The new strain of the mpox virus is spreading quickly along the eastern border of the Democratic Republic of Congo and is “the most dangerous yet”, says the World Health Organization. The current outbreak has been driven by sexual transmission but there is evidence this strain can also be passed on through close skin-to-skin contact. Those now being infected include schoolchildren, healthcare workers and entire households.
Meanwhile, in South Africa, an outbreak has killed three people so far. Border authorities are screening travellers into and out of the country.
Virologist Cheryl Walter explains the history of mpox, the symptoms and why we should be worried about virulent virus mutations.
What are the symptoms?
Symptoms of mpox start off being quite vague – fatigue, aches, fever, headache, respiratory symptoms and a rash.
The rash symptom is a useful differentiator from other common viral illnesses. With mpox, the rash can be itchy and painful and quickly develops into fluid-filled blisters that then scab over.
The fluid in these blisters is infectious and mpox can be spread by sharing towels or toothbrushes, for example. Some people have only a few blisters and they might be hard to see, depending on where they are on the body. And some people have no symptoms.
While treatment for mpox is mainly supportive (such as rest, hydration and pain relief), people who are hospitalised with severe mpox can be treated with broad spectrum antivirals and monitored more closely.
What’s worrying about recent outbreaks?
By genetically analysing old samples from mpox patients, we now know the mpox outbreak started gathering momentum in Nigeria around 2016. More and more people contracted mpox, the outbreak spilled over into other African countries, spread outside Africa and has since been detected in 116 countries.
In July 2022, the WHO declared mpox a public health emergency of international concern. At the time of writing this, a total of 97,745 people had been infected and 203 people had died since the start of the outbreak, with most cases confirmed as the less severe clade II variants.
A couple of worrying observations and discoveries have since been made about this surge in mpox cases.
Firstly, mpox is now readily spreading from person to person although scientists are not entirely sure why.
Secondly, because of this sustained transmission, it is also mutating faster and two sub-clades (side branches) called clade Ib and IIb have been discovered.
Thirdly, there is no licensed, mpox-specific vaccine to prevent infection, nor are there specific antiviral drugs available to treat clinically vulnerable people who can get very ill and die with the virus.
What is mpox?
Mpox, previously called monkeypox, is a pox virus that was first identified in Denmark in laboratory monkeys that had been exported from Africa in the 1950s. Initially, it was probably presumed to be a pox virus that just infected monkeys, but the first human cases were documented in the Democratic Republic of Congo in the 1970s. Cases were caused by small animals, such as monkeys and small rodents, transmitting the disease to humans – and so the name stuck. This virus didn’t get a lot of attention until recently.
The name has been changed to tackle any stigma associated with it, but also to emphasise how this virus has changed in 50 years of confirmed human cases.
Mpox is related to other pox viruses, including cowpox and, importantly, the now eradicated smallpox. It is not related to the very common chickenpox virus, although many of the symptoms of infection are the same.
Genetically, mpox viruses cluster into two main branches that are called clade I and clade II. Clade I virus infections are associated with a high case fatality rate of up to 10%. Clade II, which is found in a much larger geographical distribution spanning western Africa, is associated with a much lower case fatality rate of 1%.
Clade I viruses tend to be found in the Democratic Republic of Congo and are found far less often in samples than clade II. Both are transmitted the same way: close physical contact between humans, including sexual transmission.
While animal to human transmission can occur, the recent healthcare messages have focused on high-risk groups such as sex workers and men who have sex with men, two groups that have been disproportionately affected by the recent outbreak.
Anyone who exhibits symptoms of mpox infection – or who has had close and not necessarily sexual contact with a confirmed case – should be tested.
What next for mpox?
First and foremost, better communication from healthcare agencies is needed on the types of transmission that can happen between people, where they can get tested and how at-risk groups can be better protected. Learning from the HIV/AIDS crisis, more needs to be done to destigmatise mpox and any preconceptions about it.
Secondly, a tailored vaccine is needed to protect against new infections. An mRNA vaccine candidate is already in clinical trials.
Better drugs and treatment regimes need to be developed to protect patients who contract severe mpox.
Lastly, we need to understand why a virus like mpox has come to the fore. One likely reason is that the smallpox vaccine, last routinely used over 40 years ago, also protects against mpox. With more and more of the population unvaccinated against the related smallpox, mpox can now jump from person to person unhindered.
Smallpox, a lethal pox virus that can readily spread from person to person, was eradicated in the early 1980s because of a highly effective vaccination campaign.
That campaign was so effective that we no longer need to vaccinate everyone for smallpox. It also means that contingency stocks of smallpox vaccines are relatively small and it will take time to scale up production.
The transmission of mpox does need to be halted as much as possible. This virus has already shown it can mutate and new variants could potentially be more easily transmitted than the current circulating viruses.
What about other pox viruses?
Surveillance schemes monitoring pox viruses in animal populations and the existing mpox variants are essential in staying ahead of the curve.