Where does monkeypox come from?

The monkeypox virus was first identified in the late 1950s, when it was isolated from monkeys; hence the name. Which is actually a misnomer, because the virus is actually an infection of small rodents and only accidentally jumps into bigger animals when the  opportunity presents. In the decades since its discovery, small numbers of human cases and outbreaks have been documented periodically, most of them within the two parts of Africa where the two main forms - or clades - of the virus are centred. The disease had previously never circulated outside the African continent, and only sporadic cases were picked up internationally in travellers returning from endemic areas. But two years ago, things changed with a massive outbreak that ultimately affected tens of thousands of people across tens of countries. That outbreak, which circulated chiefly among gay men and has since been reined in, was caused by the west African - or clade 2 - form of the virus and marked the first time the agent had spread significantly in communities outside of Africa. Now, since late 2023, another major outbreak has erupted, this time centred on the Democratic Republic of the Congo and caused by the allegedly more aggressive central African - or clade 1 - form of the virus. So far it’s affected thousands of people, including children, and claimed hundreds of lives. Its means of spread, and possibly its infectivity, may therefore be different. It’s already spread to neighbouring Africa countries and could travel farther, prompting the WHO to declare a public health emergency of international concern.

We’ll hear more in a minute about the situation in the DRC - and the international response. But first, what does monkeypox look like when we catch it? I went to Addenbrooke’s hospital in Cambridge to meet Cambridge University’s Mike Weekes, professor of viral immunology and a consultant in infectious diseases…

Mike - A patient with monkeypox would typically be somewhat unwell. They'd have a fever, they'd have a sore throat, a typical rash, which is a telltale sign of monkeypox and they might also have muscle aches, back ache, glands up in the neck.

Chris - How quickly do those features come on after a person is exposed to someone who's effectively given it to them?

Mike - The typical incubation period, if you'd like, is between 5 and 13 days, most often between about 7 to 10 days.

Chris - And how long do those symptoms last?

Mike - Overall, the symptoms can last 2-4 weeks. The longest thing to last is the rash because that goes through a number of stages. It starts as a macule, that flat red spot, becomes a papule, a raised red spot, and then what we call a pseudo pustule, which you'll have seen pictures of on the news, which are raised spots that look like they're filled with pus but are actually solid.

Chris - People who catch it, where do they get it from? How do they pick it up?

Mike - There's a number of routes. The original virus that we saw spreading around the world in 2022, which we call Clade 2b, was predominantly transmitted by sexual contact. The most recent Clade 1b rash that has started in the Democratic Republic of Congo seems to be transmitted not only sexually but by lots of different forms of close contact. The most risky exposure is the exposure to the rash itself and this is the biggest way for the virus to be transmitted, by contact with the rash, and particularly after you've come into contact with a rash touching your mouth or your eyes or any of your mucus membranes, but it can also be transmitted by the bits of the rash that have fallen off. So if you have contact with linen or clothes, or even if you accidentally prick yourself with a needle that's been exposed.

Chris - That means then there are lots of ways that a healthcare setting has to be cautious when they're dealing with possible cases of this to make sure that it doesn't spread to other patients or to staff. Walk me through how an average hospital who might see a case of this would handle it to minimise those sorts of risks.

Mike - You're quite right. So mpox Clade 1b is classed as a high consequence infectious disease, and that means that it can relatively easily be spread within a hospital or within a community, and also it may have an appreciable mortality rate. Other examples of high consequence infectious diseases are things like Ebola, certain strains of flu and MERS. The first thing to do is to isolate the patient somewhere safe, and so what you would typically do would be to put them in a negative pressure room, and that means air goes into the room because the air pressure in the room is lower than the air pressure outside, and then when it exits, it goes through a series of very powerful filters to get rid of any viruses. The other thing that we have to do is have adequate PPE, and for a high consequence infectious disease the principle is to cover up all exposed skin and to filter the air. What you have to do is wear a hood, an FFP3 mask, gowns to cover your whole body, boots, and at least two pairs of gloves.

Chris - And are doctors who do the sorts of job you do, are they prepared for that? Is the UK's level of preparedness quite good? Obviously we've had a bit of a trial run with this because two years ago we saw this initial rash of cases, which was the Clade 2b, now we've got this slightly different form, but it presumably has given us some grounding in how best to tackle this?

Mike - Both from the Coronavirus pandemic and the Clade 2b mpox outbreak, we've had a lot of preparedness and so we know very much what we should do, exactly how we should wear PPE, and exactly how we should treat patients like this. We have a network around the country of hospitals prepared to deal with high consequence infectious diseases.

Chris - What about dealing with people who might have come into contact with a case but haven't yet got it? Is there anything we can do for them? Or how do we handle those sorts of contacts?

Mike - So if it was a very significant contact then the main thing would be to isolate the patient and to warn them of symptoms they might expect, but that's pretty much it. Basically, you are not infectious until you develop symptoms. There've been a very few cases of infection being transmitted before the development of symptoms. This mpox is really not the same as coronavirus where you became most infectious before you develop symptoms. Now, you are infectious when you develop symptoms and particularly when you develop a rash. You know you have it. It's not really transmitted without symptoms.