Why the hantavirus outbreak is different from COVID-19 

The last of the passengers on the hantavirus-struck MV Hondius cruise ship have been flown to the Netherlands. But new cases are emerging as researchers race to track down where the outbreak originated.

As authorities seek to arrange quarantines and access to health facilities for the passengers, communities where some of the passengers have gone have responded with anger and protests against what many perceive as risk of exposure to the virus.

At the heart of those fears is the collective experience the world suffered through six years ago with the COVID-19 pandemic, which sent the planet into lockdown and killed nearly 15 million people in two years.

But the hantavirus is very different from COVID-19 in how it spreads, how deadly it is and how likely it is to trigger another global crisis, public health experts said.

“I need you to hear me clearly: this is not another COVID. The current public health risk from hantavirus remains low. My colleagues and I have said this unequivocally, and I will say it again to you now,” Tedros Adhanom Ghebreyesus, the director general of the World Health Organization (WHO), said in a statement on Saturday.

Here is a a breakdown of the key differences between the hantavirus and COVID-19:

What is the hantavirus?

Hantaviruses are a family of viruses that cause two main illnesses in humans. One is known as hantavirus pulmonary syndrome (HPS) and primarily attacks the lungs. The other, haemorrhagic fever with renal syndrome (HFRS), mainly affects the kidneys.

The viruses are named after the Hantan River in South Korea, where the first virus belonging to the family was isolated in 1978. By that time, researchers had tried for decades to identify the cause of what was known as the Korean haemorrhagic fever, which afflicted 3,000 United Nations soldiers during the Korean War from 1951 to 1953.

The virus is a rare infection transmitted to humans by rodents. The virus is most commonly spread by infected rodents, which can carry it in their urine, saliva and droppings. When these materials dry out and become airborne, humans can become infected by inhaling the contaminated particles.

HPS attracts the most attention because it has a high fatality rate, killing about 40 percent of the people it infects, according to the US Centers for Disease Control and Prevention (CDC). The death rate for HFRS is less clear with studies suggesting anything from about 1 percent to 15 percent.

Hantavirus pulmonary syndrome usually begins with flu-like symptoms, such as fatigue and fever, between one and eight weeks after exposure, according to the CDC. Four to 10 days later, coughing, shortness of breath and fluid in the lungs appear. Diagnosis in the first 72 hours of infection is difficult, the CDC said, and symptoms can easily be mistaken for the flu.

Research suggested hantaviruses have circulated for centuries with outbreaks recorded in parts of Asia and Europe.

A previously unknown group of hantaviruses emerged in the early 1990s in the southwestern United States, causing a severe respiratory illness now known as hantavirus pulmonary syndrome. The CDC began tracking the disease after a 1993 outbreak in the Four Corners region, where the states of Arizona, Colorado, New Mexico and Utah meet.

The Andes strain of the hantavirus, which causes HPS, is the only hantavirus clearly shown to spread from person to person to a limited extent. The virus detected among passengers of the MV Hondius was the Andes strain, which drives most HPS cases in Chile and Argentina, where the MV Hondius cruise began.

According to the WHO and public health experts, person-to-person transmission of the hantavirus is rare and occurs as a result of close, prolonged contact, such as close proximity within the same household or intimate contact. It does not spread like an airborne virus through casual social contact.

“Occasional human-to-human transmission events may occur but require specific circumstances and long exposure times,” Tomas Strandin, a virologist and university researcher at the University of Helsinki in Finland, told Al Jazeera. “However, infections via rodents are becoming more widespread due to climate change, but these are local infection events.”

The WHO on Tuesday confirmed the 11th hantavirus infection from the MV Hondius outbreak after Spain’s Ministry of Health said a Spanish passenger had tested positive.

The announcement was made the day after the evacuation of the cruise ship was completed. The Dutch Ministry of Foreign Affairs said on Monday that two planes carrying the final 28 evacuees had landed in the Netherlands.

Their arrival from Spain’s Canary Islands concluded a complex operation in which 94 people were evacuated and repatriated to about 20 countries where they have entered a period of quarantine.

Officials from the US Department of Health and Human Services said on Monday that one of the 18 American passengers evacuated from the ship had tested positive at a biocontainment unit in Nebraska while the others are being monitored and tested after potential exposure.

The MV Hondius, which departed from South America on April 1, anchored at a port on Tenerife for the evacuation. A total of 150 people from 23 countries were on board the ship when it left Argentina, and some had disembarked before the ship reached the Canaries.

Three people – a Dutch couple and a German tourist – have died in the hantavirus outbreak on the ship.

The ship is now on its way to the Netherlands, where it will be disinfected.

According to a hypothesis by the European Centre for Disease Prevention and Control (ECDC), the European Union’s principal disease prevention agency, some of the ship’s passengers caught the hantavirus while spending time in Argentina before boarding the MV Hondius. The hantavirus is endemic to Argentina, which means the virus is constantly present and has a predictable and relatively stable prevalence there.

