TWiV 1365: Andes Virus Up Close

Introduction of guests and backgrounds

0:00This Week in Virology, the podcast about viruses, the kind that make you sick. Hello, ESCV. That's it. Very good. From ESCV 2026, this is TWIV. This Week in Virology, a special episode recorded on September 16th, 2026. I'm Vincent Racaniello, and you're listening to the podcast all about viruses. Today I am recording at the European Society for Clinical Virology in

0:37Porto, Portugal. And we're going to talk about the Andes virus outbreak on a cruise ship earlier this year. And I'm really lucky to have two guests who had played some roles in studying that outbreak for our discussion today. And so on my left, from University College London and the UK Health Security Agency, Catherine Houlihan. Welcome to TWIV. Thanks, Vincent. Thank you.

1:13And from Erasmus Medical Center, Corinne Gertz van Kessel. Welcome. Thank you.

1:24So let's get started. Before we talk about the science, I'd like to hear a little bit about your education and training, what got you here. So Catherine, why don't you tell us first?

1:38Thank you. Okay, great. I trained in Dundee in Scotland in medicine and did some of my infectious infectious disease and later infectious disease in general medicine initially training throughout the UK and spent in about 2007 a couple of years in South Africa doing HIV rollout, which is when I got interested in virology and epidemiology. And subsequently did my PhD where I spent a couple of years living in Tanzania studying HPV epidemiology and then returned to infectious disease and virology

2:11training properly in the UK before. But as I wrote up my PhD, the Ebola outbreak in 2014 hit and I was an infectious diseases doc who'd worked in some low-income settings, so was sent out with the WHO to do Ebola response. And I kind of kept doing that after that, as I completed my training and did some postdoc work with Emma Thompson from CVR Glasgow on metagenomics, to diagnose encephalitis in Uganda. And now I'm a 50% NHS virologist at UCLH and I'm a 50%

2:47infection doctor and virologist at UK Health Security Agency working at the Rare Imported Pathogens Laboratory, where we diagnose all the high-consequence pathogens in the UK. So you grew up in the UK? Yeah. And what made you decide to be a scientist? Do you remember? I think it was that, I think it was, well, medicine is science. And I think it was then the interest in just the sort of horrific effects that viruses can have on people that got me into sort of virology and basic virology and epidemiology.

3:23Medicine is science. That's what you said, right? Boy, we could have a whole discussion about that, but we're not going to do it today. No, no. Corinne, how about you? Tell us your background. So I actually did my complete medical education at Erasmus MC. So I started medical school there and I entered a PhD program in virology and pulmonary medicine, where I studied immunity against influenza viruses. Part of my study I did in France and I did also start my follow-up studies to become

4:00clinical virologist at Erasmus MC, where I started collaborating with Bangladesh and I spent some time in Bangladesh. And that actually mounted my interest for zoonotic infections. So once I started to work as a clinical virologist in the staff team at Erasmus MC, I started my research lines on emerging zoonotic viruses besides my clinical work and the work I do in diagnostic serology and virus culture. But actually, in my research, I really tried to link the fundamental questions towards

4:37the clinical questions. And the last years, we've really done that by trying to set up big cohorts of patients during different outbreaks. And in these cohorts, we try to answer the urgent questions like we are trying to do so in this outbreak. And what got you interested in science? Do you know?

5:02I think just answering the questions that you don't know. So like you said, medicine is science, science, but I think already, yeah, as a child, I was really, I grew up in Thailand and I already saw the interaction between humans and animals. And I think that there's a lot of things to answer there. So that's what I really like. All right, let's get to the outbreak now. Catherine, if you could just give us an overview of what

Overview of the Andes virus outbreak

5:28happened from the very beginning. Sure. So the outbreak we're talking about is Andy's hantavirus, which is good, just checking, which is a hantavirus, which is sort of asymptomatically carried by the long tailed pygmy rice rat and humans are usually infected by inhalation of the excreta of the animal. And this story unfolds on a cruise ship, the MV Hondias, which departed from the southern tip of Argentina on the 1st of April, traveling towards Cape Verde through multiple islands. And very

6:05early on in the trip, on the 6th of April, or various dates are reported, but around about the 6th of April, the first case becomes unwell, dies on the 11th of April on the ship and the ship carries on its journey. And subsequently from the sort of 20th, 21st, 22nd onwards, there's another two cases, one of whom also dies. But after being, after coming off the boat, another individual, this case three becomes unwell after coming off the boat. But the boat continues to sail on. And

6:36at some point, the flag is sent that there is a respiratory outbreak here, the death, I should have said in the first case was a severe acute respiratory illness. And diagnostics are then performed to identify Andy's hantavirus. And we end up with 13 cases, three deaths, and sort of over 300 contacts of the case spread around 33 different countries and overseas territories. So a huge exercise in global public health, which has ended and been declared over by the WHO.

