TWiV 1365: Andes Virus Up Close

0:00Catherine Houlihan: This 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 Porto, 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.

1:05Catherine Houlihan: Welcome to TWIV.

1:06Vincent Racaniello: Thanks, Vincent. Thank you.

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

1:24Catherine Houlihan: So 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?

1:38Vincent Racaniello: Thank you. Okay, great. I trained in Dundee in Scotland in medicine and did some of my 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 training properly in the UK before but as I wrote up my PhD the Ebola outbreak in 2014 hit and I was a infectious diseases doc who'd worked in in some low-income settings so was sent out with the WHO to to do Ebola response So I kind of kept doing that after that, whilst I completed my training and did some post-op work with Emma Thompson from CVR Glasgow on metagenomics to diagnose encephalitis in Uganda.

2:40Vincent Racaniello: And now I'm a 50 % NHS virologist at UCLH, and I'm a 50 % infection 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.

2:58Catherine Houlihan: So you grew up in the UK?

3:00Vincent Racaniello: Yeah.

3:01Catherine Houlihan: And what made you decide to be a scientist, do you remember?

3:06Vincent Racaniello: 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.

3:23Catherine Houlihan: Medicine 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. Corinne, how about you? Tell us your background.

3:36Corinne Guerts van Kessel: 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 a clinical 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.

4:30Corinne Guerts van Kessel: But actually, in my research, I really try to link the fundamental questions towards the 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 try to do so on this outbreak.

4:54Catherine Houlihan: And what got you interested in science? Do you know?

5:02Corinne Guerts van Kessel: I think just answering the questions that you don't know. So like you said, medicine is science, but I think already as a child 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.

5:23Catherine Houlihan: All right, let's get to the outbreak now. Catherine, if you could just give us an overview of what happened from the very beginning.

5:30Vincent Racaniello: 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, travelling towards Cape Verde through multiple islands and very early 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 and one of whom also dies but after being after coming off the boat another individual this case Case three becomes unwell after coming off the boat.

6:33Vincent Racaniello: But the boat continues to sail on. And at 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 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.

7:10Catherine Houlihan: I just looked it up this morning. The MV Hondias is on its way to Greenland on another cruise, so it's still in business. Yes. So we've had experiences with hantaviruses before. They're typically zoonotic infections, right? But they don't establish long change of infection with the exception of Andes, right?

7:32Vincent Racaniello: 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 transmission, and that's what's happened in this case.

7:46Catherine Houlihan: 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 where they got this exposure to the rice rat and Andy's virus. How certain are we about that? Is there any actual evidence for that?

8:05Corinne Guerts van Kessel: Yeah, so the information comes from their travel logs and 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. A 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 board 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?

8:47Corinne Guerts van Kessel: Yes, that's ongoing. That's currently ongoing. So Catherine, the two individuals presumably boarded during their incubation period, right?

8:59Catherine Houlihan: How long would you say they were incubating before the first symptoms, which are April 6th, right?

9:05Vincent Racaniello: 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 probably of boarding. The 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.

9:51Vincent Racaniello: If you count backwards, looking at where they have both acquired this infection, 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.

10:14Corinne Guerts van Kessel: 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 travelled in a camper, so they visited several areas.

10:26Catherine Houlihan: But it seems that it's really hard to know if she didn't get infected herself on land because the incubation period is so long, right?

10:36Vincent Racaniello: Can be up to 42 days, yeah, but it is usually shorter than that. 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. And 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.

11:32Catherine Houlihan: So we do have samples from her. Were they sequenced?

11:37Vincent Racaniello: Yes, they have been sequenced, yes. So we know that was an Andes virus.

11:40Catherine Houlihan: Okay, so then we have to match them to the rodent isolates if we ever get them, right? Yes, definitely. So 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.

12:01Vincent Racaniello: 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. and 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.

12:44Vincent Racaniello: A really nicely designed study that gave us the kind of information that people are viremic before they're symptomatic from 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.

13:07Catherine Houlihan: So to put together the pathogenesis, this is an inhaled pathogen from rodent excreta.

13:14Vincent Racaniello: Yes.

13:15Catherine Houlihan: Presumably it reproduces locally in the lungs and then establishes a viremic phase.

13:19Vincent Racaniello: Yes.

13:20Catherine Houlihan: Does it go to other, any tissues to reproduce? Do we know?

