A trio of scientists earned the 2015 Nobel Prize for Medicine on Monday for unlocking revolutionary treatments for malaria and roundworm, helping to roll back two parasitic diseases that blight millions of lives.

Tu Youyou of China won half of the award for her work in artemisinin, a drug based on ancient Chinese herbal medicine, the Nobel jury announced. She is the first Chinese woman national to win a Nobel Prize in science.

Irish-born William Campbell and Satoshi Omura of Japan shared the other half for an anti-roundworm treatment dubbed avermectin, derived from soil-dwelling bacteria.

"These two discoveries have provided humankind with powerful new means to combat these debilitating diseases that affect hundreds of millions of people annually," the Nobel committee said.

"The consequences in terms of improved human health and reduced suffering are immeasurable."

Tu, 84, has been chief professor at the China Academy of Traditional Chinese Medicine since 2000.

She conducted research in the 1970s, at the height of China's Cultural Revolution, that led to the discovery of artemisinin, a drug that has slashed the number of malaria deaths.

The treatment is based on traditional medicine -- a herb called sweet wormwood or Artemisia annua.

Artemisinin-based drugs are now the standard combination for treating malaria since the mosquito-transferred Plasmodium parasite developed resistance to other drug types like chloroquine.

According to the World Health Organization (WHO), there were about 198 million malaria infections in 2013 and 584,000 deaths -- most of them African children.

The other half of the prize honoured Omura and Campbell for "a new class of drugs with extraordinary efficacy against parasitic diseases," the Nobel statement said.

Registered drugs derived from avermectin "have radically lowered" the incidence of river blindness and elephantiasis, both caused by parasitic worms, it added.

River blindness, also known as onchocerciasis, is caused by a worm transmitted to humans through the bites of infected blackflies. Its symptoms include disfiguring skin conditions and visual impairment, including permanent blindness.

More than 99 percent of those affected live in Africa.

Elephantiasis or lymphatic filariasis, is a mosquito-borne infection which causes grotesque and disfiguring swelling of the limbs.

Omura, a microbiologist, isolated new strains of a group of bacteria called Streptomyces, and successfully cultured them in the lab.

Campbell, a research fellow emeritus at Drew University in New Jersey in the United States, was born in 1930 in Ramelton, Ireland.

His role was to show that a component from one of Omura's cultures was active against parasites -- this became avermectin.

"I humbly accept the prize," 80-year-old Omura, a professor emeritus at Kitasato University, said in a interview with the Nobel Foundation.

He thanked the "many, many researchers" who had contributed to his findings, saying he was "very, very lucky."

The Swedish news agency TT said the Nobel Foundation had not yet been able to reach Tu and Campbell to inform them of their prizes.

This year's Nobel laureates will share the prize sum of eight million Swedish kronor (about $950,000 or 855,000 euros).

Last year, the medicine prize went to British-American researcher John O'Keefe and a Norwegian couple, Edvard and May-Britt Moser, for discovering the brain's "inner GPS" that helps people navigate.

The Nobel awards week continues with the announcement of the prize for physics on Tuesday, chemistry on Wednesday and literature on Thursday.

The peace prize will be awarded in Oslo on Friday, with the economics prize wrapping up the Nobel season next Monday.

The laureates will receive their prizes at a formal ceremony in Stockholm on December 10, the anniversary of the 1896 death of the creator of the award, Alfred Nobel, a Swedish philanthropist and scientist.

A separate ceremony is held for the peace prize on the same date in Oslo.