The Nobel Prize in Physiology or Medicine was awarded jointly to Dr. Harvey J. Alter, Michael Houghton and Charles M. Rice on Monday for the discovery of the hepatitis C virus, a breakthrough the Nobel committee said had “made possible blood tests and new medicines that have saved millions of lives.”

“For the first time in history, the disease can now be cured, raising hopes of eradicating hepatitis C virus from the world population,” the committee said in a statement. They announced the prize at the Karolinska Institute in Stockholm.

About 71 million people worldwide live with a chronic infection of the hepatitis C virus, a blood-borne pathogen that can cause severe liver inflammation, or hepatitis, and is typically transmitted through shared or reused needles and syringes, infected blood transfusions and sexual practices that lead to blood exposure.

Tests and treatments “all start with being able to recognize the virus exists,” said Craig Cameron, chair of the department of microbiology and immunology at the University of North Carolina at Chapel Hill and a hepatitis C virus researcher.

The discovery of the hepatitis C virus solved a thorny scientific mystery that had plagued physicians and researchers for years.

Credit…National Institutes of Health/Agence France-Presse — Getty Images

A number of hepatitis viruses can infiltrate the liver and cause a range of health problems, some of which are fatal. One of the main ways that hepatitis is transmitted is through blood transfusions, a life saving procedure central to modern medicine that could have deadly consequences when blood was contaminated.

The hepatitis A virus usually has few long-term impacts on the people it infects. Another virus, hepatitis B virus, tends to linger in the body and is responsible for hundreds of millions of chronic infections around the world, many of which remain undiagnosed. The discovery of the hepatitis B virus earned Baruch Blumberg the Nobel Prize in Physiology or Medicine in 1976.

In the 1970s, Dr. Alter led a team of scientists in discovering that most cases of post-transfusion hepatitis couldn’t be linked to Type A or B viruses — a hint to the existence of an pathogen that had not yet been described.

Credit…Richard Siemens/University of Alberta, via Agence France-Presse — Getty Images

In the 1980s, Dr. Houghton, along with two colleagues Qui-Lim Choo and George Kuo, became the first to identify and formally name the hepatitis C virus as the infectious culprit. The work led to the development of a diagnostic test to identify the virus in blood, enabling doctors and researchers for the first time to screen patients and donors.

Angela Rasmussen, a virologist at Columbia who spent her postdoctoral fellowship working on the hepatitis C virus, described the pathogen as “a tricky virus to work with.” She added that Dr. Houghton’s work, which isolated the virus’s genetic sequence, bolstered the case that it was a new pathogen and distinct from the viruses behind hepatitis A and B.

Dr. Alter and Dr. Houghton later shared the Lasker Award for Clinical Medical Research in 2000 for their work.

Dr. Rice’s genetic experiments added important details to scientists’ understanding of the virus, showing that it could be isolated in the lab and cause disease in an animal host, the chimpanzee. These studies nailed the hepatitis C virus as the sole infectious agent responsible for the mysterious “non-A, non-B” cases of hepatitis and set up a crucial animal model for future studies.

“Without Charlie, we still probably would not have completed the story,” Dr. Cameron said.

Credit…John Minchillo/Associated Press

The hepatitis C virus is responsible for tens of millions of long-term infections around the world. Because the infections can spread and persist without symptoms, many don’t know they carry the virus. But once it establishes itself in the body, the pathogen can silently erode the liver’s function over the course of years and decades, later flaring up as severe inflammation or cancer.

If not caught early, a long-term hepatitis infection can be extremely difficult to treat. Many people infected with the hepatitis C virus require liver transplants.

Work by the three awardees paved the path for highly accurate and effective blood tests for the hepatitis C virus. In many parts of the world, screening blood for hepatitis has driven post-transfusion hepatitis rates down to near zero.

Still, most people living with the hepatitis C virus have not received a diagnosis, especially in low-income countries, where testing rates remain below 10 percent.

