SYDNEY (AP) -- Researchers and activists heading to an AIDS conference in Australia were on the Malaysian jetliner shot down over Ukraine, news that sparked an outpouring of grief across the scientific community.
Among the passengers were former president of the International AIDS Society Joep Lange, a well-known researcher from the Netherlands, and World Health Organization spokesman Glenn Thomas, based in Geneva.
Malaysia Airlines Flight 17, heading from Amsterdam to Kuala Lumpur, Malaysia, crashed Thursday with 298 people on board. American intelligence authorities believe a surface-to-air missile brought down the aircraft, but it was not yet clear who fired it.
A precise number of passengers who were bound for the conference could not immediately be determined. The 20th International AIDS conference starts Sunday in the Victoria state capital of Melbourne.
The Academic Medical Center hospital in Amsterdam said in a statement that two of its staff, Lange and his colleague Jacqueline van Tongeren, were believed to have perished.
"Joep was a man who knew no barriers," the hospital said. "He was a great inspiration for everybody who wanted to do something about the AIDS tragedy in Africa and Asia."
Van Tongeren was head of communications at Amsterdam Institute for Global Health and Development and had previously been an HIV-AIDS nurse, a University of Amsterdam statement said.
Chris Beyrer, president-elect of the International AIDS Society, said if reports of Lange's death were true, "then the HIV/AIDS movement has truly lost a giant."
Nobel laureate Dr. Francoise Barre-Sinoussi, co-discoverer of the AIDS virus and president of the International AIDS Society, paid tribute to Lange in a speech in the Australian capital, Canberra.
"Joep was a wonderful person - a great professional ... but more than that, a wonderful human being," she said. "If it is confirmed, it will be a terrible loss for all of us. I have no words, really, to try to express my sadness. I feel totally devastated."
She later told reporters the conference would continue out of respect for the lives lost: "Because we know that it's really what they would like us to do."
Lange had been working on HIV since the earliest years of the epidemic, participating in clinical trials and research across the world, Barre-Sinoussi said. He had dedicated his life, she said, to "the benefit of mankind."
Sharon Lewin, co-chair of the conference, called Lange a true renaissance man, who also had a keen interest in arts and literature.
"He was passionate about his job and passionate about global health and improving people's lives in low-income countries," Lewin said. "He was quite visionary actually, I think since the very early days of the epidemic and could see what the challenges were that lay ahead."
WHO spokesman Glenn Thomas, who was en route to the conference, was also among the dead, said Christian Lindmeier, spokesman for WHO's Western Pacific region. "Everybody's devastated," Lindmeier said. "It's a real blow."
The International AIDS Society expressed its grief over the news that several of its colleagues and friends were on board.
"At this incredibly sad and sensitive time the IAS stands with our international family and sends condolences to the loved ones of those who have been lost to this tragedy," the group's statement said.
Robin Weiss, an emeritus professor at University College London, said Lange's death was comparable to that of Jonathan Mann, who led WHO's first AIDS department - and who was killed after his flight to Geneva was sabotaged 17 years ago. Weiss noted the AIDS community has grown much larger since then, lessening the impact of any one person's death.
"It's now a much bigger pond," he said. Weiss said that while identities were still being awaited for the other passengers bound for the Melbourne conference, the AIDS community was likely robust enough to bounce back. "It sounds callous but if any of us (working on HIV) are in a plane crash or have a heart attack, it's a loss for the people who know us," he said. "It's a moment of great sadness, but I don't think (Lange's) loss alone sets us back in the fight against AIDS. The momentum to continue is still there."
Dr. Jennifer Cohn of Doctors Without Borders said the AIDS community would honor the loss of their fellow researchers by "re-doubling (their) commitment and efforts to address the HIV pandemic," in a statement.
Former U.S. President Bill Clinton will deliver an address at the AIDS conference, which brings together thousands of scientists and activists to discuss the latest developments in HIV and AIDS research.
Flags at government buildings across Victoria will remain at half-staff throughout the conference, the state premier said.
House of Representatives Speaker Bronwyn Bishop, who addresses the conference Monday, called for a moment of silence in parliament.
"I know there will be many empty spots" at the conference, Bishop said. "And I think that what we're doing is mourning with all of the world and all that had been lost. And we want to see justice but in a measured way."