Hantavirus cruise ship outbreak explained

Interview with Mark Fielder, Kingston University

Part of the show Hantavirus outbreak, and salmon on cocaine

The MV Hondius - which left Argentina at the beginning of April - has been dealing with an outbreak of a hantavirus - specifically the Andes strain of the virus. Several of the ship’s passengers have been infected, with fatalities reported. Others are now self-isolating at home. It’s unclear how the outbreak began, or whether person-to-person transmission of the virus - which has been claimed in previous outbreaks but is nevertheless extremely rare - is behind at least some of the cases. The World Health Organization has been leading the response, and their chief, Tedros Adhanom Ghebreyesus, had this to say at a press conference on the 7th of May, 2026…

Ghebreyesus: Eight cases have been reported, including three deaths. Five of the eight cases have been confirmed as hantavirus, and the other three are suspected. Hantaviruses are a group of viruses carried by rodents that can cause severe disease in humans. People are usually infected through contact with infected rodents, or their urine droppings, or saliva. The species of hantavirus involved in this case is the Andes virus, which is found in Latin America and is the only species known to be capable of limited transmission between humans. 

WHO chief, Tedros Adhanom Ghebreyesus. Mark Fielder - a professor of medical microbiology at Kingston University - has been telling Chris Smith more about hantavirus infections…

Mark - These are an interesting group of viruses that emerged basically out of rats, and mice, and rodents, and that's where we commonly see them existing, and that's where we get the transmission to humans if we get that transmission from. There are two sets of viruses really; there's what we call the Old World viruses, which are the ones that exist in Europe and across Asia, and the New World viruses, which are the ones that occur in places like Argentina, and Chile, and Brazil. They both present with similar diseases, you get the flu-like illness which can then develop in different ways depending on whether you've got the Old World strain or the New World strain, and the Old World strain tends to give you sort of renal problems, gastrointestinal problems as does the New World strain, but it sort of pretty much ends there and it can be fatal, it can give about 10 to 15 percent fatality rate, whereas the New World viruses are a little different, they can actually develop into a much more hemorrhagic fever, and cause more problems, and fatality rate there can be up to 20 to 40 percent, depending on the patient and the circumstances. So they're quite a diverse group of viruses, but the one we're looking at at the moment appears to be a strain called the Andes strain of hantavirus, and that's one of the New World viruses, unfortunately, and it looks like it might have been picked up in and around the area of Argentina.

Chris - How does it spread normally if it's in these small animals like rats, and mice, and so on, small rodents? How do people get it?

Mark - Urine or faeces from rodents, and that might be direct contact or it might be in areas perhaps in barns or sheds, something like that, where rats or mice have been, and have urinated, and defecated, and people are sweeping up and the dust that's formed carries the virus, so that's one way it could get in. It also, in rare cases, can get into a patient via a bite from a rodent. There have been cases where salivary transfer have got into a patient, but that's rare because rodent bites are a lot rarer. In some cases, we have had human-to-human contact and transmission. When it occurs, it is a rare event, but when it occurs, it's because patients have had very close, and possibly intimate contact, so we're talking about people sharing a very close space together, perhaps kissing, lying close together and breathing so that one inhales the other's breath so as to speak. So there's a number of different ways, but principally for the rats and the mice, it's via the urine in the faeces.

Chris - How does it actually cause disease? So once it goes in, you're saying it's usually breathed in, that's going to be a respiratory infection, so how does it cause disease, and how does it lead to a fatality when that happens?

Mark - It gets into the lungs and starts causing damage in the lungs, which causes the lungs to be leaky, and fluid can enter the lungs and cause effectively something like a pneumonia, and that damage and fluid in the lungs starts to limit your ability to breathe. It can also cause gastrointestinal distress, so patients get an upset stomach and diarrhoea, and with all the immune response that's going on, you get myalgia, muscle aches and pains, and you get great fatigue, great tiredness. So all these things brought together is not a great end point as far as the disease is concerned, or you getting the disease, and of course damage to your lungs is something the body takes great lengths to try and limit, and stop, and prevent because your lungs are vital to your survival, so it's that damage to your lungs, and ultimately once it's got through your body down to your kidneys, that can cause a real problem.

