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Scientists comment on the hantavirus situation on a cruise ship that travelled from Argentina to Cape Verde.
Prof Roger Hewson, Professor in Molecular Virology, London School of Hygiene & Tropical Medicine (LSHTM), said:
“Hantaviruses are a group of rodent-borne viruses that can cause severe disease in humans. They are found in different parts of the world, with different hantaviruses associated with different rodent hosts and different clinical syndromes. In the Americas, some hantaviruses can cause hantavirus pulmonary syndrome, a rare but potentially very severe illness affecting the lungs.
“The usual route of infection is exposure to infected rodents, particularly inhalation of virus from contaminated rodent urine, droppings or saliva. This is why investigations of suspected cases often focus on whether people may have had exposure to rodent-contaminated environments, food stores, cabins, storage areas or other enclosed spaces. Hantavirus is not generally considered easily transmissible between people.
“At this stage, based on the public information available, it’s important not to over interpret the cruise ship setting. The fact that cases have been identified in people associated with the same vessel does not by itself tell us whether exposure occurred on the ship, before boarding, during shore excursions, or through some other shared environmental exposure. That is precisely why public health investigations, laboratory confirmation and where possible, virus sequencing are important.
“Symptoms can initially be non-specific, including fever, muscle aches, headache and gastrointestinal symptoms, before some patients progress to respiratory illness. Diagnosis is usually made through specialist laboratory testing, including serology to detect recent infection and molecular tests where appropriate.
“The key public health message is that hantavirus infections are uncommon and the wider public risk is generally low. The priority is careful clinical management of affected individuals, laboratory confirmation, investigation of potential rodent exposure and proportionate public health follow-up of close contacts and shared environments.”
Dr Giulia Gallo, Postdoctoral Scientist in the Viral Glycoproteins Group, The Pirbright Institute, said:
What is hantavirus? Which parts of the world does it live in?
“Hantaviruses are zoonotic RNA viruses. They belong to the Bunyaviricetes class, which include other known human pathogens such as Rift Valley Fever virus, Oropouche virus, Lassa virus. Based on which part of the world they are found, they are classified as Old World Hantaviruses, found in Europe and Asia, and New World Hantaviruses, found in the Americas.
How do people contract hantavirus?
“The animal reservoirs of hantaviruses are rodents. Different species of rodents are the hosts of different hantaviral species, with a strict viral-host co-evolution and adaptation. Transmission occurs through inhalation of viral particles present in the excreta produced by rodents. For example, if people clean a house where rodents are found, they might come in contact with aerosols formed from droppings of infected animals, possibly becoming infected. Few reports suggests that most pathogenic hantaviruses could potentially transmit human-to-human, but a recent analysis published in 2021 suggests that there are not enough evidence to strongly support this way of transmission in humans. Further well-controlled cohort studies need to be carried out.
From what’s being reported, do we know how and why these cases might have arisen?
“Ongoing investigations from the WHO and its collaborators will shed light on the events that led to the three suspected cases reported on the cruise ship. The most likely situation is that people travelling from South America came in contact with infected rodents’ dropping in this part of the world. At the moment, we cannot be sure where the contact happened: it might have been during touristic activities in the region, or infected rodents might have been present on the ship. New World hantaviruses are considered the more pathogenic to humans, as compared to Old World Hantaviruses, causing a disease called “Hantavirus Pulmonary Syndrome”, which is believed to be fatal in 40% of cases. It can take up to a few weeks for the symptoms to manifest.
How is hantavirus tested for? What symptoms does it usually cause?
“Hantavirus infection can be tested using ELISA-based technique, detecting the presence of antibodies against the N protein of the virus, from blood samples. There are no rapid or at-home kits for hantaviruses.
“For Hantavirus Pulmonary Syndrome, the symptoms are quite unspecific and described as “flu-like”, with fever, myalgia, headache, nausea and overall fatigue. As the disease progresses, the lungs and heart become affected, with shortness of breath, hypotension, chest pain. The patient would require intensive care and support for breathing for survival.
What’s the relevance of this being on a cruise ship – is that likely relevant or don’t we know yet?
