In a recent study published in Science, researchers from the University of Edinburgh and other institutions have revealed that monkeypox, now officially called mpox, has been evolving in humans since at least 2016. This new information challenges the previous understanding of the virus as a zoonotic disease, primarily transmitted from animals to humans.

Monkeypox first emerged in the 1950s when an outbreak was observed among lab monkeys imported from Africa to Denmark. In the 1970s, the first human cases were documented, and the virus was identified as a close relative of smallpox, causing rashes and flu-like symptoms.

Prior to 2022, monkeypox was believed to be transmitted only rarely between humans, with zoonotic transmission considered the main source of infection. However, in early 2022, unexpected human-to-human outbreaks occurred globally, with over 90,000 cases reported in 115 countries. These cases were predominantly transmitted through sexual contact among gay and bisexual men. While most of the spreading strains were less lethal, the epidemic still resulted in 157 deaths.

The researchers found that the early epidemic strains in 2022 were genetically related to strains documented in 2018 that originated from Nigeria, a region where zoonotic transmission of monkeypox is endemic. However, the 2022 strains displayed significant genetic differences from their 2018 counterparts. The researchers propose that these differences occurred due to rapid mutations of the virus within humans, allowing it to adapt and spread more easily among people.

Interestingly, these mutations primarily affected how the virus responded to a specific antiviral enzyme called APOBEC3, produced by human cells. This led the researchers to conclude that the virus has been gradually adapting to human hosts for a longer period than previously thought. By leveraging these APOBEC3-related mutations, the study estimates that mpox strains have been circulating between humans since at least 2016.

These findings challenge the existing understanding of monkeypox as a zoonotic disease, highlighting the need for a shift in public health perspectives. The authors stress that sustained human transmission of mpox has been occurring for a significant period, suggesting that the virus's ability to spread between humans is more widespread than initially believed.

While the current epidemic has been largely contained, thanks to vaccination efforts and awareness campaigns, it is essential to maintain vigilance and global surveillance. The study authors emphasize that eliminating mpox from the human population and preventing its reemergence will require a comprehensive, globally coordinated approach.

"It is critical that global public health affords MPXV cases in countries that are historically considered to have endemic reservoir species equal attention and concern to those elsewhere," wrote the authors. "Surveillance needs to be global if MPXV is to be eliminated from the human population and then prevented from reemerging."

As the understanding of mpox continues to evolve, the study's findings shed light on the virus's past and raise important concerns about its future. To effectively combat the disease, sustained efforts and global collaboration will be crucial in the ongoing fight against monkeypox.