How HIV spread across the West

Story highlights

• A recent study revealed how HIV spread throughout the Western world
• North America provided constant flow of the virus into Europe
• Europe absorbed the infection from multiple regions, including North America

In the 1980s, HIV took the world by surprise.

The infection feigned a role as new and unknown, but had already established itself as a pandemic in other parts of the world, without anyone realizing.

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Though the roots of the virus were soon discovered to lie in Africa, where a range of subtypes exist, one in particular -- subtype B -- was spreading rapidly around the globe, particularly in the West, and just how it spread was largely unknown -- until now.

Scientists at the University of Oxford recently solved part of this mystery by analyzing thousands of genome sequences from viruses isolated in different parts of the world. Their study revealed North America to play an influential role in the pandemic and Europe to have been influenced, with the virus arriving in droves from other regions.

"Europe was absorbing the virus," said Gkikas Magiorkinis, a medical virologist at the University of Oxford who led the study. "North America was actively letting the virus out."

Creating a flow

North America was seen to be spreading the virus much more than importing it by transmitting it out of the continent and into Western Europe on multiple occasions.

"It wasn't just a random transition, or single point of introduction, it was happening constantly," said Magiorkinis. He stressed these are movements of the virus, not migrants. "It's not immigrants causing this, as people going on holiday can get infected."

This continuous flow is, in part, thought to be due to certain countries being more influential than others, such as those in North America. A country is considered influential by having many connections to other parts of the world, as once any virus enters, it can then easily spread.

"It was only when it entered the USA that it became a pandemic," said Magiorkinis.

Internal travel

In contrast, Europe was found to have absorbed constant flows of the virus, from multiple regions of the world, including the United States.

"Within Europe, three countries had higher connections: the U.K., France and Switzerland," said Magiorkinis. These connections saw these countries both releasing and absorbing the virus, but with greater numbers coming in, including from the United States.

"The critical issue is population mixing and the fact people acquire, or spread, viruses associated with travel," said Chris Beyrer, Professor of Public Health and Human Rights at the Johns Hopkins Bloomberg School of Public Health. "There's a long history of blame for the spread of the epidemic...but you have to improve control and treatment."

Multiple studies have shown the benefits of antiretroviral treatment in preventing transmission of HIV as levels of the virus can become undetectable once on treatment.

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After arriving in Europe, the virus soon spread within the continent, but with a clear segregation between Eastern and Western Europe as each side evolved its own pockets of the epidemic. In Western Europe (as well as North America), HIV mainly affects gay communities, causing concentrated epidemics. In the U.K., more than half of new HIV infections occurred among gay men in 2014, despite them making up an estimated two to three percent of the male population. But in Eastern Europe, the virus mainly infects injecting drug users and transmission dynamics are quite different as the virus is not spread sexually.

This segregation of epidemics occurred until the collapse of the Soviet Union in the 1990s when movement -- and transmission --promptly changed.

"When the Soviet Union fell, we can see the virus in that area spilled over into Western Europe, probably due to migration," said Magiorkinis.

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