7:10I just looked it up this morning, the MV Hondias is on its way to Greenland on another cruise. So it's still in business. So we've had experiences with hantaviruses before, right? They're typically zoonotic infections, right? But they don't establish long change of infection with the exception of Andes, right? So Andes is the only hantavirus that is person-to-person transmissible. There are multiple other old world and new world hantaviruses. But this is the only one that has direct human-to-human

7:43transmission. And that's what's happened in this case. So Corinne, the index case, the man who initially became ill, he and his wife had been trekking in Patagonia for a long time. And it's thought that's where they got this exposure to the rice rat and Andes virus. So how certain are we about that? Is there any actual evidence for that? Yeah, so the information comes from their travel logs and the information we got about their previous travel. The interesting thing is that it's not only this couple that traveled before entering the ship.

8:18A lot of other people that actually went on the boat have traveled through South America. But in the end, yeah, they have genetically compared the viruses in the people that were on the boat and got sick with the viruses that are circulating in animals that are on this track that they traveled. So it's very highly suspect, let's say. But they have not isolated viruses from the animals on their route yet? Yes, that's ongoing. That's currently ongoing. Yeah.

Incubation and transmission dynamics

8:50So Catherine, the two individuals presumably boarded during their incubation period, right? How long would you say they were incubating before the first symptoms, which are April 6th, right? Yeah, yeah. So the incubation of this Hantavirus is up to 42 days. The usual, the average incubation is 18 to 22. So this individual, case number one, was incubating during the time of probably of boarding.

9:24The partner, the wife, who is the second case, actually sort of acquired her illness probably around 18 days after the onset of symptoms from the index case. Around about there are different dates that are reported, as I said. So it's likely that this is the index case. She is a secondary case from person-to-person transmission. So she incubated on the ship from the transmission there, although we cannot be certain. Her, you know, if you count backwards, looking at where they have both acquired this infection,

9:57there is some, there have been suspicions for different places, right? So Tierra del Fuego has been suspected as a place. They were all together doing some bird watching on this big site. But there has been animal sampling, I understand, of that area. And they haven't found the long-tailed pygmy rice rat, nor any of the exact sequences. No, exactly. Not in that specific area. So the question is, which area specifically is it, and who of the people were exactly at these areas? Because this couple traveled in a camper, so they visited several areas. But it seems that it's really hard to know if she didn't get infected herself on land

10:33because the incubation period is so long, right? Can be up to 42 days, yeah, but it is usually shorter than that. Yeah. So do we have virus on both of them to be able to compare? Exactly. So we don't. So the index case actually died on the ship. And as ships do, have a mortuary carried the body before disembarkation. And the body disembarked with his wife, who was then making her return journey. And no sampling at any time, because it was not until there were three cases that the suspicion was flagged.

11:07And I think actually a bit of credit to the South African doctors who picked up the case that they, once the signal had been sent that this is possibly a cluster, rescued samples before they were discarded from the wife, from the case number two, which is just in time so they could be tested for Andes virus because she obviously died, I think, in a resuscitation area of emergency room in Johannesburg. So we do have samples from her. We have samples from her. Were they sequenced?

11:37Yeah, they have been sequenced, yes. So we know that was an Andes antivirus. Okay, so then we have to match them to the rodent isolates if we ever get them, right? Yes, definitely.

11:47So Corinne, oh, one more thing, Catherine. So this is all assuming that people are infectious during the incubation period, if she got it from him, right? Because it's not the case for all viruses. Yeah, it's really interesting. And this is the question about infectiousness during the incubation period is a key question for clinical virologists and people doing public health and sort of virus control, isn't it? So we know that people are viremic before they are symptomatic.

12:18And the symptomatic time is the prodrome of the illness, it's called the prodrome. And having detected virus, I suppose you could postulate that they are infectious. But the virus has been detected in some really nice follow-up studies done in Chile, which we lent on heavily during our understanding of this outbreak, published in 2008, where they followed up 470-odd contacts of 70-odd cases, a really nicely designed study that gave us the kind of information that people are viremic before they're symptomatic

12:51from 5 to 15 days before they're prodrome. So we took a pragmatic approach at UKHSA, assuming people are infectious 48 hours before they're symptomatic. But we have no real evidence of that kind of transmission. And we do have evidence of transmission during prodromal illness. So to put together the pathogenesis, this is an inhaled pathogen from rodent excreta. Yes. Presumably it reproduces locally in the lungs and then establishes a viremic phase. Yes. Does it go to other, any tissues to reproduce?

13:23Do we know? It's replicating in lymphoid tissues, I think. Yeah. And then causing this disseminated viremia, particularly located in throats and salivary glands. And that's how it's transmitted to others. Yeah. I think the transmission is really difficult to identify how two people in close contact actually transmit a virus. So there's good evidence of sexual contact, not necessarily through sexual transmission, but presumably through kissing and very close contact and sort of less strong evidence, but still evidence of household transmission from people that are not sexual contacts.

13:57And even, interestingly, again, leaning on data from Chile, transmission from a mother to her 10-year-old daughter through the household contact and close physical contact. The exact mechanism of that is unknown. But we do detect it in saliva. We detect it in cravicular fluids and nose and throat swabs. So the virus is there. There was a birthday party in Argentina, right, where people presumably transmitted it through droplets or aerosols, whatever, right? Yes. Yeah. Corinne, so from the genomic evidence that we have, there's no more than one SNP difference

14:33per case. I don't know how many different evidences we have like that, but what would that mean? Yeah, so what we can learn from that is that the viruses are very similar between the different patients that we have detected.