“As mentioned, for the most pathogenic New-World hantavirus Andes virus, there are a few papers describing possible human-to-human transmission. However, at this stage, we can’t confirm that the phenomenon we are seeing on the cruise relates to this (ships being enclosed environments where human-to-human transmission might happen more easily), which would be very unlikely, and as previously described, not necessarily supported by the literature and evidence. It seems much more realistic that people were individually exposed to rodents’ droppings in South America, or infected rodents boarded or were already present on the ship, and people came in contact with their excreta. It would be necessary to identify any potential source of infection on the ship, and trace back the journey of the patients, to know if they visited American regions were hantaviruses are reported.”
Dr Toshana Foster, Associate Professor in Molecular Virology, University of Nottingham, said:
What is hantavirus? Which parts of the world does it live in?
“Hantaviruses are a large family of RNA viruses which co-evolved silently in rodent hosts, particularly mice and rats. These viruses are found worldwide where the rodent species that carry it live, so they are found in North and South America to Europe, Russia and Asia. The hantaviruses that are found in Europe and Asia usually are associated with haemorrhagic fever with renal syndrome (HFRS), a kidney disease which has a variable case fatality rate (CFR), depending on the infecting type/strain of hantavirus, ranging from 0.1% to 15%. The hantaviruses that are endemic in the Americas are of higher clinical concern, they lead to hantavirus cardiopulmonary syndrome (HCPS), which has a higher CFR of 30-40%.
How do people contract hantavirus?
“The virus is spread to humans if aerosolised virus is breathed in from urine, droppings, through direct contact or through a rodent bite. Most often people are unaware of the risk of catching the virus, as cases are contracted through aerosolised virus particles. In South America, however, the Andes (ANDV) hantavirus which is endemic in Chile and Argentina, is so far is the only hantavirus known to spread from human to human, through close contact.
From what’s being reported, do we know how and why these cases might have arisen?
“It would be unwise to speculate at the moment, but from what has been reported, the likely explanation is that there was an exposure to infected rodents or their droppings at some stage of the trip. Seeing a small cluster of cases is unusual however given how hantaviruses usually spread, where human to human transmission is rare. A concerning scenario, would involve a strain of ANDV spreading from person to person on the ship, but this would require confirmation through laboratory testing and sequencing of the virus.
How is hantavirus tested for? What symptoms does it usually cause?
“There are a few tests that would confirm hantaviruses present in the blood of patients – these are antibody or serology tests (ELISA) to assess whether the body has made antibodies specific to the virus. Another is a polymerase chain reaction method, which would detect the genetic make-up of the virus even before antibodies are made by the patient. This would identify what strain/type of virus is infecting the patient.
“Symptoms are often mistaken for the flu initially as they typically are fever, muscle aches, headache, fatigue, vomiting and abdominal pain. In milder cases of HFRS, infected people may notice reduced urine output and back pain due kidney injury. These symptoms can then progress, in the worst cases to chest tightness, shortness of breath, dry cough and respiratory failure.
What’s the relevance of this being on a cruise ship – is that likely relevant or don’t we know yet?
“The nature by which hantaviruses usually spread often involves individual cases due to a single encounter with an infected rodent. Multiple cases linked to a single event have not been reported to occur often. Whether the fact that the outbreak is on the cruise ship is relevant will be confirmed once more is known about hantavirus identity. The cruise ship is a closed environment where facilities and air handling systems are shared and could amplify person to person transmission if the hantavirus is capable of this.”
Prof Sir Andrew Pollard FRCPCH FMedSci FRS, Ashall Professor of Infection and Immunity, Pandemic Sciences Institute, and Director of the Oxford Vaccine Group, University of Oxford, said:
“Hantaviruses are a family of viruses that are related but the family members in the America’s (New World hantaviruses) generally cause a life-threatening respiratory illness whereas the Old World viruses (which are found in Europe) cause bleeding and kidney problems, with a much lower case fatality rate. Within these families there are different varieties of hantaviruses that infect different rodent species. Most human cases involve exposure to rodents or material from them (urine, faeces or saliva). Spread between people is very unusual and so wider spread to the public is extremely unlikely. There are no specific treatments for the hantavirus respiratory syndrome and affected patients usually need intensive care. There are no approved vaccines in Europe in North America to prevent hantavirus disease.”
