Is Hantavirus Mutating To Become More Contagious? US Experts Say No

Health officials investigating the deadly hantavirus outbreak linked to the cruise ship MV Hondius say there is currently no evidence that the virus has mutated to become more contagious or severe. The reassurance comes after genomic sequencing of the virus showed it remains nearly identical to strains previously linked to outbreaks in South America, according to experts from the European Centre for Disease Prevention and Control (ECDC). The outbreak has so far been linked to 10 cases, including eight confirmed infections and three deaths.

The development also follows growing global concern over whether the virus may have adapted to spread more efficiently between humans after several infections were reported among passengers and crew aboard the ship. However, European and US experts say available evidence does not currently support fears of a major viral mutation.

According to Bloomberg, one American doctor initially treated as a possible hantavirus case in the United States later tested negative twice, further easing concerns about wider spread. Meanwhile, another isolated passenger in Italy also tested negative. Health agencies including the World Health Organization (WHO) and ECDC are continuing large-scale international contact tracing efforts while monitoring passengers across multiple countries.

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What Experts Are Saying About Mutation Concerns

Speaking during a European health briefing, Andreas Hoefer, a microbiology and molecular epidemiology expert with the ECDC, said sequencing analysis showed no meaningful genetic changes suggesting the virus had evolved to spread more aggressively.

"At the moment there is no data to suggest this virus is behaving any differently in transmissibility or severity," Hoefer said, according to Bloomberg. He added that all viral sequences studied so far were "virtually identical" to previously known South American hantavirus strains. The ECDC believes the initial passenger was likely infected in South America before boarding the MV Hondius cruise ship.

Scientists closely monitor viral mutations during outbreaks because genetic changes can sometimes increase transmissibility, disease severity or immune evasion. However, experts say no such pattern has yet emerged in this outbreak.

Can Hantavirus Spread Between Humans?

Hantaviruses are primarily rodent-borne viruses transmitted through contact with infected rodents, urine, saliva or droppings. According to the US Centers for Disease Control and Prevention (CDC), most hantavirus infections worldwide do not spread efficiently between humans. However, certain South American strains, particularly Andes virus, have previously shown limited human-to-human transmission under close-contact conditions. 

This possibility has made investigators particularly cautious during the MV Hondius outbreak. According to Bloomberg, ECDC officials said the virus may potentially be detectable in blood up to two days before symptoms appear. This has prompted authorities to expand contact tracing to include people exposed before symptom onset. Experts stress that this does not necessarily mean the virus has become airborne or highly contagious like influenza or Covid-19.

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US And European Cases Ease Some Fears

Some concerns surrounding international spread eased after several suspected cases outside the cruise ship outbreak tested negative. Bloomberg reported that Stephen Kornfeld, an oncologist from Oregon who helped care for ill passengers aboard the MV Hondius, initially tested "mildly positive" in the Netherlands but later tested negative twice. Kornfeld had reportedly stepped in to provide medical care after the ship's primary doctor became ill.

Separately, Italian health authorities confirmed that a 25-year-old man isolated after possible exposure also tested negative for hantavirus. However, a former passenger in France remains critically ill in intensive care and is receiving extracorporeal membrane oxygenation (ECMO), an advanced life-support treatment used when the lungs cannot function adequately.

Could Hantavirus Become More Contagious In Future?

Virologists say viral mutation is a normal biological process, but not all mutations meaningfully change disease behaviour.

At present, there is no evidence the outbreak strain has evolved enhanced transmissibility. Public health experts say ongoing genomic surveillance remains critical because:

• viruses constantly evolve,
• outbreaks involving human-to-human spread require close monitoring,
• and early detection of major mutations can improve outbreak response.

Researchers are continuing to analyse viral samples from confirmed cases to better understand transmission patterns aboard the ship.

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What Should People Know About Risk?

Health authorities stress that hantavirus remains relatively rare globally. Most infections occur through rodent exposure rather than casual human contact.

Preventive measures include:

• avoiding rodent-infested areas,
• safely cleaning rodent droppings,
• improving ventilation in enclosed spaces,
• and using protective equipment during cleanup.

The CDC advises against sweeping or vacuuming rodent-contaminated areas directly because this may aerosolise viral particles. For the general public, experts say the immediate risk remains low despite ongoing monitoring of the cruise ship outbreak.

While the MV Hondius outbreak has raised international concern, health experts say current evidence does not suggest the hantavirus involved has mutated to become more contagious or severe.

Genetic sequencing shows the virus remains closely related to previously known South American strains, and several suspected international cases have now tested negative. Still, authorities continue global contact tracing and surveillance as researchers investigate how transmission occurred aboard the cruise ship. For now, experts emphasise that hantavirus remains primarily a rodent-borne infection, not a rapidly spreading respiratory virus like Covid-19.

Disclaimer: This content including advice provides generic information only. It is in no way a substitute for a qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.