At least 28 million people worldwide have died from Aids – their bodies' defence systems ravaged by the HIV virus to the point where everyday infections become life-threatening.

More than 20 years since HIV was first recognised, there remains no vaccine against HIV and no cure for Aids, although a new generation of drugs has dramatically extended the life expectancy of those who contract HIV.

Click through this guide to find out about how HIV attacks and how the drugs fight it.