searching through herbal remedies in the hope of finding new leads for malaria treatments. She found that an extract from the plant Artemisia annua was sometimes effective, but the results were inconsistent. After more research, she hit on the active compound in the plant, a chemical that became known as artemisinin, a new class of antimalarials that kill malaria parasites at an early stage of development.

The New Scientist ran a lengthy profile of Tu – the 12th woman to win the medicine prize – shortly after she won the Lasker prize in 2011. Tu was part of a secret drug discovery project set up by Mao Zedong in 1967 known only as Project 523. She was sent to Hainan province to see the impact of malaria for herself, meaning she had to leave her daughter behind at a local nursery. When she came back she says her daughter did not recognise her.

“The work was the top priority, so I was certainly willing to sacrifice my personal life,” she said. “I saw a lot of children who were in the latest stages of malaria. Those kids died very quickly.”

The medicine award was the first Nobel prize to be announced. The winners of the physics, chemistry and peace prizes are set to be announced later this week. The economics prize will be announced next Monday. No date has been set yet for the literature prize, but it is expected to be announced on Thursday.

Associated Press contributed to this report