Two French scientists who discovered the HIV virus and a German who found the virus that causes cervical cancer have been awarded the 2008 Nobel prize for medicine.
Luc Montagnier, director of the World Foundation for AIDS Research and Prevention, and Prof Francoise Barré-Sinoussi of the Institut Pasteur won half the prize of 10m Swedish kronor (€1,024,427) for discovering the HIV virus.
AIDS has killed millions of people since it was first identified in the 1980s.
Harald zur Hausen of the University of Duesseldorf was awarded the other half of the prize for work that went against the then current dogma as to the cause of cervical cancer.
'The three laureates have discovered two new viruses of great importance and the result of that has led to an improved global health,' said Jan Andersson, a member of the Nobel Assembly at Sweden's Karolinska Institute.
The award, however, has revived a long-running dispute between the two French scientists and Dr Robert Gallo of the US National Cancer Institute over who discovered and identified the virus.
It eventually took a meeting of two presidents - Jacques Chirac of France and Ronald Reagan of the US - to persuade the National Institutes of Health and the Institut Pasteur to share royalties for the discovery and for the two researchers to agree to share the credit in 1987.
When Dr Montagnier and Dr Francoise Barré-Sinoussi began their research in the early 1980s, a hitherto undocumented immune deficiency syndrome began striking down victims in the west.
The institute said the French researchers isolated and cultured cells from patients with swollen lymph nodes characteristic of the early stage of acquired immune deficiency.
By 1984, they had obtained samples of the retrovirus from a variety of people. These included people who had been infected from sexual contact, haemophiliacs, patients who had received blood transfusions and infants who had contracted the disease from their mothers.
The researchers found the virus infected and killed lymphocytes from both diseased and healthy donors and reacted with antibodies from infected patients.
Their findings also helped explain how HIV impaired the immune system.
Harald zur Hausen was recognised for research based on his idea that oncogenic human papilloma virus, or HPV, caused cervical cancer, the second most common cancer among women.
Dr zur Hausen, who began his research in the 1970s, assumed that if HPV was causing the cancer it should be possible to detect it by searching tumour cells for a specific viral DNA.
For 10 years, he searched for different human papilloma virus types, detecting them in cervix cancer biopsies. The virus types he found, and later cloned, are found in about 70% of cervical cancer biopsies around the world.
'More than 5% of all cancers worldwide are caused by persistent infection with this virus,' the Nobel assembly said.
An estimated 500,000 women are diagnosed with the disease each year and about 300,000 die from it, mostly in the developing world. Merck & Co's Gardasil and GlaxoSmithKline's Cervarix are vaccines that protect against some strains of the virus.
Medicine is traditionally the first of the Nobel prizes awarded each year. The prizes for achievement in science, literature and peace were first awarded in 1901 in accordance with the will of dynamite inventor and businessman Alfred Nobel. An economics prize was established in 1968.
The Nobel laureate for physics will be announced on Tuesday, followed by the chemistry Nobel on Wednesday, literature on Thursday and the Nobel Peace Prize on Friday in Oslo.