13:23Vincent Racaniello: It's replicating in lymphoid tissues, I think. Yeah, and then causing this disseminated viremia, particularly located in throats and salivary glands.

13:34Catherine Houlihan: And that's how it's transmitted to others?

13:36Vincent Racaniello: 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. And even, interestingly, again, leaning on data from Chile, transmission from a mother to a 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.

14:10Vincent Racaniello: We detect it in cravicular fluids. and nose and throat swabs. So the virus is there.

14:15Catherine Houlihan: There was a birthday party in Argentina, right, where people presumably transmitted it through droplets or aerosols, whatever, right?

14:24Vincent Racaniello: Yes, yeah.

14:26Catherine Houlihan: Corinne, so from the genomic evidence that we have, there's no more than one SNP difference per case. I don't know how many different evidences we have like that, but what would that mean?

14:41Corinne Guerts van Kessel: Yeah, so what we can learn from that is that the viruses are very similar between the different patients that we have detected. Yeah, 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 that there was another route of infection, unless, of course, there would have been rodents, for example, on board of the boat.

15:31But that has been, well, almost completely surely excluded.

15:37Catherine Houlihan: From how many patients do we have sequencing, do you know?

15:44Corinne Guerts van Kessel: I think we have them of almost, well, I can't say the exact number, but almost all the patients where we have done PCR confirmation. So that's, I think, 12 out of 13 because the index case didn't have material. So, yeah.

16:01Catherine Houlihan: So, 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?

16:17Vincent Racaniello: Yes. 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. So rats are now unable to sort of ferry up and down these ropes. 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 was actually an inspection in 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 of that.

16:52Vincent Racaniello: So their ports are very invested in making sure these ships, which bring people and pathogens to their shores when they have their distant islands, they invest quite a lot in safety and protection of ships. So 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.

17:23Corinne Guerts van Kessel: 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, and 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 viral genome in the rooms of the people that were actually ill. But there's no evidence up to present that there were any rodents on board that have...

18:02Catherine Houlihan: So there were genomes in the sick people's room, but not other rooms.

18:08Corinne Guerts van Kessel: 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.

18:19Catherine Houlihan: By 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 spill over 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?

18:49Corinne Guerts van Kessel: To be honest, I think it was just very unfortunate because I think the spillover from animal to human 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. You spend a lot of time together usually. And yeah, I think it's just very unfortunate that these people traveled and entered the boat.

19:36Catherine Houlihan: Do you think it had anything to do with their age and 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?

19:50Corinne Guerts van Kessel: 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 the spillover, I think. and that's also what we see in the different patients that got infected. 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 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.

20:26Catherine Houlihan: So Catherine, this ship had one doctor, There are 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.

20:59Vincent Racaniello: Yes, 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 uh this is a bit too early and maybe maybe the lessons here are that if you're on it if you're on a cruise if you're in an enclosed space uh and you start to feel unwell that's the time to maybe isolate because if this was any of the pathogens that we that were sort of would have been suspected like influenza and COVID, then you would ideally isolate and not pass it on.

21:49Vincent Racaniello: But I think we just don't as humans. We were sociable animals, aren't we?

21:53Catherine Houlihan: 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 proper hospitals, Maybe their lives would have been saved by being intubated and therapies and so forth. You can't do much in a cruise ship.

22:16Vincent Racaniello: And I think that's the thing that was difficult, is that the cardiopulmonary syndrome of Andesan 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.

22:33Catherine Houlihan: I remember the first outbreak of Sin Nombre in the U.S. 1993, I think, a 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?

22:56Vincent Racaniello: Fairly early. So the UK has these UK overseas territories. And so it was a Dutch ship. But I think the... Actually, we have to give a bit of credit to one of the doctors on the Ascension. island who flagged that as he was um assisting uh um the disembarked case the the case number three um who then was flown to johannesburg in an emergency uh repatriation well an emergency transfer to a to a high level center and then said i i think this uh 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.

23:34Vincent Racaniello: 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. So got everybody together and said, we've got this cluster. And that's when UK HSA started to get involved.

23:53Catherine Houlihan: What was the date on that one?

23:54Vincent Racaniello: That would have been in May, early May. Okay.

23:58Catherine Houlihan: And what about you? When did you get involved?

24:00Corinne Guerts van Kessel: 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 there'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.

24:46Catherine Houlihan: The crew was also Dutch, right? The whole crew?