Chris - What are the possibilities then to explain how these people on this boat got this in the first place?

Mark - Yeah, this is a really interesting question, and it is the question of the day, quite frankly, because that's one of the things we don't yet fully know. We know that some of the patients have been touring around parts of Argentina. We know that several people on the boats have been to rural areas as part of their tour, so there's possibilities there that patients could have picked up some virus, perhaps becoming contact with urine and faeces from the rodents there, and there's been some suggestion that one of the couples have been looking at birds and doing some bird watching, and they went to a landfill site to see these particular birds that they were looking for, and, of course, we all know that rodents are very frequent around landfill sites so there may have been contact there, but at the moment that's speculation because we don't know. There's been some suggestion that it might have been rodents on the boat. The boat operators have said at the moment they don't recognise that there are any rodents on the boat. I would probably favour this is something that the patient's been environmentally exposed to, so they're on land somewhere and taking it onto the boat rather than the other way around, but at the moment, until a full investigation is done and the full epidemiological studies are done, we're not entirely sure.

Chris - How then will they disentangle a source that was ashore or on the boat from some cases arising because someone else on the boat, who's already got it, perhaps they got it from the shore, or the boat, gave it to another person, because all of these things could be happening.

Mark - Absolutely, and this is one of the things the epidemiological studies will start to untangle or try to untangle. They'll be interviewing the patients and people on board that they can to try and understand where they've been, what was their footfall before they got onto the boat, and then who have they interacted with, if they can remember and if that is feasible, whilst they've been on the boat. So have a couple or a group of people been walking around a waste site looking for particular birds or have they not, and if they've not, and they only remained in very urban areas where perhaps the chances of coming across faeces and urine from rodents is much less, then it'll start to skew the epidemiological view about where they might have picked things up. Then, if they come onto the boat and there's one person with a very low-risk background and one with a higher-risk background, and they spent a lot of time together, and one couple has got the infection from the other, then they can start to see a pattern and a line where we might see a development of the disease via one particular route of infection rather than another. But at the moment, that epidemiological study will be very much underway with all the patients that they can talk to.

Chris - How should they manage this then? Because, to my mind, they've got a boat with 150 people on it, they've had a handful of cases of a disease that might or might not be transmitting person to person. What's the overall risk that's posed, and what should they do with all of these people on the boat who, at the moment, are perfectly well, but currently not allowed to go anywhere?

Mark - I would imagine probably the risk on the boat is moderate, and the reason I say that is because by definition, they can't go away. That doesn't mean that they are all sitting there cheek-to-cheek on that boat; they're not, of course, but there is closer contact than there would be if we could send people home. The chances of the virus spreading are a little higher on the boat than they are if they were off the boat, which I think one of the things they'll try and do now is get people disembarked when they possibly can. They'll do an assessment on their general health, and assuming that they are not currently showing symptoms or unwell, then those patients might well be, after a short period of time, sent back home. If they develop any symptoms, they'll probably be contacted daily and asked what symptoms they're showing, if they're showing any, and as soon as they're showing any minor symptom, they will be taken under medical care and isolated very quickly. But I think that's probably the risk level is moderate on the boat, and once the patients leave the boat and assuming they're all healthy and all the health checks are done, I think our onward infection risk is very low.

Chris - And will they be followed up for the rest of the incubation period, which can be eight weeks, can't it, for these viruses? It can be a long time for some of them, so you might be looking at two months for someone to sweat, worrying that they might succumb to this.

Mark - I think that is likely. It's a necessary outcome. We need to make sure that these patients are safe, both from a public health point of view in terms of spreading the disease onwards and also for their own health.