Oxford Sparks

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Emily Elias: A deadly outbreak of hantavirus on a cruise ship has made waves around the world. On this episode of the Oxford Sparks Big Questions podcast, we’re asking: should I be freaked out by the hantavirus?

Hello, I’m Emily Elias, and this is the show where we seek out the brightest minds at the University of Oxford, and we ask them the big questions. And for this one, we found a researcher who wants to help separate fact from fiction.

Daniel Wright: I am Daniel Wright, and I work as a senior postdoctoral researcher in the Outbreak Pathogens Team in the Oxford Vaccine Group. It’s part of Professor Teresa Lamb’s team, and we design and develop vaccines against outbreak pathogens – the sorts of pathogens which can cause explosive outbreaks and large epidemics and pandemics. More specifically, it’s viruses which cause haemorrhagic fevers, so a sort of internal bleeding. They have quite high case fatality.

Emily: Really lovely stuff then.

Daniel: Yeah. Nice stuff.

Emily: Um, okay. So we’re talking today because obviously there are a lot of headlines right now about hantavirus, and we’re going to come to you as our guide to help us understand this thing. So maybe we should start with, like, what is it?

Daniel: Yeah. So hantavirus is actually a family of viruses. It’s not a single virus.

Very broadly, they’re split into hantaviruses which cause disease in Europe and Asia, and then there’s another set that cause disease in the Americas, North and South America.

They’re spread by rodents, so the vast majority of hantavirus cases are people being directly infected from an infected rodent. That’s typically from things like droppings or urine or any other sort of bodily fluids that can be dried and kicked up and then breathed in. That’s how most people will get a hantavirus infection.

The hantavirus infection that’s causing an outbreak currently on the cruise ship is called Andes virus. It’s one of these hantaviruses and, again, it’s typically spread by contact with rodents. But this is one of the hantaviruses which can also spread person to person. That’s why there’s a little more concern around this type of hantavirus outbreak than there might be with others.

Emily: Okay. And what kind of symptoms are people getting if they catch it?

Daniel: It starts off with typical kind of flu-like symptoms – headache, chills, fever, body aches – and then it can progress into a much more severe form. That’s different depending on whether it’s the type of hantavirus which occurs in Europe and Asia or the one that occurs in North and South America.

The severe form of the hantaviruses which cause disease in Europe and Asia can cause haemorrhagic fever, so kind of internal bleeding and kidney problems. That’s the kind of severe form. The hantaviruses in South America cause a respiratory problem in the severe form. So those are the two severe forms of hantavirus infection.

Emily: And how often do we see these types of infections, whether it be the European one or the South American one?

Daniel: They occur pretty sporadically, but there’s quite a few of them. So what’s called the Old World hantaviruses, those that affect Europe and Asia, there are potentially 100,000 cases a year. They have relatively lower case fatality than the ones in South America.

The virus causing an outbreak on the ship currently is Andes virus, as I mentioned. There have been a number of cases over the last 30-odd years. It was initially identified, the severe form, in the 1990s, and since then there have perhaps tens of cases every year. So there’s nothing about this outbreak which is particularly different, except it’s occurring on a cruise ship, which, as far as I know, is new.

But there’s nothing to suggest that the virus is behaving differently to how it usually does, or it’s more transmissible or it’s more severe. It’s very much as we expect from this virus.

Emily: And nothing about it being human to human strikes you as, like, “Oh, well, that’s unusual”?

Daniel: So it’s certainly unusual among hantaviruses, but it’s already known that this Andes virus can cause human-to-human transmission. That absolutely is one of the main concerns because that obviously is one of the barriers for a disease to cause real problems amongst humans, if it can sufficiently or efficiently spread person to person. So that is, I think, unique amongst hantaviruses, but it has been shown previously with this virus in previous outbreaks.

Emily: And how is it spread human to human? Is it, like, breathing on you? Is it swapping spit, fluids? What are we doing here?

Daniel: First, there’s a lot we don’t know about hantavirus transmission. What we do know is that when we look at all the previous outbreaks that have occurred with this virus, some of them don’t seem to involve any human-to-human transmission. It’s just directly from a rodent to a human, and then it kind of peters out.

But the ones that have been human to human, what happens is, where this occurs, typically in rural regions of Argentina and Chile, there are public health measures in place for those countries. It’s like we were experienced with Covid, where there’s contact tracing and quarantining.

Based on all of those previous outbreaks, looking at all of the contacts, what’s clear is that the majority of the time, the people who are becoming infected are only those with significant, sustained contact with an infected individual. And less, as like it was for Covid, where essentially it replicates very efficiently in the throat and the nose and the upper airways, so a simple breath or a sneeze or a cough is enough to transmit a lot of virus. That seems to be unlike how Andes virus transmits. It’s a lot less efficient going from person to person. We know that it seems to require this sustained contact because it’s those people who seem to be getting infected from initial index cases, as opposed to everyone that had a passing moment with someone who was infected.

Emily: Is there a vaccine for it? I mean, you’re a vaccine man. You love them. You know them.

Daniel: I am, I do. Um, there is not, unfortunately. As I mentioned earlier, there are these two types of hantavirus, the Asia-Europe one and the Americas one. There are some vaccines for the Asia-Europe form. Those are limited in use to just a number of countries, mainly China and Korea, and it only work against that sort of internal bleeding, kidney kind of severe form. It doesn’t work against what’s going on now caused by the Andes virus.