24:49Corinne Guerts van Kessel: Not the whole crew because there were a lot of Asian crew members, actually from the Philippines. But I think, yeah, there were a lot of Dutch tour guides and people involved in the organization.

25:01Catherine Houlihan: Were there UK nationals on the boat?

25:03Vincent Racaniello: Yes.

25:04Catherine Houlihan: 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?

25:22Vincent Racaniello: It's because, I mean, I think a death on a cruise ship isn't terribly unusual. I 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.

26:02Vincent Racaniello: And then she actually passed away in Johannesburg. So 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.

26:28Catherine Houlihan: So the ship is making multiple stops after it leaves. It goes to South Georgia, Tristan da Cunha, St. Helena, Ascension, as you mentioned. Did any of them notice anything going on? I guess Ascension you said already, but any of the others?

26:43Vincent Racaniello: Yeah, I don't think so at that point because it's St. Helena and Extension Islands where these individuals had disembarked and well initially.

26:57Catherine Houlihan: Right. So the index dies on board April 11, correct?

27:02Vincent Racaniello: Yeah.

27:03Catherine Houlihan: Do you know what were the differentials at that point? Do we know?

27:08Vincent Racaniello: Yeah, I mean, presumably the doctor is thinking, like you mentioned, bird flu, we're in contact with a lot of animals. 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, Legionella, mycoplasma, severe strep pneumonia could kill people of that age. It 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.

27:50Vincent Racaniello: You have limited facilities to do any kind of diagnostics.

27:54Catherine Houlihan: And don't forget VirusX.

27:57Vincent Racaniello: VirusX.

27:58Catherine Houlihan: A new one, right, that we haven't seen before. 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?

28:13Corinne Guerts van Kessel: So I think the first laboratory testing was done on the patient that was transferred to South Africa. And they, of course, did their panel of respiratory viruses. So it was PCR testing. And, of course, the broader diagnostics. But in the end, the Hanta virus was detected by a PCR. And of course, then subsequently, they had to do rapid sequencing to identify the exact strain. But with a patient with this kind of symptoms coming from South America, I think the clue was quickly towards Andes virus. And it's good to mention that Institut Pasteur in Dakar, they were actually the lab that has confirmed the second and the third case.

28:59Corinne Guerts van Kessel: if I'm correct, but they were involved very rapidly as well.

29:03Catherine Houlihan: 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.

29:15Corinne Guerts van Kessel: The Hantavirus is not usually in the respiratory panels, so you have to specifically think of that. But I think it was mentioned in this consultation, so 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 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.

29:55Corinne Guerts van Kessel: So I think in the end it was done really efficient and in a collaborative way between all the different reference labs.

30:01Catherine Houlihan: And so there's a Hantavirus PCR primer set which will work for the various Hantavirus that we know of, correct?

30:10Corinne Guerts van Kessel: Yeah, you have a Panhantavirus PCR and you have specific Andisvirus PCRs as well. So once we knew that it was a Andisvirus, people started using the specific PCR.

30:21Catherine Houlihan: It's interesting that they suspected it because of the origin of the cruise, right? Is that what you said?

30:27Corinne Guerts van Kessel: Well, 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 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.

31:00Catherine Houlihan: I mean, that's the key. It's so rare, but still you have to keep it in the back of your mind, right?

31:07Corinne Guerts van Kessel: 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 I think that this one really shows that you have to combine different expertise and people to do this.

31:29Catherine Houlihan: So sometimes when you hear hoofbeats, you have to think of zebras. Yeah, I think so. I mean, they say, you know, just think of horses. Don't get too crazy, but sometimes you do.

31:39Corinne Guerts van Kessel: Yeah, or the unknown, right? It's also important that you said that it might be something we don't know.

31:44Catherine Houlihan: I think we answered this, but let me ask you anyway, Catherine, How was it then identified as Andy's?

31:50Vincent Racaniello: Yeah, I think it was then sequenced. 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. But 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 primer probes will pick it up.

32:25Catherine Houlihan: So, Corinne, is it safe to say that all the testing was done offshore, not on the ship?

32:30Corinne Guerts van Kessel: 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 Andesvirus rapid tests that could be done. Right. Go to the CVS and buy a Hantavirus rapid antigen test.

32:49Catherine Houlihan: Can't do it. Catherine, from the UK perspective, what were your key concerns?

