Baruch S. Blumberg, a Nobel Prize-winning scientist who discovered the hepatitis B virus and subsequently developed a preventive vaccine that saved millions of lives, died April 5. He was 85.

A Philadelphia resident, he died of an apparent heart attack while attending a conference at NASA’s Ames Research Center at Moffett Field near San Francisco, according to a statement posted on NASA’s Web site.

Dr. Blumberg had spent the latter part of his career helping NASA inaugurate its formal search for extraterrestrial life and clues about the origin of life on Earth. For Dr. Blumberg, who was trained a biochemist but became a leading scientist in the fields of virology, oncology and epidemiology, this new field was the next step in a long career of enviable breadth.

“Are we alone? How did life originate? What is life? And what is the future of human beings in space? Some of these are the questions people have been asking forever,” he told the New York Times in 2002. “Just in the last few decades we have the real possibility of answering them.”

He was best known for his work a half-century ago on hepatitis B, a virus that attacks the liver and can cause cirrhosis, cancer and death.

Dr. Blumberg did not set out to conquer the virus. He was interested, instead, in figuring out why some people are more vulnerable to getting sick than others. That simple question led him to farflung villages in Africa and the Arctic — and serendipitously to the discovery of hepatitis B in the mid-1960s.

His identification of the virus allowed for the near-immediate development of tests used to screen potential blood donors, greatly and immediately reducing the transmission of hepatitis B via blood transfusions.

In the 1970s, Dr. Blumberg and a colleague, Irving Millman, developed a hepatitis B vaccine. Since it became commercially available in 1982, more than 1 billion doses have been administered around the world. The chronic infection rate among children has plunged — from 15 percent in Taiwan and more than 10 percent in China, for example, to less than 1 percent in each country.

“I think it’s fair to say that Barry prevented more cancer deaths than any person who’s ever lived,” said Jonathan Chernoff, scientific director at the Fox Chase Cancer Center in Philadelphia, where Dr. Blumberg spent most of his professional life.

For “discoveries concerning new mechanisms for the origin and dissemination of infectious diseases,” Dr. Blumberg shared the 1976 Nobel Prize for Medicine with D. Carleton Gajdusek, who did groundbreaking research on kuru, an incurable and infectious degenerative neurological disorder.

Dr. Blumberg began his hepatitis work at the National Institutes of Health in Bethesda during the 1950s. He joined Fox Chase in 1964 and served as associate director for clinical research and vice president for population oncology before holding the title of distinguished scientist in 1989.

From 1999 to 2002, he served as the first director of the NASA Astrobiology Institute at Ames, lending his formidable intellectual reputation to what had previously been considered fringe science.

The Astrobiology Institute has sent teams of scientists to look for life in some of the most extreme places on Earth: polar ice caps, deep-ocean fissures and boiling geysers. The organisms that can survive in such extreme environments, he said, may offer insights into early life on Earth.

“I’d be very surprised if we found something in space that would look like E.T.,” he told the Times. “If we find something more like a virus or a bacteria, that would be astounding enough.”

Baruch Samuel Blumberg was born July 28, 1925, in New York. The son of a lawyer, he grew up attending Hebrew parochial school.

During World War II, the Navy sent him to study physics at Union College in Schenectady, N.Y. He graduated in 1946 and received a medical degree from Columbia University in 1951.

While in medical school, he spent several months at a hospital in the jungle of Suriname, a country in northern South America. It was there, delivering babies and treating patients in isolated villages where people suffered from mosquito-born diseases and poor sanitation, that he became interested in studying infectious diseases.

“Nature operates in bold and dramatic manner in the tropics,” he wrote in a short autobiography for the Nobel committee. “Biological effects are profound and tragic.”

He married Jane Liebesman, an artist, in 1954. Besides his wife, survivors include four children, Anne, George, Jane and Noah, and nine grandchildren.

After earning a doctorate in biochemistry from Oxford University’s Balliol College in 1957, Dr. Blumberg became chief of geographic medicine and genetics at the NIH. There, he began screening thousands of blood samples to understand the variable disease resistance of different ethnic groups.

Working without the tools of modern genetics, he isolated a protein from the blood from an Australian aborigine. He called the protein the “Australain antigen” and three years later discovered that it was part of the hepatitis B virus.

He detailed his discovery in a 2002 book, “Hepatitis B: The Hunt for a Killer Virus.”

Fascinated by people and cultures, Dr. Blumberg taught medical anthropology at the University of Pennsylvania for many years.

He had been president of the American Philosophical Society since 2005 and was known to pepper his scientific talks with quotes from writers and philosophers such as Thomas Kuhn.

He also enjoyed canoeing, running and playing squash, and he co-owned Antietam Meadows, a cattle farm in Western Maryland. “Shoveling manure for a day on my farm,” he said, “is an excellent counterbalance to intellectual work.”