Hantavirus has been confirmed in a French citizen evacuated from the MV Hondius cruise ship on Sunday, while two tests on a  US citizen turned up one “weakly positive” and one negative result – but it is still unclear how the virus is being transmitted.

The evacuation of passengers from the ship, now docked in Tenerife in the Canary Islands, continued on Monday under the supervision of health officials from Spain, assisted by the World Health Organization (WHO) and several other European countries. Passengers were only allowed to disembark to board chartered flights arranged by their countries.

However, countries differ on how they plan to treat citizens who do not test positive for the virus right away, given that it can take up to 42 days before symptoms appear.

Quarantine

Spain, the UK, and Australia will require citizens to quarantine in designated government facilities for varying periods.

The six Australians will spend up to 42 days in a government quarantine facility while undergoing PCR testing, according to Health Minister Mark Butler.

US health officials – many vehemently against lockdown measures to contain COVID-19 – have suggested that asymptomatic citizens will be allowed to return home.

Sixteen of the 18 US evacuated passengers are currently being assessed in a regional emerging special pathogen (RESPTC) treatment centre in Omaha, Nebraska. Two others, including the person with the weakly positive test, are being assessed in Atlanta. 

John Knox, deputy secretary for Strategic Preparedness and Response at the Department of Health and Human Services (HHS), told a media briefing on Monday afternoon that asymptomatic passengers may be able to complete 42 days of isolation at home if they remain without symptoms and have the necessary support.

On Sunday, Dr Jay Bhattacharya, acting director of the US Centers for Disease Control and Prevention (CDC), told CNN that asymptomatic passengers could not spread the virus.

However, Nebraska Governor Jim Pillen told Monday’s media briefing that “no one who poses a risk to public health is walking out the front door”.

How close is ‘close contact’?

Although most transmission is from rats, human-to-human transmission of the Andes virus, the hantavirus species affecting the ship, has previously been documented in Argentina in 2018. 

Genome sequencing of the current outbreak has shown it to be 99% similar to that outbreak, where the index patient attended a concert, subsequently infecting 34 people.

BREAKING: First sequencing of the Hantavirus from the outbreak.

-99% identical to a June 2018 case from a patient in Argentina
-10.4 SNV/year mutation rate
– The Andes genome is about 12 kb across three RNA segments. At 10⁻⁴ to 10⁻³ substitutions/site/year, that translates… pic.twitter.com/FleaIMmORV

— Dr Steven Quay (@quay_dr) May 11, 2026

Human-to-human transmission is possible with “close contact”, according to the World Health Organization (WHO). 

However, there is some debate about the nature of this “close contact”. Professor Joseph Allen from Harvard’s Department of Exposure Assessment Science, said in a weekend TV interview that a doctor on board the ship had told him that some infected passengers had little interaction with the first three patients identified with the virus. These are a Dutch couple (now deceased), and a British man, currently making a slow recovery in South Africa.

The International Hantavirus Society and members of the international hantavirus research and clinical community have also warned against various “simplified conclusions”, including that the Andes virus (ANDV) has “minimal or negligible human-to-human transmission potential” and that only symptomatic patients are infectious.

Are asymptomatic people infectious?

The experts warned in a statement last week that “the precise timing of infectiousness remains incompletely defined”. 

“While symptomatic patients are likely to represent the highest-risk group, available outbreak reconstructions do not support overly categorical statements that transmission can occur only after clear symptom onset,” they said. 

“Transmission potential during prodromal, early symptomatic or minimally symptomatic phases, should be considered when designing contact tracing, testing and quarantine strategies.”

They stated that this is “particularly relevant in closed settings such as a cruise vessel where ANDV-exposed individuals may still be within the incubation period”.

Infectious disease specialist Dr Jeremy Faust, writing in his substack, on Monday said that “it remains possible that an animal on the ship spread [Andes virus] to multiple people, or that the infected people visited the same place on land where the virus was waiting for them”.

But, Faustus added, “given that human-to-human superspreader events of the Andes hantavirus have been documented, I’d bet that human-to-human transmission did occur here”, adding that the ship’s doctor also got infected.