How did it spread?

People sometimes say that HIV started in the 1980s in the US, but in fact this was just when people first became aware of HIV and it was officially recognized as a new health condition.

According to the research published in Nature, the strain of HIV responsible for almost all AIDS cases in the US was carried from Haiti to New York City around 1971. From New York, it spread to San Francisco around 1976.

Then how did it transmit to Haiti?

The first transmission of SIV to HIV in humans took place in around 1920 in Kinshasa. The area around Kinshasa was full of transport links, such as roads, railways and rivers. The area also had a growing sex trade around the time HIV began to spread. The virus spread along these transport routes via migration and sex trade.

By 1937, it had reached Brazzaville, about 120km west of Kinshasa.

In the 1960s, HIV spread from Africa to Haiti and the Caribbean when many Haitian professionals working in the colonial Democratic Republic of Congo returned home.

Then the virus made its way to the US, from where it spread across the rest of the globe through international travel.