By Ania Lichtarowicz
BBC health reporter, Rio de Janeiro
Countries in Central Asia and parts of eastern Europe are facing an explosion of Aids/HIV, according to scientists at a conference in Rio de Janeiro.
Scientists say HIV follows the heroin traffic route from Afghanistan
New data shows that the next wave of the epidemic is being fuelled by heroin exports from Afghanistan.
The virus is continuing to spread to areas where the number of cases has previously been low.
Tajikistan, Uzbekistan, Iran, Belarus, Ukraine and Moldova are some of the countries facing the next epidemic.
Scientists at the International Aids Society conference say HIV is following the route of heroin traffic from Afghanistan, through Central Asia and the former Soviet Union, into Eastern Europe.
Young men are most likely to inject heroin. As they are highly active sexually, they could quickly spread the virus into the general population, scientists say.
They explosion of HIV cases is almost inevitable, because prevention schemes like safe needle exchange programmes and drug substitution projects are almost non-existent in the region.
Only 10% of drug users have access.
Scientists have argued that such measures must become commonplace. But tried and tested prevention methods are illegal in some of these countries.
Researchers say that only the implementation of widespread prevention schemes will avert the spread of the virus - and that will require a significant change in the attitude of the governments concerned.