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Credit…David Degner for The New York Times

Numerous life saving treatments have also been developed for the hepatitis C virus, many of which are in regular use today. When available, hepatitis C antivirals can block the virus from multiplying in the body, and can cure people of the infection in weeks. Researchers around the world, including Dr. Houghton, are now at work on a vaccine that could prevent future hepatitis C virus infections and disease.

“For the longest time, we had nothing to treat this virus with,” said Dr. Guadalupe Garcia Tsao, a cirrhosis expert at Yale University. Preventing the disease, she added, was also nearly impossible without accurate tests. “For most of my career, it was the bane of my existence. But from the moment they made these discoveries, the numbers of sick people went down dramatically.”

Even hepatitis C drugs that originally failed to clear the approval pipeline have found new use in modern times: Remdesivir, one of only a handful of treatments with emergency authorization from the Food and Drug Administration to treat severely sick Covid-19 patients, was originally developed as an antiviral against the hepatitis C virus.

“That’s really the story of investing in basic science, and having it pay off later down the road,” said Stephanie Langel, a virologist and immunologist at Duke University.

Dr. Alter, an American, is a medical researcher for the National Institutes of Health in Maryland. Born in 1935 in New York, he earned a medical degree at the University of Rochester before joining the N.I.H. in 1961.

After treating some of the first “non-A, non-B” hepatitis patients decades ago, Dr. Alter expressed wonder at watching treatment for the illness evolve. Modern drugs can cure more than 95 percent of patients.

“I could never have imagined this, really, not in my lifetime,” he said Monday during a N.I.H. news conference.

With more testing and affordable access to drugs, it would be possible to “eradicate this disease over the next decades, even in the absence of a vaccine,” he said.

Dr. Rice, born in Sacramento in 1952, is a professor at Rockefeller University in New York. From 2001 to 2018, he was the scientific and executive director at the Center for the Study of Hepatitis C. He earned his Ph.D. from Caltech in 1981.

In an interview Monday morning, Dr. Rice described the utter shock he felt at receiving the early morning phone call notifying him of the award.

“I thought it was because a freezer in the lab was warming up, or it was a wrong number,” he said. Even after getting over “being mad at the phone for ringing,” added Dr. Rice, a self-described night owl, “my initial impression was this had to be a crank phone call.”

Dr. Cameron, a frequent collaborator of Dr. Rice’s, described him as welcoming, generous and a dedicated and prolific mentor. “His lab has really populated the flavivirus field,” Dr. Cameron said, referring to the virus family that includes hepatitis C virus. “I was not formally a trainee, but I feel like I was adopted by him early on.”

Dr. Houghton, born in Britain, is a Canada Excellence Research Chair in Virology and the Li Ka Shing professor of virology at the University of Alberta. He is also director of the Li Ka Shing Applied Virology Institute at the university. He earned his Ph.D. from King’s College London in 1977.

Shortly after the award’s announcement, scientists on social media noted that Dr. Houghton in 2013 declined to accept the Canada Gairdner International Award, which he criticized for failing to include his colleagues Dr. Choo and Dr. Kuo. But in a news conference on Monday, Dr. Houghton said he felt it would be “really too presumptuous” to turn down a Nobel, and highlighted the contributions of his colleagues, with whom he is now developing a hepatitis C vaccine.

“Great science is often a group of people,” he said. “Going forward, we somehow need to incorporate that.”

The Nobel science prizes have long been criticized for failing to amplify the achievements of women and people of color in the scientific community.

“While I am always happy to see virologists recognized for their excellent work, the Nobel committee continues its streak of recognizing the achievements of white men,” Dr. Rasmussen said. “I really wish the Nobel committee would consider recognizing equally substantive achievements by women or people of color, and by scientists outside of North America or Europe.”

Dr. Rice also stressed the importance of community and collaboration in his discoveries.

“We’re all a few in a cast of thousands,” he said. “I feel a little bit odd — a combination of humbled and embarrassed. I think there are many people who should feel very good about what they contributed today.”

The prize was awarded to William G. Kaelin Jr., Peter J. Ratcliffe and Gregg L. Semenza for discoveries about how cells sense and adapt to oxygen availability. These cellular mechanisms control, for example, adaptation to high altitudes and how cancer cells manage to hijack oxygen.