So there are no vaccines yet, or no licensed vaccines, there are people working on them, us included, but it’s not at a stage where it’s shown to work or be licensed.

Emily: Is there anything special about the hantavirus when it comes to making a vaccine that you need to look at, in terms of making it, than other illnesses out there, like measles or the Covid vaccine or something like that?

Daniel: Yeah. So much of making vaccines, the process is pretty similar regardless of what the pathogen is. Essentially, all a vaccine is – and there are loads of different types, and they all work in slightly different ways – really, all a vaccine is doing is mimicking the pathogen without causing sickness. That’s the only thing it’s trying to do.

So you vaccinate someone with something which looks like the virus, your body responds to it, but the vaccine itself isn’t making you sick. If it can do that, then you’ve got yourself a good vaccine.

There are a number of different approaches you can take. The most straightforward, in some ways, is just to take the entire pathogen, the entire virus, and inactivate it or kill it with chemicals or heat. That looks like the virus because it was the virus, and you’ve just inactivated it so it can’t cause disease.

Or you can take a slightly different approach, still taking the whole pathogen, but instead of killing it, you just weaken it slightly. That looks a bit more like the pathogen. It can still replicate, but it still can’t cause disease, as long as you’ve got a well-functioning immune system.

Then there’s a separate type of vaccine where, instead of taking the entire pathogen and killing it or weakening it, you just take a tiny part of it – a little bit on the surface of the viral particle. You include that in your vaccine, and then your body can respond to that little part. It can make antibodies against it. Then, when you see the actual pathogen, your immune system will respond only to that little part because that’s the only bit that it recognises. But that may be enough to disrupt the whole virus and prevent it from replicating.

It’s pretty similar whether you’re developing a vaccine against Andes virus or coronavirus. In the case of coronavirus, it was taking that spike protein which was on the surface of the viral particle and using that as a vaccine. This is essentially, we do the same thing, but instead of a spike protein, because there isn’t a spike protein, it’s called Gn or Gc. You take one of those proteins, encode that in your vaccine, and it’s the same thing, basically.

Emily: So we’re just not there yet.

Daniel: So, yeah, essentially we’re not there yet. Each pathogen has unique challenges. So sometimes we can try that approach and it doesn’t work because it doesn’t generate a protective immune response and then you have to go back to the drawing board and try and use maybe use a different part of the vaccine or try in some ways to make it more immunogenic.

Daniel: So we haven’t got to the stage – people have looked and are a bit more advanced on the development pipeline for Andes virus. Once you’ve made a vaccine, you can try and test it to see if it’s eliciting a type of immune response, perhaps in mice, and if it is, then you can progress from there. But yeah, essentially we’re just not there yet.

Emily: But I guess the question is, should I be anxious that we’re not there? Is this going to be the next great big pandemic? Am I, are we going to go through all that turmoil of Covid all over again?

Daniel: A crucial difference between hantaviruses and coronaviruses is that this is, it doesn’t transmit efficiently in humans – vastly less efficiently than Covid. The Covid virus it replicates…the SARS-CoV-2 virus, which causes Covid, replicates really efficiently in your throat and your upper airways. All it takes is a cough or a sneeze or just breathing to transmit that virus.

To transmit hantavirus, it replicates more slowly. It infects the endothelial cells around your blood vessels. There’s essentially less of it to shed into the environment.

And so how much virus is being shed by a person, and how likely they are to transmit, is affected by all sorts of different factors. It’s the intrinsic replication of the virus, it’s your immune system and how much that’s dampening it down, it’s how active you are, what you’re doing, and how close you are to a bunch of other people.

So there is a crucial difference between this and Covid in that it just doesn’t transmit in the same efficient way as Covid did. So it is a very serious disease, but it’s serious for the people who are infected. It’s less of a seriousness for there being sort of uncontrolled spread and all it takes is a passing moment and it’s just going to spread from person to person to person. That hasn’t happened in the same sort of frequency as it did for Covid.

Emily: So on a scale of one to ten, where one is, “I am not freaked out at all,” and ten is, like, “I am hiding in a bunker,” where should I be on the scale in terms of how freaked out I am by this?

Daniel: I would say a one or a two. I would be freaked out if I was on the cruise ship and I’d spent time with someone. Then, you know, there’s more of a concern. It is a disease that you don’t want to get.

But in terms of the concern for the general public, it’s very unlikely to readily transmit and spread, certainly nothing like how Covid did.

Emily: It doesn’t sound great.

Daniel: It’s definitely a disease you want to avoid. So you definitely don’t want to have it.So it is a serious disease. It’s known as a high-consequence pathogen. It is a serious outbreak, and it needs to be dealt with seriously by the people who are tasked with doing that. So UKHSA here, or the WHO – all of these organisations, they do need to treat it seriously.

But based on previous outbreaks, this isn’t something which is going to spread like wildfire.

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Emily: This podcast was brought to you by Oxford Sparks from the University of Oxford, with music by John Lyons, and a special thanks to Danny Wright.

Tell us what you think about this podcast. We are on the internet at Oxford Sparks, or you can go to our website, oxfordsparks.ox.ac.uk.

Get in touch. I’m Emily Elias. Bye for now.