32:58Vincent Racaniello: I think with this particular virus, it has a long incubation period. 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, which we can now all point to on a map, but previously would have struggled.

33:36Vincent Racaniello: 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 been 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.

34:05Catherine Houlihan: So 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?

34:14Vincent Racaniello: Yes. Yeah, you can't. I mean, we can't really stop people continuing until you know there's Hunter. And then even then, stopping people from continuing their lives as they wish is, you know, really challenging.

34:28Catherine Houlihan: Apparently not in the U.S. No comment.

34:36Catherine Houlihan: Corinne, from the Netherlands perspective, you have a Dutch ship with Dutch crew. What are you concerned about?

34:45Corinne Guerts van Kessel: Well, 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 partly came from Asia. Yeah, they had to be quarantined in the Netherlands because it was part of the Dutch responsibility. So this quarantine thing was complex, but I think very well and structured done. And I think everyone really accepted their quarantine and everything.

35:24Corinne Guerts van Kessel: 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. So 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.

36:12Catherine Houlihan: So, 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?

36:27Vincent Racaniello: 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. So Tenerife made sense. It has high-level medical facilities in addition for anyone becoming unwell.

36:46Catherine Houlihan: So tell us about your experience. They sent you there by yourself, right? So what did you do?

36:53Vincent Racaniello: 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. And 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.

37:43Vincent Racaniello: 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. And 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.

38:22Vincent Racaniello: My plan getting on the plane had been to train one of the aircrew. The aircrew were absolutely brilliant and they obviously deal with quite a lot of infections through aircrew because people often get on well 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.

38:42Catherine Houlihan: Well, you obviously did it right because you didn't get sick, right?

38:46Vincent Racaniello: 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.

38:53Catherine Houlihan: So looking back, is there anything you would have done differently?

38:57Vincent Racaniello: I 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. 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 become symptomatic, I'm going to want to know where they sat. So after they'd sat down and we'd all sort of got ready, I then decided to make a list of and make and draw a map and all this kind of stuff.

39:35Vincent Racaniello: 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 will use the back toilet. All of these things.

39:52Catherine Houlihan: Well, they picked the right person, right?

39:56Vincent Racaniello: I mean, we didn't have to test it.

39:59Catherine Houlihan: So Corinne, when the evacuation happens in the Netherlands, What are the patients like? Are they very sick?

40:08Corinne Guerts van Kessel: So 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. And 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.

40:53Corinne Guerts van Kessel: But that did not happen.

40:55Catherine Houlihan: So given that there's a long incubation period, right, were you confident that you could keep track of these patients?

41:02Corinne Guerts van Kessel: um well i think we were quite sure that with the the 42 days we were at the safe side and and following up i mean it was quite shocking of course when one of the so in the netflix we had one of the patients that was in the follow-up that turned that tested positive so we did feel like okay we're doing the right thing because we're we're testing them on a weekly base and so the patient developed symptoms when we already knew that he was positive. So we felt that we were doing the right thing. And yeah, I think with the period that we took, 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,

41:46Catherine Houlihan: one to eight weeks. Do you have any sense for why it would have such a broad range?

41:52Corinne Guerts van Kessel: 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. So 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.

42:39Corinne Guerts van Kessel: So there's still quite some questions to answer there. Any thoughts on that, Catherine?

42:43Vincent Racaniello: Yeah, I agree. It's an area for development. and it's in the list of questions that we wish we understood better. I 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 discussions we've had actually with a Chilean professor, Pablo Vial 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 it's more a functional disorder that it causes in the epithelial lining and hence the cardiopulmonary syndrome happens because the membranes become leaky rather than it causing a lytic infection so I think it's the the danger of the immune system later on rather than, um, rather than the virus itself.

43:41Vincent Racaniello: I think we tolerate the virus until, until we don't.

43:45Catherine Houlihan: So talk, talk about the lab results as you saw them come in. Were there any surprises?

43:51Vincent Racaniello: I mean, from the UK point of view, we actually, I mean, we repatriated, we had 85 high risk contacts scattered around, but we, um, we had 35 individuals in our Arrow Park isolation, um, because they weren't, 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. So we think we've got them out.

44:26Vincent Racaniello: 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. So really interesting comparative public health virology there, which is really interesting.

45:03Vincent Racaniello: But there is one other really interesting result, which is from an individual who doesn't currently count as a case that I'm really interested in Corine's thoughts on, who is the healthcare worker who had a transient viremia but did not zero convert. And I wanted to grill you about your laboratory results from that.

