How long should Hantavirus cruise ship passengers self-isolate? And why does B.C. recommend less time than WHO?

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The other thing that has not been reported very much publicly is a mapping of the relationships and contacts amongst passenger on board who did become ill.

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Transmission of the Andes strain of hantavirus is not thought to be particularly efficient, in the way that we get very efficient airborne transmission of things like measles or COVID-19 or influenza. It’s really thought to require more sustained close contact.

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And so that also has to layer onto risk assessment. Determining quarantine period is probably driven, at least to a certain extent, by whether the individuals who are not experiencing signs and symptoms had any degree of sustained or close contact with the people who did experience symptoms.

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I think what’s reassuring by the statement put out by British Columbia is that they are saying a minimum of 21 days, which I think leaves the door open to extending that as more information becomes available.

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I would expect that these individuals will be tested frequently to determine where or not their is an active infection happening.

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But isn’t any kind of contact, on a relatively small ship, close contact?

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If we’re talking about a virus like measles that is extraordinarily contagious in normal settings, one person might infect 12 to 15 other people. The data to date suggest the Andes virus requires sustained close contact, and not just close, like adjacent room. Close, physical contact.

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There have (historically) been relatively few human cases of this virus and even fewer where the evidence has been for human-to-human transmission, rather than rodent-to-human transmission. There are a lot of questions about how efficient is airborne contact versus contact that actually requires direct exposure to bodily fluids or contaminated surfaces, for example.

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Do we know what the reproductive number is for the Andes strain  — how many people each infected person can go on to infect?

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Based on previous outbreaks, it seems to be the case that, at a maximum, it’s one to two and, in many cases, it’s lower than one which is why these infections have fizzled out. As soon as the (reproductive number) sinks below one, an outbreak can’t sustain itself anymore.

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Port vessels accompany the MV Hondius as it departs the Granadilla Port after all passengers were evacuated on May 11, 2026 in Tenerife, part of the Canary Islands, Spain. Photo by Chris McGrath /Getty Images

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What’s the distinction between quarantine and self-isolation?

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In the most extreme forms of quarantine you might be in something like an isolation unit at a hospital or in some sort of health-care facility. Individuals would have to enter your room in personal protective equipment — gowns, masks. For nasty viruses like Ebola people might even wear suits that have dedicated air flow. That’s an extreme form of quarantine for viruses that are known to be both highly contagious and high virulent (meaning) of high consequence, likely to induce severe disease.

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Self-isolation at home is obviously more appropriate for individuals who are at inherently lower risk and for pathogens that have inherently more limited ability to transmit.

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What do we know about human behaviour in disease outbreaks? Do people abide by rules for self-isolation?

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That’s a really good question. I don’t know, is the honest answer. But I think it also depends on the situation and perception of risk.

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Early on in the COVID pandemic, there was a lot more adherence to isolation guidance than later, when people’s perception of risk changed based on their experience and a better understanding of who is at risk of getting severe infections.

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I think, anecdotally, in situations where there is something particularly exotic and there are a lot more unknowns that adherence tends to be stronger than in situations where it’s a pathogen or a situation we might be more familiar with.

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You mentioned that infections appear to be fizzling out, but it was reported Monday that a woman in France who was evacuated from the ship on Sunday tested positive for hantavirus and that her condition deteriorated quickly. What should we take from that?

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It underscores that there are a lot of unanswered questions. This is not a virus that is super well studied and it’s not a virus that we have a huge degree of experience with, in terms of human infections and human transmission.