Mubashar Sheikh, executive director of the Global Health Workforce Alliance, an umbrella group hosted by the World Health Organisation (WHO), said around four million healthcare workers were urgently needed.
Lack of trained staff was hampering the rollout of antiretroviral drugs in poor countries, threatening the UN and Group of Eight (G8) targets of universal access to this lifeline by 2010, he told AFP in an interview on Tuesday.
The shortage also endangered two of UN's Millennium Development Goals (MDGs) -- halting and starting to reverse the spread of HIV and malaria, and improving maternal and reproductive health by 2015.
Fifty-seven countries "are in crisis" in terms of worker shortages, Sheikh said, speaking on the sidelines of the 17th International AIDS Conference in Mexico City.
"Our message is that you have to address this issue of healthcare workers," Sheikh said.
"You cannot wait until 2015 to work on the shortage of health workers. If you're interested in the MDGs, fill this gap now, in the next to three years, only then do we have some hope of achieving these targets.
"Otherwise, you can forget these goals, it's simply not possible."
Around three million badly infected people in poor countries have access to the antiretroviral drugs that suppress HIV but do not eradicate it. This is less than a third of the total in need.
Administering the drugs in poor countries is labour-intensive due to the lack of sophisticated laboratories and diagnostics available in rich countries.
Community caregivers are being enrolled as the first step in treatment process, advising people with HIV about the need to take their medications each day and warning of the possible side effects. Nurses often take on the role doctors have in rich countries, monitoring the patient's response to these powerful drugs.
"There is a clear correlation between the pace of antiretroviral rollout and the shortage of health workers," said Sheikh. "It is having an extremely adverse effect."
He said one of the biggest problems was the recruiting of staff by rich countries, which drained skilled workers from poor economies.
"In Zimbabwe, 50 percent of nurses are leaving," he said.
Sheikh said he was encouraged by commitments by the Global Fund to Fight AIDS, Tuberculosis and Malaria to allot funds for supporting the recruitment of health workers.
And he praised the United States for its plans to "recruit, train and retain" 150,000 health personnel in poor countries over the next five years.
Next year, the WHO's World Health Assembly is expected to approve a non-binding code of practice under which wealthy countries that recruit for personnel in poorer countries also promise to invest in training in those economies.
"We have recently seen policy changes, and the message coming out is positive. It is encouraging," he said.