14:52Yeah, so that makes it very likely that this virus has spread from human to human. But of course, it's not excluded that these people might have visited the same site as we already discussed and have gotten infected by the same virus. But I think it makes it very likely that there has been transmission on board. And specifically for the three later patients that got ill quite far after this incubation period that we just mentioned, the 42 days, I think these three, it's almost not possible

15:23that there was another route of infection unless, of course, there would have been rodents, for example, on board of the boat. But that has been, well, almost completely surely excluded. How many, from how many patients do we have sequencing, do you know? I think we have them of almost, well, I'm not, I can't say the exact number, but almost all the patients where we have done PCR confirmation.

15:55So that's, I think, 12 out of 13 because the index case didn't have material. Yeah.

Investigating potential rodent sources on board

16:02So Catherine, Corinne just mentioned this idea that the alternative is that there were rodents on the ship, you know, because they can climb in over the ropes and so forth when they're in port and they actually started the outbreak. What's your thoughts about that? Yes. The two reasons why that's less likely. Ships are really, I mean, ships have been transmitting pathogens around the UK, around the UK, around the world since the Black Death, since they carried plague on the, through the fleas. So there are rat guards.

16:32So rats are now unable to sort of ferry up and down these, these ropes. And there are certificates, which used to be called de-ratting certificates that ships had to have, which I think is a great name. It's not called that anymore. But there are, there was actually an inspection in this, one of the South Georgia, which is one of the first islands the ship came to, through a sniffer dogs, which didn't locate any rats. So there are, ports are very invested in making sure these ships, which bring people and pathogens to their shores when they have their distant islands, they, they have, they invest quite

17:02a lot in safety and protection of ships. So I think, I think there's a lot of evidence that goes against that. And actually I was quizzing Corinne before about whether there's any evidence of virus on the ship, because that would be a useful, you know, if it's in the bowels of the ship where the rats might be, then maybe that's interesting. So I'll let her take that one. Yeah, well, up to now, there's only very little evidence and specifically not of any rodents being present. And there's also been done very extensive environmental sampling of dust, for example,

17:37and to see if there's any environmental genome being detected that could not be detected at the size where they were looking for it. And besides that, there has been very extensive sampling and there has been found some genome, some viral genome in the rooms of the people that were actually ill.

17:56But there's no evidence up to present that that was, that there were any rodents on board that have... No, essentially. So there were genomes in the sick people's room, but not other rooms. As far as I know, it has only been contained into the rooms of the people that had been ill and the rooms have not been cleaned.

18:19By the way, these cones, you're talking about these cones on the ropes. I've been told that rodents are very clever. They can go in and go around them, you know, but I just don't know. It's not my area. So, Corinne, we've seen Andy's virus spillover before into people, limited outbreaks, but we've never seen an outbreak on a cruise ship before. So what was it about this specific incident that this happened? To be honest, I think it was just very unfortunate because I think the spillover from animal to

18:56human is quite rare. It might be that we are under-diagnosing, of course, that there's not often thought of it, but still, I think it is quite rare. And then the chance that it spreads from human to human, as we discussed, is also not very likely. But of course, if you enter a cruise ship with an infected person, that is the ideal situation. You don't need a super spreader event or a big party because you are all closely together. You use the same rooms.

19:27You spend a lot of time together, usually. And yeah, I think it's just very unfortunate that these people traveled and entered the boat. Do you think it had anything to do with their age and, you know, the fact that their immune systems were subpar? They spent a lot of time walking around, maybe got a big viral load or anything like that? I think that they did travel, of course, to areas where perhaps there was quite a lot of this virus. But in the end, it will not have been their age that have made them more susceptible for

20:00the spillover, I think. And that's also what we see in the different patients that got infected. It's not, it was not only the elderly population. It's, I think, more about the amount of exposure and how close are you getting with other people. Because, right, it were the doctors, the guides, the people who really had close contact with the index cases. So I think that that's more important.

Medical challenges on the cruise ship

20:26So Catherine, this ship had one doctor, probably limited medical facilities, band-aids, not too much. I mean, this is going to deal with abrasions, cuts, and minor things. I often think about how this doctor must have been totally overwhelmed by this, to have someone actually die. But anyway, by the time the symptoms were recognized in that first individual, do you think it's likely that transmission had already occurred to others? This goes back to the transmission question as well, right?

20:59Yes, I imagine so. I mean, particularly to the wife sharing a cabin, but potentially also to other individuals. And you told the story of the birthday party. I mean, and, you know, we've all done it when we have attended somewhere where we've been feeling not quite right, a little bit unwell, a little bit symptomatic. And I think this is probably what this individual and what, you know, lots of individuals in a completely understandable way would do. And I think that's when the transmission can happen. So I think, yes, this is a bit too early. And maybe the lessons here are that if you're on a cruise, if you're in an enclosed space

21:33and you start to feel unwell, that's the time to maybe isolate. Because if this was any of the pathogens that would have been suspected, like influenza, COVID, then you would ideally isolate and not sort of pass it on. But I think we just don't, as humans, we're sociable animals, aren't we? I think the lesson is you never go on a cruise ship. Which we already knew from norovirus, right? But I've often thought of the fact that if these two had been on land where there were

22:06proper hospitals, maybe their lives would have been saved by being intubated and therapies and so forth. Just you can't do much in a cruise ship. And I think that's the thing that was difficult is that the cardiopulmonary syndrome of Andy's hand virus progresses very quickly. And so you need to be sort of close to facilities, ideally. So that's one of the reasons why this outbreak was incredibly difficult. I remember the first outbreak of Sin Nombre in the US, 1993, I think.

