Amid public concern about the potential for the deadly hantavirus to occur in Australia, it has been reported that four Australian passengers from the affected cruise ship - two believed to be from Queensland - will be quarantined in Perth for three weeks.
Senior academics from the University of the Sunshine Coast discuss the issue from the disciplines of microbiology and nursing (infection prevention and control).
They say that while risks for everyday Australians remain low at this stage, Australian healthcare workers must remain vigilant for imported cases, as their direct contact with patients and clinical samples places them at highest risk of exposure.
What are hantaviruses?
Hantaviruses (Hantaviridae) are a group of over 20 different viruses that are carried naturally and asymptomatically in rodents such as rats and mice, and less commonly in other small mammals such as shrews and microbats.
Not all hantavirus species can spread from rodents to humans. No known cases of hantavirus have spread from microbats to humans - the primary vector of concern is rodents. Every year, about 150,000 hantavirus cases occur around the world.
Australia is the only inhabited continent that has never recorded a locally acquired human hantavirus infection - despite a quarter of a century of monitoring and testing. This is because none of the hantaviruses found naturally in Australian rodents are thought to cause human infections.
This situation isn't unique to hantavirus - Australia is also the only inhabited continent that has no local cases of plague, a disease that killed about half of Europe's population during the Black Death pandemic in the 1300s.
How are most hantavirus infections acquired?
Hantavirus infection most often occurs by inhaling the dried-out droppings, urine or saliva of rodents in infested environments. This contaminated dust can be stirred up by activities such as sweeping or vacuuming, where it becomes airborne and breathed in, especially in poorly ventilated areas and enclosed spaces. Infection can also occur through skin cuts (including from rodent scratches and bites), or from touching the eyes, nose or mouth with contaminated hands or material.
While Australia doesn't naturally have hantaviruses that can spread from rodents to humans, rodent droppings can harbour other nasty pathogens that can cause, for example, leptospirosis or rat-bite fever. Wearing a N95/KN95 (or better) respirator and non-permeable gloves is always recommended when dealing with rodent waste, and to follow good hygienic practices such as laundering clothes and soap-based handwashing.
What are the symptoms of hantavirus infection?
Symptoms of hantaviral infection arise between one and eight weeks after virus exposure. Early symptoms include flu-like symptoms such as fever, tiredness, muscle aches, headaches, chills, and dizziness. Some people may present with gastrointestinal symptoms such as pain, diarrhoea, vomiting and nausea.
About a week later, symptoms may progress to feeling short of breath, a tight chest, coughing and breathing more shallowly. This is because the lungs are filling up with fluid from leaking blood vessels. This is a very serious phase of the disease, which can progress to reduced oxygen levels, low blood pressure, heart issues, shock and death.
What prior outbreaks of hantavirus have occurred?
As hantaviruses naturally occur in rodents in Europe, Asia and the Americas, human hantavirus infections are somewhat common, but they usually only occur following inhalation of rodent-contaminated dust. Human outbreaks are relatively rare.
One such outbreak happened in the northern hemisphere summer of 2012, where there was a large hantavirus outbreak causing pulmonary disease in Yosemite National Park, in central California.
During the winter off-season, deer mice, which are natural vectors for Sin Nombre hantavirus (Orthohantavirus sinnombreense), infested tent cabins by tunnelling into the foam insulation. Of the 10,000 guests who stayed in these cabins over a 1.5-month period, 10 became infected with this virus - a 1 in 1000 infectivity rate. Eight infected people developed hantavirus cardiopulmonary syndrome, five were on ventilators in intensive care, and three died.
The Yosemite National Park outbreak patients all acquired their infection from breathing in rodent waste-contaminated dust. This is because the outbreak was caused by Sin Nombre virus, which isn't known to transmit from person-to-person. This virus is the same hantavirus species believed to have killed Gene Hackman's wife, Betsy Arakawa.
Cruise Ship MV Hondius Docks In Tenerife. Photo by Chris McGrath/Getty Images.
How does this cruise ship outbreak differ?
The MV Hondius cruise ship outbreak is being caused by Andes virus (Orthohantavirus andesense), the only hantavirus known to spread from person to person. Andes virus infections are rare. Prior to the current outbreak, only 3,000 cases had ever been recorded, with about one in 10 linked to human-to-human transmission.
Andes virus was first identified 31 years ago following an outbreak in the Andean region of Chile and Argentina. An outbreak the following year confirmed this particular virus could spread from person to person.
The natural rodent host of Andes virus is the long-tailed pygmy rat (Oligoryzomys longicaudatus), which lives in moist areas, especially scrubs, road verges and forests in Chile and Argentina. Its population numbers drastically increase with food availability, which is when the risk to zoonotic virus transfer to humans has historically been highest.
Although we don't yet know exactly where the first cruise ship passenger was infected, it was almost certainly somewhere in Argentina or Chile, because that's where the host rodent lives. Genomic typing has confirmed that the virus infecting cruise ship passengers is the Andes virus. This is concerning because of the known human-to-human transmission, and the fact that virtually all cruise ship passengers would have had relatively close contact with infected individuals.
Why is Andes virus on a cruise ship such a concern?
