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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 . 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.

But since . While this has worried health authorities and scientists, the number of infections in these outbreaks are a fraction of those seen in Africa, where the disease is endemic. A major outbreak in the Democratic Republic of Congo has seen more than . The version of the virus causing the DRC outbreak is a more deadly version, known as clade I, compared to the version that caused , known as clade II.��

The US Centers for Disease Control and Prevention says  and that people who have been fully vaccinated, or have had mpox previously, should be protected against the clade I virus. have yet been reported in the US.

Exactly where the surge in outbreaks since 2022 originated, however, is still something of a medical detective story. Genetic analysis has revealed that the variant of the virus causing the outbreaks belongs to a branch of the mpox evolutionary tree that , but no clear link to any countries where the virus is endemic has been found. Instead, there is now that the virus might have been , if not .

Some genetic analysis – although still preliminary and yet to be peer-reviewed – has indicated that the West African mpox virus (clade II) may have  as early as it could have been . And since then it has accumulated a that have made it better able to infect and pass between human hosts – including one that may help it to .

More recently a new variant of the mpox virus, known as , has appeared in the DRC and appears to spread more easily through close contact. It seems to have first emerged in the , north Kivu, and is particularly . Research suggests the variant could have .

Unlike the virus that causes Covid-19, which primarily spreads through tiny droplets expelled as we breathe and is highly infectious, mpox is not as readily transmissible. It instead relies on close physical contact – usually prolonged – to pass from person to person, or animal to person.

"It could be contact with someone who has an infectious rash, such as lesions, scabs and bodily fluids," says Madeline Barron, from the American Society for Microbiology (ASM). "You can also get it by touching items that someone who's infected may have touched."

A study published in the New England Journal of Medicine found that between April and June 2022, , but it's not clear why this is the case. It could just be coincidence – once a disease is introduced to a community, it tends to spread within that community. And there is no evidence that mpox passes any quicker through a population of men who have sex with men than any other group. Nor is there any evidence that it is more infectious to men than women.

"We don't know if the virus can spread specifically through sexual transmission routes, such as through vaginal secretions or semen, but it seems to be that intimate contact is promoting the spread," says Barron.

Although virus has been by researchers, it does not necessarily mean that this is how it is spreading. The mpox virus is a packet of genetic information encased in an envelope of proteins and a membrane. It requires all these components to be in working order if it is to infect cells, and although viral DNA can be detected in semen, the virus itself may not be viable and capable of infection.

Another important thing you need to know about mpox is that it is deeply unpleasant. Compared to the Central African strain of the mpox virus, the West African version is generally .��The mortality rate of the . For those infected by clade II, 99.9% survive. As of June 2024 there had been 99,176 confirmed cases since the outbreak began in 2022 according to the WHO and .��

But even if the chances of dying are relatively low, patients with monkeypox have reported how painful and debilitating it is.

"It's long, it's nasty and you don't want to get it," says Barron. "People may feel flu-like symptoms in the beginning, with fever, headache, stuff like that, but as the disease progresses you get a multi-stage rash, lesions can develop in your mouth, your feet and genital region and these develop into pus-filled blisters."

It can take between , although typically this incubation period is 6-13 days. Initially it begins with headaches, fever, muscle aches and fatigue for the first few days. One distinguishing feature of the virus is . Eruptions on the skin tend to appear within a couple of days of the fever appearing.

Some three to four weeks after infection, the blisters will eventually scab over and fall off. Scarring, however, is . There is no specific treatment, other than medicines to treat the symptoms, and, like most diseases, your chances of getting seriously ill or dying depend on factors such .

What perhaps makes monkeypox so shocking is that the symptoms look similar to a disease of the past. One that we thought we had seen the back of thanks to a successful global vaccination campaign: smallpox. Monkeypox is from the same group of viruses as smallpox, although a distinct virus. (Read more about .)

Mpox is a brick-shaped virus carrying a double-strand of DNA. This is good news because it means the virus is relatively stable and less likely to mutate into more lethal or more transmissible variants. The Sars-CoV-2 virus that causes Covid-19 contains genetic material made from a single stranded RNA.