45:21Corinne Guerts van Kessel: Yeah, so in the Netherlands we have done testing and we have a combined reference lab at Erasmus MC and the National Institute of Health. And 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. So there's always a bit of discussion about sensitivity of the assays.

46:07Corinne Guerts van Kessel: 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 varemia.

46:36Catherine Houlihan: So 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?

46:51Corinne Guerts van Kessel: I 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.

47:18Catherine Houlihan: So Catherine, you said earlier that you were in contact with some Argentine scientists because they've had experience. What did you learn that was useful?

47:27Vincent Racaniello: Well, first of all, there was a lot of offering of sharing of lab reagents and lab protocols and ELISA plates and really amazing offers of support to the countries affected. So really nice offers from Chile and Argentinian 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. They didn't see them making a difference to the viral load during illness.

48:07Vincent Racaniello: It was more, you know, a catabant as a sort of immunotherapy specific to the pathophysiology of the virus, but some really useful thoughts throughout the whole event.

48:23Catherine Houlihan: International cooperation. It's good.

48:25Vincent Racaniello: Beautiful.

48:26Catherine Houlihan: Corinne, if there were tomorrow another pathogen outbreak on a cruise ship and you got involved, would you do anything different?

48:38Wow

48:39Corinne Guerts van Kessel: I think we did quite a good job I think from the outside it's always easy to comment on things that we should have done differently but 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. But it's really hard if you're on this ship, obviously, to make these decisions also for the clinicians that are on board.

49:22Corinne Guerts van Kessel: So I think it was all, there was a lot of things that went well.

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

49:34Vincent Racaniello: I 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, if 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.

50:16Vincent Racaniello: But equally, I mean, they always have problems. The Diamond Princess had problems with COVID. And you've mentioned Norovirus is the primary reason.

50:24Corinne Guerts van Kessel: 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, including the information they give 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 the previous months?

51:05Corinne Guerts van Kessel: Yeah, I think a lot of these kind of cruises, they attract people that, of course, like nature, that 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.

51:29Catherine Houlihan: 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?

51:39Vincent Racaniello: I mean, yes, they have been made. I think particularly the Andes monoclonal has got some hamster model evidence, doesn't it? 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, so for Andes. And so I think that wasn't the choice we made.

52:16Vincent Racaniello: 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? Monoclonals versus antivirals. What should we be using in post-exposure prophylaxis? And it's the question that comes up for all of these emerging infections, including Bundabugu, what have we got for post-exposure prophylaxis?

52:53Vincent Racaniello: Not very much. And that's where I think we need to start thinking more, carrying out more research in that area.

53:02Catherine Houlihan: Corinne, what one uncertainty about this outbreak would you like to see resolved?

53:09Corinne Guerts van Kessel: Yeah, 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 hantiviruses. 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. So that's my personal interest.

53:46Catherine Houlihan: Catherine, this outbreak got a lot of international attention. Why is that?

53:52Vincent Racaniello: Yes, it did, didn't it? And I think it's because it reads like a horror story almost. It reads like a 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 people traveling on a cruise ship is interesting press. But 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.

54:34Catherine Houlihan: Irene, what would you have done if you hadn't become a scientist?

54:40Corinne Guerts van Kessel: I think I would have become a journalist, actually. Cool.

54:45Catherine Houlihan: You may have covered this outbreak. Who knows? How about you, Catherine?

54:50Vincent Racaniello: Yeah, that's a good one. Investigative kind of journalist or detective. Solving crimes. You could do the same thing? Solving puzzles.

54:58Catherine Houlihan: You would do the same thing?

54:59Vincent Racaniello: I'd go detective. I'd go solving crime.

55:03Catherine Houlihan: Well, you could work together.

55:05Corinne Guerts van Kessel: We can continue.

55:07Catherine Houlihan: And you could have a nice TV show about it. I think those exist. All right, that's a special episode of TWIV from ESCV 2026. You can find the show notes at microbe.tv. If you enjoy our science programs, we'd love your support. You can go to microbe.tv. My guest today from University College London and UK HSA, Catherine Houlihan. Thank you so much.

55:36Vincent Racaniello: Thank you.

55:43Catherine Houlihan: And from Erasmus Medical Center, Corinne Goertz van Kessel. Thank you so much.

55:53Catherine Houlihan: 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 for 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.