"In think in Africa, it is only comparable in demographic terms to the slave trade regarding the impact it has had on the population," Piot said. "In southern Africa, HIV prevalence continues to go up, and they're already the world record."

Piot said that the sheer population of Asia, home to most of the world's population, makes it a potential problem because even small gains in overall per capita infections equal huge numbers ¡ª especially in countries like China and India, with over 1 billion people each. More than 5 million people are infected in India alone.

The Asia-Pacific region has 8.3 million people living with the virus, the second-highest after sub-Saharan Africa.

Papua New Guinea, which shares an island north of Australia with Indonesia's easternmost Papua province, has one of the region's worst epidemics in a country plagued by political instability, poverty and rampant sexual violence against women. Piot said it's the only place in the region that resembles an Africa-style epidemic.

Piot said Eastern Europe and Central Asia have become a new front where infections have expanded as people have access to more money and started buying injecting drugs ¡ª instead of just shipping them through ¡ª from countries like Afghanistan.

"Absolute numbers are still low, but when you look at the spread of the disease, we know from experience where that leads," Piot said. "The Middle East is the last part of the world where HIV is not spreading rapidly."