Health authorities are closely monitoring the Andes strain of hantavirus after several deaths linked to the cruise ship “MV Hondius” have raised concerns because, unlike most hantaviruses, the Andes virus may spread between humans.

According to updated information from the tour operator, 30 passengers left the ship during a stopover at St. Helena, including passengers from Germany. Among them was a Dutch woman who later died in Johannesburg from a hantavirus infection.

Authorities identified eight known or suspected cases, including three confirmed infections. The cases included a British patient receiving intensive care in Johannesburg, a Swiss patient undergoing treatment in Zurich, and several suspected cases in Germany and Netherlands.

A flight attendant who had been in contact with an infected Dutch passenger was also admitted to a Dutch hospital with symptoms suggestive of hantavirus infection. The Dutch Health Ministry confirmed that the woman showed symptoms that could indicate hantavirus infection. She briefly boarded a KLM flight, but the crew prevented her from continuing the journey because of her health condition.

The cruise ship is now heading toward the Canary Islands. According to government officials, the evacuation of all passengers could begin on May 11 immediately after the ship docks.

Experts interviewed by the Science Media Center, Germany assessed the evolving situation.

Virus Risks

The Andes virus belongs to the Hantavirus family and is found mainly in South America. Various rodent species, particularly rice rats, are considered natural hosts.

The virus can cause Hantavirus cardiopulmonary syndrome (HCPS), a severe, often fatal respiratory disease affecting the lungs and cardiovascular system. Symptoms often begin with flu-like symptoms, such as fever, headache, and muscle pain. Severe cases can lead to shortness of breath and life-threatening respiratory failure.

Researchers consider the Andes virus more dangerous than the Hantavirus strains prevalent in Europe because of its higher mortality rate and the possibility of human-to-human transmission. The incubation period may last for several weeks and, in rare cases, for up to 42 days. Currently, there is no approved vaccine or targeted antiviral treatment.

“Confirmation of the Andes virus makes the situation more serious but not automatically uncontrollable,” said Roman Wölfel, MD , PhD, senior physician, director of the Bundeswehr Institute of Microbiology and professor at the Technical University of Munich, Munich, Germany.

Most hantavirus do not typically spread between humans. “The Andes virus is the key exception here: Limited instances of human-to-human transmission have been reported for this South American hantavirus type, particularly during very close and prolonged contact,” Wölfel said. “Therefore, human-to-human transmission must now be treated as a realistic working hypothesis.”

For each of the newly identified cases, researchers should determine whether shared exposure to rodents in South America may better explain the infections.

However, there are a few peculiarities. “As far as we know, the Andes virus does not behave like classic highly contagious respiratory viruses such as influenza or coronaviruses”, he said. “Transmission between individuals appears possible mainly through close contact with infected individuals, for example through exposure to saliva or respiratory secretions at close range”.

The exact mechanism of transmission has not yet been clearly established. Researchers are evaluating several possible routes, including direct contact with infectious secretions or exposure to larger respiratory droplets at a close range. Aerosols may also contribute under certain circumstances. However, according to Wölfel, long-distance transmission through routine daily contact or ventilation systems appears unlikely.

Clinical Differences

In Germany and other EU countries, Old World hantaviruses are detected most often, particularly Puumala virus and Dobrava-Belgrade virus, which are the most significant human pathogens. “These viruses can also cause serious illness. In Germany, this usually involves kidney damage”, said Roland Schwarzer, head of the research group, from the Institute for Translational HIV Research from the University Hospital Essen, in Essen, Germany. “However, compared with Andes virus infections in South America, they are generally considered much less lethal overall.”

Most importantly, no human-to-human transmission has been documented for hantaviruses found in Germany or elsewhere in Europe. Infection usually occurs through exposure to excretions from infected rodents, such as inhalation of contaminated dust, Schwarzer explained.

Risks

“For individuals directly affected, particularly older adults or travelers who had close contact with infected individuals, there is a serious health risk because the Andes virus circulating in South America can cause severe illness and carries a comparatively high mortality rate,” according to Martin Eiden, PhD senior researcher from the Institute of Novel and Emerging Infectious Diseases, Friedrich-Loeffler-Institut, Greifswald-Insel, Riems, Germany.

However, the risk for widespread transmission in Germany and Europe remains low. “The main reason is that natural animal hosts of the Andes virus, such as rice rats and dwarf rice rats, are not found here, making sustained transmission unlikely,” Eiden said. In addition, confirmed cases of human-to-human transmission are extremely rare. “Nevertheless, the incident highlights the importance of international health surveillance, rapid diagnostics, and transparent communication during the event of unusual infectious disease outbreaks.”

Overall, according to Eiden, there is currently no reason for widespread concern in Europe, although the situation warrants close monitoring.

What Happens Next?

The cruise ship is now heading toward the Canary Island of Tenerife, Spain. The remaining passengers and crew members will undergo medical evaluation and receive treatment at a clinic specializing in epidemic response.

“For the passengers and relevant contacts of the Swiss patient, confirmation of Andes virus infection means that precautionary risk assessment and active contact tracing are necessary,” advised Jonas Schmidt-Chanasit , MD, deputy director of the Arbovirus and Entomology Department at the Bernhard Nocht Institute for Tropical Medicine in Hamburg, Germany.

The key step involves assigning individuals to contact risk categories. Individuals who had close, prolonged, or unprotected exposure to infected individuals, such as cabin mates, close travel companions, caregivers, or healthcare professionals with unprotected exposure, should undergo close monitoring and may require quarantine depending on the assessment by health authorities, according to Schmidt-Chanasit. For casual contact, such as brief encounters without close contact, the risk is extremely low.

He added: “Because of the long incubation period of HCPS, follow-up monitoring for several weeks is advisable.” However, the blanket quarantine of all individuals, regardless of exposure risk, is not automatically proportionate. “A risk adapted strategy makes more sense: strict isolation of confirmed or highly suspected cases, active symptom monitoring of relevant contacts, rapid testing after symptom onset, and clear protective measures for healthcare professionals.”

Conclusion: Vigilance, Not Panic

The outbreak of the rare Andes virus on the “Hondius” has placed health authorities worldwide on high alert because, unlike most other hantaviruses, this pathogen may also spread from person to person. Experts emphasized that only a small number of cases have been reported so far and that transmission appears limited to close contact.

Currently, the risk for a major outbreak in Europe is low. Nevertheless, extensive testing, contact tracing, and precautionary measures are underway to identify additional infections at an early stage.

This story was translated from Medscape’s German edition.