Prof Jon Cohen, Emeritus Professor of Infectious Diseases, Brighton and Sussex Medical School, said:
“Hantaviruses are a group of viruses that occur throughout the world often with rather exotic names that show where they were first found (such as Andes virus that is found in Argentina), although they cause rather different diseases depending on their location. The New World viruses, found in North and South America, cause Hantavirus Pulmonary Syndrome (HPS), a particularly severe form of infection. After flulike early symptoms the person develops low blood pressure, difficulty with breathing, build up of fluid in the lungs, kidney failure and often uncontrolled bleeding.
“All hantaviruses are associated with small rodents, such as mice and rats, and the likelihood of exposure depends on human and environmental factors such as harvest time (working in the fields) and probably, global warming as it affects rat population density, for example. Infection occurs due to close exposure to mouse or rat urine. Person-to-person spread is uncommon.
“There is not a particular reason for these infections to occur on cruise ships, but the source of infection in this case is still unknown.
“The infection is diagnosed with a blood test. There is no specific antiviral treatment so supportive care, often in an intensive care unit, is needed.”
Dr Benjamin Brennan, Group Leader and Senior Lecturer, MRC-University of Glasgow Centre for Virus Research, University of Glasgow, said:
What is hantavirus? Which parts of the world does it live in?
“Hantaviruses (named after the Hantaan river in Korea) are a family of viruses that are rodent-borne and are transmitted by animals such as rats and voles. Very broadly the viruses are found throughout the Americas and are also found in Northern Europe. Hantavirus disease comes in two main forms: a cardiopulmonary (severe respiratory distress) syndrome caused by viruses found in the americas; or patients can experience haemorrhagic fever with renal disfunction if infected with the European/asian lineage viruses.
How do people contract hantavirus?
“Hantaviruses are transmitted by people coming into contact with rodent excreta (dried urine/faeces). It is usually associated with cleaning/dusting properties that have been dormant over winter where rodents have encroached into the property. They are very rarely transmitted directly from person to person. It is nearly always due to contact with infected rodents or their bodily fluids.
From what’s being reported, do we know how and why these cases might have arisen?
“Not enough information is known about how this outbreak started. But due to the strong linkage to rodent-borne transmission, rodents are likely to be somehow implicated.
How is hantavirus tested for? What symptoms does it usually cause?
“Hantaviruses are not routinely tested for due to the rare nature of the infections. Formal diagnoses in the UK would be confirmed at specialist diagnostic laboratories e.g. the Rare & Imported Pathogens Laboratories at UKHSA. Symptoms are described above, the disease usually starts with flu-like illness and fever that resolves within a week. However, if the disease progresses to the syndromes described above, they can be fatal.
What’s the relevance of this being on a cruise ship – is that likely relevant or don’t we know yet?
“Infectious disease outbreaks on cruise liners are not uncommon (e.g. norovirus). We don’t yet know whether it’s relevant that this current situation has happened on a cruise ship.”
Dr Liam Brierley, Research Fellow, MRC-University of Glasgow Centre for Virus Research, University of Glasgow, said:
“Hantaviruses are a type of virus that are carried by wild rodents like mice or rats and have been recognised since the 1980s. They are transmitted to humans through breathing in virus in aerosol that has been shed from rodent droppings, but they do not transmit well and so most outbreaks happen among people who have a very high amount of exposure to droppings like farm workers in parts of the world where farmland overlaps with wild habitat for many rodents.
“Hantaviruses can be found in wild rodents over many parts of the globe including North and South America, Asia, and Europe which includes wildlife of the United Kingdom although human infection with these viruses is exceptionally rare.
“In terms of disease, there are two main types of hantavirus – one can cause disease in the kidneys with intensive fever (“Haemorrhagic Fever with Renal Syndrome” or “HFRS”), the other can cause disease in the lungs (“Hantavirus Pulmonary Syndrome” or “HPS”). While these are life threatening, most hantavirus infections do not progress to this stage of disease and they are more likely to do so in people with underlying health conditions. Certain specific hantaviruses are also milder than others, though it is currently hard to speculate as we don’t yet know which of these diseases or which specific hantaviruses affected the people on the MV Hondius. So far only one case has so far been confirmed positive for hantavirus at all.