22:40A lot of the initial victims were very healthy young people. And it just overwhelmed within days. So very quickly. So I'm curious, when did your countries get involved? Catherine, when did the UK get involved in this? Fairly early. So the UK has these UK overseas territories. And so it was a Dutch ship. But I think that actually we have to give a bit of credit to one of the doctors on the Ascension Island who flagged that as he was assisting the disembarked case, the case number

23:16three, who then was flown to Johannesburg in an emergency repatriation, well, an emergency transfer to a high-level centre, and then said, I think this individual, I think there was two people on the ship. There's a guy that died of respiratory illness. There's a woman in South Africa. There's a cluster here. Talked to South Africa. And again, excellent coordination. And then spoke to the medic, who is a UK HSA employee who looks after the UK overseas territories and provides microbiology support to them.

23:46So got everybody together and said, we've got this cluster. And that's when UK HSA started to get involved. What was the date on that one? That would have been in May, early May. Okay. And what about you? When did you get involved? Well, I think for the Netherlands, it's indeed interesting because, of course, the ship had a Dutch flag, but also there were guides on the ship that had previously been collaborating with some of my colleagues at Erasmus for the bird sampling in Antarctica. So before that, anything came out in the public, there was already text messages going on, like

24:22there's someone ill, maybe it's bird flu. So actually, the idea was really more focusing towards flu in the beginning. But that was the unofficial route. Of course, after that, we soon came involved, I think, together with the UK once the patient was in South Africa. And there was a consultation with a bigger group of people. But the crew was also Dutch, right? The whole crew? Not the whole crew, because there were a lot of Asian crew members, actually from the

24:53Philippines. But I think, yeah, there were a lot of Dutch tour guides and people involved in the organization. Were there UK nationals on the boat? Mm-hmm, yes. So that would have been another reason you would get involved, too, besides the islands being UK territory. Okay. So, Catherine, the ship sailed April 1. The man gets sick on April 6. WHO doesn't say anything until May 2. So why do we have this delay? Do we know? It's because, I mean, I think a death on a cruise ship isn't terribly unusual.

25:28I mean, it's unusual. But, I mean, these ships are at sea for a long time. The ships harried mortuaries. Prepared for this kind of thing. The age of the population on a cruise ship is usually a bit older for this type of cruise. And I think, so the one individual may not have flagged. The cluster then was, you know, the people had disembarked. So then the cluster is picked up through these disparate ways towards the very end of April. And it's just that long incubation. So if we think that the wife had caught the infection from her husband, 18 days later, she starts to become symptomatic.

26:02And then she actually passed away in Johannesburg. And so it is that it is that delay. And I think the WHO, to their credit, I think, responded very quickly. So there was this coordinated call about differential diagnosis and a rapid testing in South Africa, identifying Hantavirus. And then the WHO pulling this flag very quickly soon after that. So I think it's the nature of the beast. So the ship is making multiple stops after it leaves. It goes to South Georgia, Tristan da Cunha, St. Helena, Ascension, as you mentioned.

26:37Did any of them notice anything going on? I guess Ascension you said already, but any of the others? Yeah, I don't think so at that point, because it's St. Helena and Ascension Islands where these individuals had disembarked and well initially. Right. So the index dies on board April 11, correct? Yeah. Do you know what the cause of – what were the differentials at that point? Do we know?

27:08Yeah. I mean, presumably the doctor is thinking, like you mentioned, bird flu, we've been in contact with a lot of animals. Bird flu – so any of the avian influenzas, the highly pathogenic avian influenzas would be on your list. But sort of blue in a late 60s, early 70s-year-old, which I think was the index case. But also, I mean, coronavirus, SARS-CoV-2. But there are bacterial pathogens you'd probably have to consider on a cruise ship in an enclosed environment. And legionella, mycoplasma, severe strep pneumonia could kill people of that age.

27:43It can kill anybody from a pneumonia very quickly. And of course, you don't have an x-ray, so you don't know whether this is a lober pneumonia or a viral pneumonia. You have limited facilities to do any kind of diagnostics. And don't forget virus X. Virus X. A new one, right, that we haven't seen before. Yeah. So, Corinne, I'm curious about the tests that were done. What were the first tests and where were they done and how did that work out? So, I think the first laboratory testing was done on the patient that was transferred to South Africa.

Laboratory testing and genomic sequencing

28:21And they, of course, did their panel of respiratory viruses. So, it was PCR testing. And, of course, the broader diagnostics. But, yeah, in the end, the Hanta virus was detected by a PCR. And, of course, then, subsequently, they had to do rapid sequencing, yeah, to identify the exact strain. But with a patient with this kind of symptoms coming from South America, I think that the clue was quickly towards on this virus.

