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At Least One Evacuated American Passenger From m/v Hondius Tests Positive for Hantavirus
#19,156
Overnight the HHS announced that - of the 17 evacuated Americans from the m/v Hondius - 1 (currently asymptomatic) individual has tested positive for Hantavirus, and a second individual has shown `mild symptoms'.
While the mantra has been that testing of asymptomatic individuals was unlikely to yield positive results, this is a reminder that there are very few absolutes when it comes to viruses and human physiology.
We discussed the possibility of asymptomatic spread of the Andes Virus a week ago, and while evidence is sparse, studies have suggested (see Serological Evidence of Hantavirus Infection in Apparently Healthy People from Rural and Slum Communities in Southern Chile) that at least some infections may be mild or asymptomatic.
A more recent 2025 study (see Virological characterization of a new isolated strain of Andes virus . . .), published in PloS NTD reported:
In this work, we described the isolation of the strain responsible for the largest ANDV PTP transmission outbreak, which occurred in the small town of Epuyén and began on November 2, 2018. This strain, ARG-Epuyén, exhibited a high capacity for PTP transmission, necessitating the implementation of quarantine measures to curtail further spread [8].
The median reproductive number (the mean number of secondary cases caused by an infected person) was 2.12 before control measures were implemented and subsequently dropped to below 1.0 by late January.
Early intervention allowed for the collection of samples leading to the isolation of this new ANDV strain from an asymptomatic case. An early passage of this strain was sequenced, revealing only one amino acid difference from the virus recovered from the patient. Like the Andes/ARG strain, this strain was able to grow in a new host without needing adaptation [26].
So while rare, there is precedent for positive test results from asymptomatic individuals.
What isn't well understood is whether - or how effectively - asymptomatic (or presymptomatic) individuals may be able to transmit the virus. The ECDC's Threat Assessment Brief, published on May 6th, had this to say:
While a lot of governments, eager to reassure the public, are quick to equate asymptomatic with `healthy', the reality is far more nuanced. Given its lengthy incubation period, an exposed individual's status can change in a matter of hours.
Which is why - while not wanting to use the dreaded `Q' word - exposed individuals around the world are being segregated and monitored for symptoms.
While I remain far from convinced that this Andes virus outbreak will turn into a global public health emergency, there are enough unknowns here to command our respect and attention.
And even if the current strain of ANDV is incapable of bigger things, evolution is a thing.
Meaning that anything we say today about the virus may not hold true tomorrow.
#19,156
Overnight the HHS announced that - of the 17 evacuated Americans from the m/v Hondius - 1 (currently asymptomatic) individual has tested positive for Hantavirus, and a second individual has shown `mild symptoms'.
While the mantra has been that testing of asymptomatic individuals was unlikely to yield positive results, this is a reminder that there are very few absolutes when it comes to viruses and human physiology.
We discussed the possibility of asymptomatic spread of the Andes Virus a week ago, and while evidence is sparse, studies have suggested (see Serological Evidence of Hantavirus Infection in Apparently Healthy People from Rural and Slum Communities in Southern Chile) that at least some infections may be mild or asymptomatic.
A more recent 2025 study (see Virological characterization of a new isolated strain of Andes virus . . .), published in PloS NTD reported:
In this work, we described the isolation of the strain responsible for the largest ANDV PTP transmission outbreak, which occurred in the small town of Epuyén and began on November 2, 2018. This strain, ARG-Epuyén, exhibited a high capacity for PTP transmission, necessitating the implementation of quarantine measures to curtail further spread [8].
The median reproductive number (the mean number of secondary cases caused by an infected person) was 2.12 before control measures were implemented and subsequently dropped to below 1.0 by late January.
Early intervention allowed for the collection of samples leading to the isolation of this new ANDV strain from an asymptomatic case. An early passage of this strain was sequenced, revealing only one amino acid difference from the virus recovered from the patient. Like the Andes/ARG strain, this strain was able to grow in a new host without needing adaptation [26].
So while rare, there is precedent for positive test results from asymptomatic individuals.
What isn't well understood is whether - or how effectively - asymptomatic (or presymptomatic) individuals may be able to transmit the virus. The ECDC's Threat Assessment Brief, published on May 6th, had this to say:
Do asymptomatic individuals have a role in transmission?
Current very limited evidence does not support a significant role for asymptomatic individuals in hantavirus transmission, supporting active symptom monitoring of asymptomatic exposed individuals. Infectivity is highest on the first day of symptom onset, which indicates a high likelihood of some infectiousness one-two days before onset of symptoms.
Current very limited evidence does not support a significant role for asymptomatic individuals in hantavirus transmission, supporting active symptom monitoring of asymptomatic exposed individuals. Infectivity is highest on the first day of symptom onset, which indicates a high likelihood of some infectiousness one-two days before onset of symptoms.
While a lot of governments, eager to reassure the public, are quick to equate asymptomatic with `healthy', the reality is far more nuanced. Given its lengthy incubation period, an exposed individual's status can change in a matter of hours.
Which is why - while not wanting to use the dreaded `Q' word - exposed individuals around the world are being segregated and monitored for symptoms.
While I remain far from convinced that this Andes virus outbreak will turn into a global public health emergency, there are enough unknowns here to command our respect and attention.
And even if the current strain of ANDV is incapable of bigger things, evolution is a thing.
Meaning that anything we say today about the virus may not hold true tomorrow.
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