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What is mpox and why is it spreading?

The virus that causes mpox, formerly known as monkeypox, was first discovered at the end of the 1950s, but there are signs it has undergone changes in the past three to four years that have enabled it to pass between humans more easily.

The first thing everyone should know about monkeypox is that it actually has very little to do with monkeys.

“It was first discovered in monkeys in a laboratory setting in Denmark, it does infect monkeys, and has been isolated from monkeys, but they’re not the primary reservoir for the disease,” says Sagan Friant, an anthropologist at Pennsylvania State University in the United States. “We think of a reservoir as an animal that can transmit the disease but does not suffer or die from it.”

Friant has been studying monkeypox in Nigeria for more than 15 years and was about to begin a new research project just as the Covid-19 pandemic hit. She says it’s likely – but not yet proven – that the monkeypox virus originates in rodents. At the end of 2022, the World Health Organization announced it was renaming the virus as mpox.

“For a long time, scientists thought that diseases in primates were the most threatening to humans because of our close similarity genetically, and that’s true,” she says. “But we’re realising that infectious diseases from rodents and bats are of increasing importance when we’re thinking about spill-over of new diseases into human populations.”

Infections that pass from animals to humans are known as zoonotic diseases. Some of these also have the ability to pass from human to human once they make the jump across species.

In that respect, Mpox has some similarities to Covid-19. But it’s been around a lot longer than the coronavirus behind the recent pandemic.

Where did mpox come from?

Monkeypox was first identified in 1958 at a laboratory in Copenhagen, Demark when it was discovered in monkeys that had been imported from Singapore a couple of months earlier. The first case in humans was not reported until 1970 when a nine-month-old boy admitted to a hospital in the Democratic Republic of Congo was found to have been infected with the virus. Although the young patient lived in an area of tropical rainforest populated by monkeys, doctors were not able to establish if he had recently come into contact with an infected monkey or if it had come from another source. The boy recovered from the infection, but sadly contracted measles a few days later and died.

While it is likely there were human cases before this where the virus was not identified – it causes lesions that are similar to those seen in other pox infections such as smallpox – there have since been cases in a number of African countries before the first outbreak in the US in 2003 when 70 cases were reported. It is thought on that occasion the virus was brought to the US in infected prairie dogs. They had been kept as pets and housed with Gambian pouched rats and dormice that were imported from Ghana. Other cases – usually in people who had recently travelled to African countries – have been seen in the UK, Israel and Singapore.