28:51And it's good to mention that Institut Pasteur and Dakar, they were actually the lab that has confirmed the second and the third case, if I'm correct. But they were involved very rapidly as well. So, this is May now. We're talking about May 2nd-ish. May is when the people went to South Africa. So, the PCR, so it's part of a panel already. The Hanta virus is not usually in the respiratory panels. So, you have to specifically think of that. But I think it was mentioned in this consultation.

29:24So, I think there was a big group of experts coming together and looking into the differential diagnosis. And then South Africa did the testing. And I think it's really good to mention that there was some discussion about how fast all the sequences came available. But I think that, in the end, it was done very, very coordinated. And strains have been shared to do it really clear. And that's why we, in the end, know so clearly that there was only this one SNP difference.

29:55So, I think, in the end, it was done really efficient and in a collaborative way between all the different reference labs. That was quite interesting. And so, there's a Hanta virus PCR primer set which will work for the various Hanta viruses that we know of, correct? Yeah, you have a pan-Hanta virus PCR and you have specific on this virus PCRs as well. So, once we knew that it was on this virus, people started using the specific PCR. It's interesting that they suspected it because of the origin of the cruise, right? Is that what you said?

30:27Well, I think as a clinical virologist or as a virologist, you start combining the different options. And, yeah, in a patient where respiratory symptoms are an important part and you have this, you seem to have a person-to-person transmission. So, you start thinking in the direction of viruses and it's not in your straightforward panel. Yeah, you have to start thinking a bit out of the box. And then, I think, with people who have traveled in South America, it should be in your differential diagnosis.

31:00I mean, that's the key. It's so rare, but still you have to keep it in the back of your mind, right? Yeah. Yeah, that's why I think that it's so important to have these networks of international researchers and virologists because, of course, obviously, in different parts of the world, there are different things you have to think of. And, yeah, I think that this one really shows that you have to combine different expertise and people to do this. So, sometimes when you hear hoofbeats, you have to think of zebras.

31:34Yeah, I think so. I mean, they say, you know, just think of horses. Don't get too crazy, but sometimes you do. Yeah, or the unknown, right? That's also important, as you said. It might be something we don't know. I think we answered this, but let me ask you anyway, Catherine. How was it then identified as Andes? Yeah, I think it was then sequenced. Yeah, I mean, we at the rear import of pathogens have specific PCRs. We would use a kind of an in-house developed from a couple of published recognized PCRs.

32:08But what was really useful when the sequencing came out is that our team will have compared that sequence to the PCRs that we have. So, then when we're receiving people in the UK as contacts and need to test them, we know the sequence and we know that our primate probes will pick it up. So, Corinne, is it safe to say that all the testing was done offshore, not on the ship? Yes, that's correct. There was hardly any testing on the ship. Perhaps, at the end, there were some rapid tests taken on board, but there were no Andes virus rapid tests that could be done.

32:44Right. Go to the CVS and buy a Hantavirus rapid antigen test. Can't do it.

International contact tracing and logistical response

32:52Catherine, from the UK perspective, what were your key concerns?

32:58I think with this particular virus, it has a long incubation period. And so, that is a first major concern. These contacts, possibly incubating, are to be followed for a significant amount of time. And so, that's the, first of all, slightly galling aspect of this. The other challenge, I suppose, is that, you know, you've got an isolated group on a cruise ship. It'd be lovely if they just all stayed on the cruise ship, but they did not. So, there was, you know, these two individuals who became symptomatic on distant islands, St. Helena and Ascension Island.

33:32Which we can now all point to on a map, but previously would have struggled. And these individuals have then been symptomatic and made bunch of contacts on the islands. Then they have got on international flights and had contacts on the flights. And these contacts have then dissipated around the world. So, logistically, it's huge. It's a huge expanding outbreak. And we know the person-to-person transmission is minimal, but we know that these people have been sitting next to the prodromal unwell. And there's person-to-person transmission. And the case fatality is 35-odd percent.

34:03So, up until the point when we know the causative agent, you can't stop people from going where they want to go? Is that the idea? Yes. Yeah. You can't. I mean, we can't really stop people continuing until you know there's Hanta. And then, even then, stopping people from continuing their lives as they wish is, you know, really challenging. Apparently not in the U.S.

34:31No comment. Corinne, from the Netherlands perspective, you have a Dutch ship with Dutch crew. What are you concerned about?

34:44Well, obviously, a lot of the same things. But a worrying thing was, of course, as well, how to handle the ship once it would come to the harbor. And how, yeah, all the guidelines and how would we clean the ship? How could we sample safely? All these questions. So, the ship was a big thing, but also the crew that was there and came from, partly came from Asia. Yeah, they had to be quarantined in the Netherlands because it was part of the Dutch responsibility.

35:15So, this quarantine thing was complex, but I think very well and structured done. And I think everyone really accepted their quarantine and everything. And they really tested all the tests they had to do. So, I think that went really well. But another challenge as well was, I think, the infection prevention in the hospitals. Because in the Netherlands, we had a bit of a – well, we had some events there. Because, obviously, on this virus, people don't have experience with it.

