LONDON  -  In 1984, doctors announced they had discovered the cause of the mysterious disease afflicting young, healthy gay men – the Human Immunodeficiency Virus (HIV).

Since then, experts have worked to trace where the virus came from – and now believe they’ve pinpointed when and where the outbreak began, Futurism reports.

HIV began to spread in Kinshasa, the capital of what is known as the Democratic Republic of Congo today, in the 1920s, experts now believe, based on analysis of archived virus samples.

Then known as Leopoldville, capital of the Belgian Congo, it was a rapidly growing metropolis – and its roaring sex trade provided ideal conditions for the virus to spread.

New railways saw up to a million people travelling through the city each year – meaning that the virus could spread into neighbouring areas.

Researcher Nuno Faria built a ‘family tree’ of HIV by analysing HIV genomes from 800 infected people in central Africa.

They compared genome sequences and found that the HIV genomes shared a common ancestor which existed less than 100 years ago.

The researchers pinpointed its origin to 1920, and the Belgian colony’s capital.