On May 3, the World Health Organisation (WHO) announced the death of three passengers on the MV Hondius, a cruise ship crossing the Atlantic Ocean, from hantavirus. Measures were quickly taken to quarantine and keep under close surveillance those ill or possibly infected with the virus, which has a 38 percent lethality rate, according to the US Centres for Disease Control and Prevention (CDC). Contact tracing also began in an attempt to track down people who might have been infected.
However, some social media users were quick to say that these health measures weren’t justified because, according to them, hantavirus can’t be spread from human to human.
X users claimed that in the early 1990s, hantavirus wasn’t considered contagious. They’ve been sharing as “proof” a document labelled “Hantavirus Fact Sheet”, attributed to the San Juan Basin Health Department in Colorado in the United States. The Fact Sheet does say that the virus can’t be passed from person to person.
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However, contrary to the claims made by these social media users, the strain of hantavirus identified on the MV Hondius can be spread from person to person.
A different virus species
The San Juan Basin Health Department is a real health department that existed at one time in Colorado, though it was dissolved on January 1, 2024. That makes it difficult to establish if the document that is circulating online about hantavirus is authentic or not.
Our team used the Wayback Machine – a site that archives websites – to search for pages of the San Juan Health Department’s website that might contain the word "hantavirus" in their address. We found a document of tips to prevent the spread of hantavirus that was published in 2001. This document has the same claim that appears on the fact sheet that’s been circulating online: that the virus is “not contagious” and can’t be spread from person to person.
Our team contacted the La Plata County Health Department, which took over after the San Juan Basin Health Department shut its doors. People there said that the fact sheet shared online “seemed authentic” but were unable to say with one hundred percent certainty.
However, that is still not proof for the claims that social media users have been making: that the virus detected on board the MV Hondius can’t be transmitted from person to person.
The La Plata County Public Health Department confirmed that hantavirus has indeed been present in Colorado since 1993. However, they specified that the strain present in Colorado is the Sin Nombre virus, a totally different species from the Andes hantavirus strain found on the MV Hondius.
The doctors who spoke to our team confirmed that these two strains of virus are very different.
"It’s not at all the same virus,” said Mircea Sofonea, an epidemiologist at Montpellier University and the Nîmes University Hospital.
"It’s kind of like cars,” said Bruno Lina, chief of the virology department at Hospices civils de Lyon, Lyon’s university hospital. “You have the make and then the models: you have the Andes virus, the Jura virus and the virus in Colorado. These are all different viruses.”
Documented person-to-person transmission with the Andes hantavirus
While the Sin nombre virus, like most hantaviruses, can’t be spread between humans, that isn’t the case for the Andes virus.
"The Andes virus is the only one in this grouping that has established human-to-human transmission,” says Sofonea.
Contrary to the claims circulating online that hantavirus can’t be spread between humans, human-to-human transmission has been documented by scientists, notably in a study published by The New England Journal of Medicine about an outbreak in Argentina in 2019. The La Plata County Public Health Department also confirmed to us that the Andes virus can be spread between humans.
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However, this hantavirus isn’t actually very contagious at all, says Lina. Only a “relatively prolonged” contact with an infected person could lead to transmission of the virus, Sofonea says.
While we still don’t have all of the epidemiologic data, hantavirus’s R0 – a mathematical term that indicates a virus's contagiosity – is “only around 1,” Lina says. In comparison, during the 2020 pandemic, Covid’s R0 was around 3.28, which indicates that one infected person would, on average, infect three others.
"If a person was infected by Covid on the MV Hondius, which had 150 passengers, then we would have ended up having about 60 cases. But with hantavirus, the number was much smaller than that,” Lina says. For the time being, there have been only 12 suspected and confirmed cases in total.
"With a few preventative measures and good hygiene, we can make the R0 drop below 1 and, at that point, the epidemic will be over,” Lina added.
This article has been translated from the original in French by Brenna Daldorph.
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