35:48So, it's not like you have to handle like you have an Ebola patient. But also, you do need to be careful. So, there were some small exposures. And, of course, because you're not really sure about the infectiousness of the samples that you're working with, that gave some stress to the employees.

36:12So, Catherine, you helped with medevacking from the Canary Islands, correct? So, I want to ask you about that. But first, why did the ship stop there and decide to disembark? Yeah. I mean, the Canary Islands is a great transport hub to repatriate to the Netherlands, back to the UK. Great transport links compared to its destination island of Cape Verde, compared to multiple other islands. And so, Tenerife made sense. It has high-level medical facilities, in addition, for anyone becoming unwell.

36:46So, tell us about your experience. They sent you there by yourself, right? So, what did you do? That's funny, because I said to Vincent not to say. I'm kidding. So, I did – so, there were UK contacts who were medevaced by others, by my colleagues the day before. I was actually assisting the Netherlands, so the Dutch repatriations. And I think partly because you guys had quite a busy time with cases and with repatriations, and we in the UK had no cases.

37:18And so, our high-consequence infectious disease-trained medics are sort of more available than maybe your team were. And so, there was a request for repatriation assistance. And so, I travelled to Tenerife to repatriate 25 contacts. And that was – yeah, I mean, I think you're alluding to sort of this thing of doing it on your own. So, I think all of us who've worn PPE and taken it off safely, and I mean sort of high-consequence PPE, high-level PPE, need to have somebody watching to check that you're not going to contaminate yourself.

37:55And my job was basically to sort of medevac and look after these individuals who were at kind of peak incubation period time for developing symptoms. So, had somebody developed symptoms on the plane, I would have been the first point of contact. And had they even developed the prodrome, the infectious stage, I would have been being very careful. And ideally, I think the thing that I'm taking away from this is maybe two people need to do this, one of whom is a trained individual. My plan getting on the plane had been to train one of the aircrew.

38:25The aircrew were absolutely brilliant. And they obviously deal with quite a lot of infections through aircrew because people often get unwell on planes. But quite a difficult training scenario compared to other people I've trained on sort of doffing PPE and things. But, yeah, a great experience. Well, you obviously did it right because you didn't get sick, right? Actually, and I got a phone call 48 hours after delivering my cargo that none of them had become symptomatic. So, I think I was good. Very good. So, looking back, is there anything you would have done differently?

Quarantine management and medical evacuations

38:57I think that it was really interesting, too. So, all these individuals came off the boat. They had to wait on the boat for an extra six hours or so. So, I spent a lot of time just hanging out on an airplane, which is an interesting experience. And it was too rocky or something for them to come. Well, they eventually came off and filed in and sat, you know, one person on a row. And I hadn't planned this, but I suddenly thought, wow, if one of these individuals then becomes a case tomorrow or at least becomes symptomatic, I'm going to want to know where they sat.

39:27So, after they'd sat down and we'd all sort of got ready, I then decided to make a list and draw a map and all this kind of stuff. And it was quite interesting trying to think about quarantine. So, I ran through scenarios of if one of these individuals gets sick, they're going to the back row where I've cleared three rows. This will be the sick bay. This will be their toilet. They won't use any other toilet. The crew will use the front toilet. The other passengers use the back toilet. All of these things. Well, they picked the right person, right?

39:56I mean, we didn't have to test it. But hopefully. So, Corinne, when the evacuation happens in the Netherlands, what are the patients like? Are they very sick?

40:08So, there were two patients that were admitted in the Netherlands and one patient was transferred to Germany. The two Dutch patients, they were symptomatic but not that severe that they needed respiratory support or ICU care. But they were kept at the hospital. They were tested on a daily, no, three times a week, if I'm correct. And, yeah, they were carefully monitored. But, actually, they were relatively stable.

40:38And it was more that we were worried about the high viral loads that we measured. And we wanted that to go down, at least in the respiratory specimen. Besides, we wanted to monitor their symptoms because sometimes you can see that very quickly it can get more severe. But that did not happen. So, given that there's a long incubation period, right? Were you confident that you could keep track of these patients? Well, I think we were quite sure that with the 42 days, we were at the safe side and following up.

41:10I mean, it was quite shocking, of course, when one of the – so, in the Netherlands, we had one of the patients that was in the follow-up that tested positive. So, we did feel like, okay, we were doing the right thing because we're testing them on a weekly base. And so, the patient developed symptoms when we already knew that it was positive. So, it was – we felt that we were doing the right thing. And, yeah, I think with the period that we took, we were really – we felt we were on the safe side. And I'm happy that it went like it went.

41:43So, we heard the incubation period, one to eight weeks. Do you have any sense for why it would have such a broad range? Yeah, so that's a very interesting question. I think we are still trying to find out how exactly the virus – yeah, what exactly it does. So, what is the exact cell tropism? We know some of the cells that get infected, including epithelial cells, but also dendritic cells. We are also a bit wondering why there is this very long viremic phase in whole blood specifically.

