After a day of news saturated with images of smoking plane wreckage and reports that perhaps dozens of his fellow HIV researchers heading to the 2014 AIDS conference in Melbourne may have been on board Flight MH17, Richard Elion had to board a long flight from Los Angeles to Australia.

“I am about to leave for Melbourne,” Elion, an HIV specialist and clinical research director at Whitman-Walker Clinic in Washington, wrote from his iPhone Thursday night on his way to the airport in Los Angeles.

“It is hard to get excited about sharing information yet without a time to mourn,” he wrote. “It is very sad and will cast a pallor over the meetings.”

On the ground in Melbourne on Thursday afternoon, organizations scheduled to attend pre-conference events held emergency meetings to plan the painful process of contacting families of colleagues and staff they feared may have been on board the flight shot down in Ukraine. Missing, among others, was a World Health Organization spokesman, Glenn Thomas, who was on the flight.

Organizers of the conference, which is expecting about 14,000 delegates, had not yet confirmed numbers but were expecting a number of attendees to be among the dead.

The crash claimed the lives of 298 passengers, with no survivors. Every confirmation of a colleague, friend or loved one onboard came with the heavy knowledge of what it meant.

Chris Beyrer, who will take over the presidency of the International AIDS Society at the end of the global conference next week, had just come out of a meeting about losses on his staff when he took a call from The Washington Post.

“I thought you might be one of our folks,” he said when he answered the phone at around 1:00 p.m. Australian time. “We’re awaiting confirmation and names, for their families to be contacted.”

Then there was a long pause and a sharp inhaling of breath as he received word from a Post reporter that the employer of one of his colleagues, a friend of 20 years, had confirmed the colleague was on board.

“I was just with him in Amsterdam a few weeks ago,” he said, speaking of Joep Lange, a preeminent Dutch HIV researcher, former president of the International AIDS Society and father of five daughters, who was one of the first to be named among the passengers of MH17, along with his partner.

“He was a visionary,” said Beyrer, reminiscing about the first time he met Lange as a young epidemiologist working in Chiang Mai, Thailand, in 1993. “I’ll never forget it … my secretary said in Thai some foreigners are here to see you. They want to talk to you about HIV. So I said, ‘All right,’ and in walked Joep.”

Elion, who also greatly admired Lange, described him as a great physician who “merged science with a social purpose and a sense of justice. He is not a person who cannot be replaced, rather remembered with bittersweetness.”

As Lange held the presidency Beyrer will soon take on, he said he could only hope to emulate his predecessor, who he knew as not only a “tremendous leader in the scientific and clinical study of AIDS,” but also as an “engaged advocate” who “played an instrumental role in convincing many skeptics it would be possible to deliver HIV treatment to the poorest countries in the world.”

“We’re still not even half way there — there are still half of those infected not living with treatment and resources are declining. That same combination of advocacy and science is needed to finish this fight,” Beyrer added, noting that this year’s conference, which will take place from July 20 to July 25, will focus on the need to provide access for key populations at risk.

Death in the line of duty is not new to this group. Many have worked and traveled in poor nations with infrastructures that make trips inherently hazardous. Some have died in car accidents in such places.

“It always hits home that this is a part of our work,” said Beyrer. “Those of us out working on this pandemic always feel it.”

The AIDS research community has lost important leaders in the field before to aviation tragedies — Irving Sigal, a molecular biologist who helped develop the drugs used to treat HIV, died when Pan Am Flight 103 exploded over Lockerbie, Scotland, in 1988. Ten years later, prominent researchers Jonathan Mann and Mary Lou Clements-Mann died when Swissair Flight 111 crashed off the coast of Nova Scotia.

“What if the cure for AIDS was on that plane?” asked Canadian HIV researcher Trevor Stratton, who had arrived early to Sydney, according to the Australian Broadcasting Corporation.

While reports are circulating that more than one-third of the 298 passengers on the flight were medical researchers and advocates attending the conference — and organizations are saying that they are aware more of their colleagues and staff are suspected to have been on board — only a few names have been confirmed so far.

As well as Lange, World Health Organization media adviser Glenn Thomas was confirmed as one of the six Britons on the plane by one of his colleagues at WHO, Rachel Baggaley.

“I’m just devastated. He’s a very close colleague whom I work with on a daily basis. He just had his birthday, he was going to plan all sorts of celebrations,” Baggaley, of the WHO’s HIV department, told Vox.

The 32-year-old activist Pim de Kuijer, whose last photo and post on Facebook was from Schiphol Airport where flight MH17 took off, was remembered by his colleague Nabeela Shabbir of Stop AIDS Now in a tribute published in the Guardian on Thursday.

Shabbir said Kuijer’s final journey, en route to the AIDS conference, “typified his concern for others.”

Australian Foreign Minister Julie Bishop said “a number of passengers” were traveling to the conference, set to begin on Sunday. She noted that  some of the world’s foremost researchers were thought to have been on the flight.

A moment of silence was held in the Australian House of Representatives to honor the dead, AP reported, which included 27 Australians. Speaker Bronwyn Bishop, who is scheduled to address the AIDS conference on Monday, said she knew there will be “many empty spots.”