Participants at a world Aids conference in Mexico are calling on Iran to release from detention two doctors known for their pioneering work on HIV/AIDS.

Human rights groups have claimed the two brothers, Arash and Kamiar Alaei, have been imprisoned.

Aids has long been a taboo topic in Iran, where the stigma of the virus makes it difficult for people to seek treatment.

But as Ali Reza Ronaghi reports things are starting to change.