42:18So, it is very hard to say because, yeah, the immune response comes up very efficiently. We are not able to culture the virus very easily. So, there is something going on with the virus where it can somehow, yeah, perhaps hide from the immune system. Or we don't know that yet. So, there's still quite some questions to answer there. Any thoughts on that, Catherine? Yeah, I agree. It's an area for development. And it's in the list of questions that we wish we understood better.

42:49I think the 42 days is the maximum. I think the mean incubation being 22. And then if you think back to my previous comment about the 5 to 15 days before that, but people can be viremic, then you're really bringing it back down to the exposure time. I think there's this very early viremia. And then interesting lessons from sort of discussions we've had actually with a Chilean professor, Pablo Villal, who came and joined our imported fever service educational meetings. And we discussed a case and he was sort of saying that this virus isn't lytic.

43:22It's more a functional disorder that it causes in the epithelial lining. Hence, the cardiopulmonary syndrome happens because the membranes become leaky rather than it causing a lytic infection. So, I think it's the danger of the immune system later on rather than the virus itself. I think we tolerate the virus until we don't. So, talk about the lab results as you saw them come in. Were there any surprises? I mean, from the UK point of view, we actually, I mean, we repatriated.

43:54We had 85 high-risk contacts scattered around, but we had 35 individuals in our Arrow Park isolation because they weren't able to isolate and they were high-risk contacts. And these individuals had the weekly, same weekly. ECDC came out very quickly with some nice guidance. We decided to do the similar action of a weekly PCR and nose and throat swab. And none of our individuals were positive. So, that was very reassuring. And serologically, using an anti-specific Liza are not seroconverted.

44:25So, we think we've got them out. What was really interesting, I mean, a couple of interesting things is that we repatriated a Brit back from the Netherlands. And we were testing slightly different fluids. So, you guys did cravicular fluid and we did nose and throat swabs. And we find a bit more virus than you guys did. And it's, you know, you run a PCR in different labs and you will find a different CT value. And one laboratory will say, oh, I think we need to not put that person on the commercial. You know, we need to use our high-level PPE and do a bit more of isolation than maybe was being done.

44:58So, really interesting comparative public health virology there, which is really interesting. But there is one other really interesting result, which is from an individual who doesn't currently count as a case. I'm really interested in Corine's thoughts on who is the healthcare worker who had a transient viremia, but did not seroconvert. Yeah. And I wanted to grill you about your laboratory results from that. Yeah. So, in the Netherlands, we have done testing and we have two, we have a combined reference lab at Erasmus MC and the Institute of Health, the National Institute of Health.

45:32And so, we did combined testing of the positive cases. And this was one of the suspect cases because he was a healthcare worker and had possibly had some contact, which was not completely conform to the guidelines. We tested this patient and in one of the two labs, there was one PCR result positive with a very high CT value, so a low viral load. And obviously, the PCR protocols were slightly different between the different labs.

46:03So, there's always a bit of discussion about sensitivity of the assays. And so, it could not be confirmed at the other lab. So, in the end, we didn't have enough evidence to say this has been an exposure. The patient did not seroconvert. So, we didn't have enough tools to say this was a real exposure. But I think there are some mixed thoughts about it. If this can indeed happen to be very transient, short-term viremia, but yeah.

Surveillance results and global cooperation

46:36So, the ship comes to Rotterdam May 18th, right? We've talked a little bit about this surveillance. Was there any evidence that there were multiple waves of infection or just index case to others and that's it?

46:51I think that that cannot be concluded with a lot of certainty because obviously, the viruses that were sequenced were all very similar. And, of course, there have been other interactions. It was not only the interaction with the index case. So, I think it's very likely that there have been multiple contacts between people that have caused the spread. So, Catherine, you said earlier that you were in contact with some Argentine scientists because they've had experience.

47:24What did you learn that was useful? Well, first of all, there was a lot of offering of sharing of lab reagents and lab protocols and ELISA plates and really, like, amazing offers of support to the countries affected. So, really nice offers from Chile and Argentinean scientists. And I think the key bits we were learning were about the kind of pathophysiology of the disease, which, thankfully, we in the UK didn't need to deal with. It was really interesting insights into how best to look after these patients and an argument that antivirals, which, in the end, were used in quite a few of the cases from the Hondias, were too late.

48:04They didn't see them making a difference to the viral load during illness. It was more, you know, ecatabant as a sort of immunotherapy specific to the pathophysiology of the virus. But some really useful thoughts throughout the whole event. International cooperation. It's good. Beautiful. Corinne, if there were tomorrow another pathogen outbreak on a cruise ship and you got involved, would you do anything different? Well, I think we did quite a good job.

48:40And I think from the outside, it's always easy to comment on things that we should have done differently. But, yeah, I think, again, the cooperation and the international contacts, that was all very good. And I think that's something that we really need to maintain and also the role of the WHO overseeing all these different tasks. I think that's a very important thing. And, yeah, obviously, if you want to do something better, you can think of rapid diagnostics or perhaps sending out material.

49:14But it's really hard if you're on this ship, obviously, to make these decisions also for the clinicians that are on board. So I think it was all. There was a lot of things that went well.

Preventive measures for future cruises

49:27So, Catherine, for cruise ship operators, is there anything new that they should be doing based on this?