"RNA viruses mutate very effectively ­– they're diabolical, in my opinion, they're just really nasty viruses," says Rodney Rohde, a professor at Texas State University with a background in public health and virology. He is the co-author, with Barron, of a 2022 publication for the American Society of Microbiology on the . "DNA viruses typically don't mutate that quickly, even with the , so we don't see mutations having an impact on the severity of the disease."

Part of the reason for this may be because – meaning they don't change any of the viral proteins it needs to infect cells and evade the immune system. Even so, some researchers have in the three or four years . Researchers identified – suggesting separate sources – spreading in the US. there is some evidence that the virus may have been .

�ճ���� in the DRC suggests the virus has been evolving rapidly. It showed a high mutation rate, including some changes in its genetic code that could have helped the virus spread more easily from human to human.�� 

Preliminary unpublished research has also identified potential mutations that have yet to be seen in the virus but could if they were to occur in the future. But this work, if shown to be correct, could also help health officials and scientists look out for signs mpox is evolving into something more worrisome.

The WHO briefly declared mpox to be a in July 2022 but it was then declared over by May 2023 due to progress in tackling the disease. However, the risk posed by mpox has grown, and in August 2024, the Africa CDC declared a due to the rapid spread of new variants of the virus. On 14 August 2024, the WHO declared the surge in mpox cases in Africa . It rasied particular concern about the number of cases in the DRC, where the 15,600 cases and 537 deaths have already exceeded the number for the entire year of 2023.

Among the reasons for the concern lie in mpox's relationship to smallpox.

For almost 200 years, we had been . Today, thanks to a global scientific effort, , and the world was . Although the smallpox virus still exists in secure laboratories, it is no longer a transmissible disease. But neither do we now have any natural immunity to smallpox or similar viruses. And with the in the mid-1980s, so too has the protection it offered against other pox viruses waned.

"We probably had a pretty strong herd immunity across the globe when we eradicated smallpox," says Rohde. "There's some research that shows that if you go back and look at the population in Nigeria, for example, they probably would have spread monkeypox more efficiently had they not been vaccinated against smallpox.

"Once we stopped smallpox vaccinations, we had waning antibodies – my parents, for example, may have some immunity, but it's probably really poor."

The good news is that – . And, even though there have been recent moves to around the world, countries have been replenishing their . Mostly, however, this has occurred in wealthy nations. And that's perhaps the most dispiriting aspect of this most recent monkeypox outbreak. We have known about the disease for more than 50 years but only when it spread to North America and Europe did governments outside Africa appear to take any notice.��

Data from the Africa Centres for Disease Control and Prevention shows that, since the beginning of 2022, there have been some .

"Many of us have been screaming about these types of issues for decades," says Rohde. "In my opinion we don't always think about these things when they're not on our shores."

"Those regions where it is endemic, and it's been a prolonged issue, are still at the short end of the stick in terms of getting the resources, the diagnostics, the vaccines, everything needed to handle the outbreak," adds Barron. "If Covid has taught us anything it's that the world is small and you need a coordinated effort to respond to diseases because diseases don't know boundaries."

A 2020 United Nations report warned of the , exacerbated by our encroachment on natural habitats and the effects of climate change. The bottom line for Friant, who specialises in the health consequences of the interaction between humans and animals, is that we need better monitoring of all potential zoonotic diseases.

"We need more investment in understanding the diseases and preventing that initial spill-over event from animals to humans from happening," she says. "We also need collaboration and capacity building in countries so that they're equipped to respond to these events – it definitely shouldn't just be about protecting the Western world."

Like Covid-19, mpox is just the latest disease to spread from animals into the human population. Given its relatively slow spread and the fact that vaccines are available to prevent infection, it's likely mpox outbreaks can be contained. But monkeypox won't be the last disease of this nature. And the world will need to be ready and vigilant for the next.

* This article was originally published on 2 August 2022. It was updated on 20 May 2024 and again on 13 August 2024 to include details of outbreaks in DRC and some of the latest research on the virus evolution.

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