“Importantly, hantaviruses are not transmissible from person to person except in extremely rare circumstances and only for one specific type of hantavirus called Andes virus, under very intensive close contact (e.g., between sexual partners or from hospital patient to hospital staff). It’s therefore extremely likely that these cases have resulted from the same single point of exposure to rodents. The long incubation period means that it will be challenging to pinpoint exactly when and where this occurred.”
Dr Charlotte Hammer, Assistant Professor and infectious disease epidemiologist, University of Cambridge, said:
“Hantavirus describes a family of viruses that are zoonotic, i.e. transmitted from animals to humans. There are two major lineages of hantavirus: Old World Hantaviruses and New World Hantaviruses. Old World Hantaviruses are found in Europe and Asia, New World Hantaviruses are found in the Americas. In the current case we are most likely talking about Andes virus, which is a New World Hantavirus found in Argentina.
“The danger with New World Hantaviruses is that they are both unspecific in early presentation which resembles flu-like diseases, and the progression to Hantavirus Pulmonary Syndrome which can be very severe with a case fatality rate of up to 40%. Treatment is mainly supportive. Given that the incubation period is one to eight weeks, more cases are still possible.
“The most common route of Hantavirus spread is via rodents and their droppings (saliva, faeces or urine which can be aerosolised for example when cleaning, less commonly through bites and scratches), human-to-human transmission is possibly but very rare. Given the timeline, there are multiple possible scenarios in this case: it is not entirely uncommon for rodents to hitch a ride on a ship which would be one possibility, people having been infected when the ship last made port in Argentina is another possibility especially given that incubation periods of up to eight weeks, and the last possibility would be human-to-human transmission which particularly at scale would be very unlikely.”
Prof Paul Hunter, Professor in Medicine, UEA, said:
“Hantavirus is a viral infection that is acquired from contact with infected rodents (mice and rats). The virus is typically spread from rodents to humans through airborne aerosols of faeces and urine. There have been some suggestion that person-to-person spread may occur but there is still no agreement on this and others have concluded that evidence of person-to-person spread is not confirmed. If person-to-person spread happens at all it is rare.
“There are several different types of Hantavirus each associated with a different rodent. The infection can present as hantavirus pulmonary syndrome (HPS) and haemorrhagic fever with renal syndrome (HFRS). The different types tend to cause one or other of the clinical syndromes. Mortality rate in diagnosed infections is high, in HPS this can be about 30% and in HFRS about 10%. Mortality rates are generally higher in older people, and often people on cruises tend to be older. There is no specific antiviral treatment available. Whilst some vaccines are available they do not affect all types of the virus.
“It is too early to speculate on how the affected people became infected. But it is very unlikely that this outbreak would lead to an increased risk in the UK or elsewhere in Europe.”
Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:
“When hearing about outbreaks on cruise ships, we tend to think of other diseases like COVID-19 or norovirus. Hantavirus is rarely associated with this setting, and person-to-person spread of the virus is also unusual.
“Given the ship came from South America, it’s plausible that the Andes strain of the virus may be responsible for this outbreak. There is previous reporting of person-to-person transmission from the Andes strain, though it’s not yet certain whether that’s the case here. PCR testing would be needed to confirm whether this is the Andes strain.”
Declared interests
Prof Roger Hewson: “I am Professor of Virology at the London School of Hygiene & Tropical Medicine and am also employed part-time by the UK Health Security Agency. These comments are made in my academic capacity at LSHTM and do not represent an official UKHSA statement. UKHSA media enquiries should be directed to ukhsa-pressoffice@ukhsa.gov.uk.”
Dr Giulia Gallo: “I have no conflict of interest.”
Dr Toshana Foster: “I declare that I do not have any conflicting interests.”
Prof Sir Andrew Pollard: “Nothing I can think of for hanta.”
Prof Jon Cohen: “I have no conflicts to declare.”
Dr Benjamin Brennan: “No COIs to declare.”
Dr Liam Brierley: “I disclose previous funding for work unrelated to hantaviruses from CSL Seqirus Ltd.”
Dr Charlotte Hammer: “I have no interests to declare.”
Prof Paul Hunter: “No COIs.”
Dr Michael Head: “No COI to declare.”