Why did HIV take so long from the time it jumped species (sometime in the early 1900s) and began circulating among humans to blow up into a global pandemic in the 90s?

Question

Make that 80s.

In: Biology

Answer 1

We don’t really know the first time HIV infected a human. It could have happened many times prior to the beginning of the pandemic, but it simply never spread beyond the initially infected person because of the remoteness of the location, low population density, or we didn’t identify it because the HIV virus was unknown at the time, and the symptoms of AIDS could have easily been missed or confused with other tropical diseases.

The reason it turned into a pandemic when it did is because of rapidly expanding human population in the Congo (where the virus originated) and increased travel. HIV made the definitive jump to humans in the early 20th century. Brazzaville and Kinshasa (then called Léopoldville) were, at the time, rapidly expanding human settlements, but travel was still difficult. This means there were enough people to sustain the slow spread of the virus throughout Africa but had little to no contact with other continents. By the 60’s and 70’s, this had changed, it and increased travel meant infected persons could make their way away around the world and wind up in highly populated cities which were primed for an outbreak. The current theory is that HIV first arrived in the US via the Caribbean sometime in the early 70’s.