Most of what we know about Andes virus is from a large outbreak that occurred in Epuyén, Argentina, in late 2018 and early 2019. This outbreak resulted in 34 confirmed infections, three superspreader events, and 11 deaths. This outbreak was the first time that epidemiologists confirmed that Andes virus infection could occur after only a fleeting interaction with an infected person. In this case, a symptomatic, infected man attended a birthday party with 100 other people. He infected two people sitting at his table, another two people sitting at an adjacent table, and one person he crossed paths with only briefly while going to the restroom.
The cruise ship situation is evolving quickly, with nine confirmed and two probable cases to date, and more likely to follow. So far, all infections are in cruise ship passengers or crew. This outbreak is following a similar pattern of person-to-person transmission seen in prior Andes virus outbreaks, with people most at risk of infecting others when symptomatic.
However, there is emerging evidence that, in certain cases, the virus can be transmitted up to 48 hours before someone becomes symptomatic, and then up to 48 hours after they develop symptoms. This latter stage is known as the 'prodrome phase', which is when someone has non-specific flu-like symptoms that can easily be confused with other respiratory infections like influenza or RSV.
Two repatriated cruise ship passengers from Spain and the US who were asymptomatic tested positive to Andes virus via PCR, which is worrisome, as it adds more evidence that people may be infectious to others without knowing that they're carrying this potentially deadly virus.
Like Sin Nombre virus, Andes virus has a case fatality rate of 35-50 percent. The current outbreak's case fatality rate is 27 percent. It hopefully will stay on the lower end as new infections are identified and treated at an early stage.
Passengers wave from a bus as Dutch Embassy staff wave them off after being evacuated from the MV Hondius after docking. Photo by Chris McGrath/Getty Images.
What are treatment options?
There is no vaccine and no targeted antiviral treatments available for hantavirus. Treatment is primarily supportive care for patients whose health is declining rapidly, such as oxygen therapy, breathing support and fluid management to prevent cardiac and breathing issues. For people who survive a hantavirus infection, it can take a long time to recover, with similar symptoms to long COVID such as ongoing tiredness, muscle weakness and difficulties tolerating exercise.
What is the risk to Australia?
As we learned during COVID, Australia's geographically isolated island location means we are currently at very low risk of hantavirus outbreaks in our community. We do not have the rodent species that would lead to Andes virus becoming endemic in Australia, so our only risk is through imported cases from travellers.
The Federal Government's announcement that it will enforce a strict three-week quarantine for the repatriated Australian and New Zealand residents and flight crew is good news, although it may need to be longer given the long latency period between hantavirus exposure and symptom onset, which can be as long as eight weeks.
The bigger risk to our country at the moment is from travellers who had contact with cruise ship passengers prior to Andes virus confirmation, and their contacts. About 34 passengers and crew disembarked the MV Hondius at St Helena between 22 April and 24 April before the outbreak was confirmed on 2 May, following the death of the third case.
One member of this group, the wife of the index case, died in hospital shortly after flying into Johannesburg, South Africa, and another person subsequently tested positive and is currently in hospital in Switzerland. An additional probable positive case had disembarked at Tristan da Cunha on 14 April and became symptomatic on 28 April.
There is now a large, coordinated, international public health effort underway to trace the contacts of these 34 people, spanning four continents and numerous countries - an incredibly complex public health task. Residents on St Helena, Ascension Island, and Tristan da Cunha are at high risk of infection due to large numbers of cruise ship passengers and staff liaising with locals on these islands whilst potentially infectious.
How should healthcare workers prepare for this risk?
Like COVID, the elevated risk to Australian healthcare staff cannot be overstated. Twelve Dutch healthcare workers have just entered mandatory six-week quarantine due to improper handling of hantavirus-contaminated blood and urine from a hospitalised patient. This response from Dutch authorities is warranted because hantavirus infection can occur by breathing in contaminated human body fluids. Any patient interactions and specimen handling procedures will require well-trained staff to implement heightened personnel protective equipment, biosafety and biocontainment procedures.
Frontline healthcare workers including nurses, doctors, paramedics, laboratory and support staff should remain alert for potentially infectious patients, particularly those with recent travel history or contact with travellers. They should adopt appropriate protective measures, including N95 masks in addition to gloves, gowns and eye protection, and adhere strictly to established safety procedures.
Australia is the only inhabited continent that has never recorded a locally acquired human hantavirus infection – despite a quarter of a century of monitoring and testing. This is because none of the hantaviruses found naturally in Australian rodents are thought to cause human infections.
What can I do to protect myself and my family?
If you're concerned about hantavirus, especially if you're travelling overseas soon, the best way to protect yourself and your loved ones is to wear an N95 or KN95 (or higher) respirator in places where there's poor ventilation and you'll be in contact with other people. Wearing a respirator will also protect you from catching other infectious respiratory pathogens like influenzavirus, RSV, adenovirus, human metapneumovirus, human parainfluenza virus, SARS-CoV-2 and other coronaviruses, and rhinovirus.
These respirators are widely available in Australia through pharmacies, major supermarkets, hardware stores and online retailers.
Because infection can also occur through contact with contaminated fluids, it's important to wash your hands regularly or use hand sanitiser, avoid touching your face, and take care with shared or frequently used surfaces. Hantavirus could survive from a few hours to a few days on surfaces, so simple precautions like wiping down areas such as aeroplane tray tables and washing your clothes and hair after long travel journeys can provide an added layer of protection.