49:34I mean, I think following the guidance, I think there will be an examination further of what they can do. There is a lot of regulation and a lot of guidance out there. I think even the ventilation systems, which we were discussing, seem to be quite robust within the cruise ships. Perhaps it's just revising their protocols. And perhaps it is that reach out when there's a death or when there's a serious illness on board, that kind of not assuming that it's some common pathogen to maybe think about, well, this is a, you know,

50:05if the individuals have been particularly mixing in rural areas or trekking and doing sort of an expedition cruise, these are the cruises that maybe we need to think about. But equally, I mean, they always have problems. The Diamond Princess had problems with COVID. And you've mentioned Norovirus as the primary reason. And I think I would like to add that the operator of this ship, they were really open for all the studies and open to examine what was going on. And also, I think they had their things really well organized,

50:35including the information they gave to people about zoonosis and that kind of thing. So, I mean, that's an important part, of course, that people are aware of risks and zoonosis and infections. So, I think the ship was quite, yeah, doing it quite well. So, do you think that cruises that originate, say, from Patagonia, they should warn passengers of risks or even ask them where they've been, you know, the previous months? Yeah, I think a lot of these kind of cruises, they attract people that, of course, like nature,

51:09that are interested in the areas where they're going. And I think this is already a topic that they discuss on board. But, yeah, obviously, I think that's important because it all starts with awareness. But I think in these kind of cruises, that's already part of the talks they have and the information they give. So, Catherine, hantavirus monoclonals have been made. In fact, we've done multiple TWIV episodes on them. Would they have been useful for this outbreak?

51:40I mean, yes, they have been made. I think particularly the Andes monoclonal has got some hamster model evidence, doesn't it? But they just, they may have been, they appear useful in treatment of cases particularly. They could be useful. And like we've discussed the sort of antiviral nature, is that too late? Are they useful? I think they could be useful in post-exposure prophylaxis potentially. They were not available and they are not, I mean, they haven't been through the safety testing that you would require to use them even experimentally, I think, for Andes.

52:12And so I think that wasn't the choice we made. I mean, we actually did use post-exposure prophylaxis in the individuals who were high-risk contacts or at least offered it to individuals who were high-risk contacts. Favapiravir was offered and taken up by several of them. 19 individuals in the UK took a course of Favapiravir. Whether that made any difference to the lack of prevention, they were all high-risk contacts, whether they did anything. But I think it's an area for future research, isn't it?

52:42Monoclonals versus antivirals, what should we be using in post-exposure prophylaxis? And it's a question that comes up for all of these emerging infections, including Bundabugoo, what have we got for post-exposure prophylaxis? Not very much. And that's where I think we need to start thinking more, carrying out more research in that area. Corinne, what one uncertainty about this outbreak would you like to see resolved?

53:09Yeah, so personally, I'm very much interested in learning more about, well, the infectivity, but also the immune response of the individuals. So what we have tried to do is to collect BBMC, some mononuclear cells of the individuals that were infected over time, so that we can really study their B and T cell responses and look into cross-reactivity against other antiviruses. But, I mean, that's, of course, a personal interest of mine, because I think in every outbreak you should see if you could learn something new of it.

53:43So that's my personal interest. Catherine, this outbreak got a lot of international attention. Why is that? Yes, it did, didn't it? And I think it's because it reads like a horror story almost. It reads like a, you know, man dies, wife gets sick, other people get sick. And the individuals had to spend such a long time on that ship, and the ship still continued with the crew who dropped off at Tenerife and then continued to sail that ship back. So I think scary virus infects, you know, people traveling on a cruise ship is interesting press.

54:20But I think coming back to other things we've heard, there's a responsibility for all of us to kind of correct the trajectory on press and discussions so that it becomes helpful and not just kind of scary.

54:34Irene, what would you have done if you hadn't become a scientist? I think I would have become a journalist, actually. Cool. You may have covered this outbreak. Who knows? How about you, Catherine? Yeah, that's a good one. Investigative kind of journalist or detective. Solving crimes. You could do the same thing? Solving puzzles. You would do the same thing? I would, I'd go, I'd go detective. I'd go solving crime. Well, you could work together.

55:05We can continue. And you could have a nice TV show about it. I think those exist.

Closing credits and acknowledgments

55:12All right.

Closing credits and acknowledgments

55:13That's a special episode of TWIV from ESCV 2026. You can find the show notes at microbe.tv slash TWIV. If you enjoy our science programs, we'd love your support. You can go to microbe.tv slash contribute. My guest today from University College London and UK HSA, Catherine Houlihan. Thank you so much. Thank you.

55:39And from Erasmus Medical Center, Corinne Goertz van Kessel. Thank you so much. I'd like to thank ESCV 2026 for having TWIV, especially President Heli Harvilla and Conference Chair Maria Alexander. I'd like to thank the American Society for Virology and the American Society for Microbiology

56:09for their support of TWIV, Ronald Jenkes for the music, and Jolene Ramsey for the timestamps. You've been listening to This Week in Virology. Thanks for joining us. We'll be back next week. Another TWIV is viral. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you.

56:39Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you. Thank you.