While evacuations of the passengers were under way, Gianfranco Spiteri, ECDC’s head of global epidemic intelligence, told Al Jazeera: “Passengers and crew continue to disembark and to be medically evacuated to their countries of origin. At disembarkation, they are all considered high-risk and repatriated, whether symptomatic or not, through noncommercial flights.”

“ECDC continues to work closely with the [EU] member states, the European Commission, WHO and other partners to support a coordinated response and information-sharing. In connection with this outbreak, ECDC rapidly engaged the EU Public Health Reference Laboratory for emerging, rodent-borne and zoonotic viral pathogens to provide support to the member states to ensure rapid and high-quality diagnostics.”

Medical experts said they believe the measures governments are currently taking are adequate.

“Quarantine of individuals with potential exposure is important, and quarantine should be extensive since the virus may present an incubation period for up to several weeks during which it is undetectable,” Strandin said.

How are hantaviruses different from COVID-19?

Hantaviruses and coronaviruses, several strains of which cause COVID-19, are both ribonucleic acid (RNA) viruses, which means they use RNA as their genetic material instead of DNA. But the viruses have key structural differences.

Coronaviruses have a prominent spike protein protruding from their surface, which gives them a crown-like appearance. Hantaviruses, on the other hand, have a shell made up of hooks called glycoproteins, which form a grid-like pattern. A glycoprotein is a molecule that’s part protein, part sugar.

This structural difference is primarily why COVID-19 is highly contagious while hantaviruses are not nearly as transmissible. The COVID-19 spike protein is the part of the virus that allows it to attach itself to human cells.

Human cells have tiny protein structures called ACE2 (angiotensin‑converting enzyme 2) receptors, which can act as docking stations for certain viruses. The COVID-19 spike protein has adapted to easily latch onto the ACE2 receptors, which are abundantly present in the upper respiratory system, including the nose and throat.

The virus can easily replicate while latching onto these receptors, making several copies of itself that can be coughed or sneezed out. This can release tiny droplets or aerosols containing the virus into the air. Another person nearby can inhale them, and the droplets can enter their nose, throat and lungs and cause an infection.

The glycoproteins in the hantavirus structure, on the other hand, don’t latch onto ACE2 receptors, but instead bind to β3 integrins, which are receptor proteins found on human cells. Unlike ACE2 receptors, β3 integrins are located deep in the lungs and on the inner lining of blood vessels. As a result, hantaviruses primarily infect the lower respiratory system and the blood vessel lining, causing leakage and serious illness there. So if a person infected with a hantavirus sneezes or coughs, their droplets might contain some virus but generally not very much, which helps explain why human-to-human spread is rare.

Additionally, COVID-19 is a positive-sense RNA virus. This means that upon entering a human host, it immediately starts to replicate. Hantaviruses are negative-sense RNA viruses, having to go through an extra step to become positive-sense viruses before they can start replicating.

COVID-19 has a short incubation period, from two to 14 days, allowing for rapid spread. Hantaviruses have a longer incubation period, from one to eight weeks, which also slows down transmission.

However, Strandin said, while COVID-19 is typically “better controlled in previously healthy individuals”, hantaviruses “can cause severe infections in healthy younger individuals”.

And if a hantavirus does manage to infect the upper airways, it becomes easier for it to leave the body in droplets when someone breathes, talks, coughs or sneezes. Because the Andes strain is one of the few hantaviruses with documented person‑to‑person transmission, it might be a variant that does enable infection of the upper airways, Strandin said.

“Andes hantavirus may be different from other hantaviruses in that it could infect upper respiratory airways eventually due to high systemic virus loads, but this is rare,” he said.

Spiteri said people who develop symptoms should be assessed quickly and, if needed, evacuated to hospitals that can provide intensive care.

“Anyone with symptoms is tested after leaving the ship, but a negative test doesn’t always rule out infection, so follow‑up is still important,” he said.

He added that healthcare workers caring for sick passengers should use protective gear to prevent close contact transmission and stronger precautions are needed if treatment procedures could create airborne particles.

“Passengers who leave the ship have received clear instructions on what to do and what symptoms to watch for until doctors can confirm whether they are infected. Passengers and crew who may have been exposed should be monitored for symptoms after leaving the ship and referred for medical care if needed,” he said. “According to ECDC’s scientific advice, passengers and crew who have symptoms require immediate medical isolation, testing and medical care while those who do not have symptoms are asked to quarantine and monitor for symptoms for up to six weeks.”

Could a hantavirus cause the next pandemic?

Experts said the low chances of human-to-human transmission make it almost “impossible” for hantaviruses to cause the next pandemic.

A pandemic is a fast‑spreading epidemic that affects many countries. Besides COVID-19, other pandemics have included the H1N1 swine flu, which was declared a pandemic by the WHO in 2009, as well as historic waves of plague and cholera.

Spiteri added that the risk of hantaviruses to the general population in Europe remains low.

“Widespread transmission is not expected. Any transmission is likely to remain limited due to the close contact required and the infection prevention and control measures in place,” Spiteri said.

“Transmission is normally through rodents while person-to-person spread occurs only in rare close-contact situations. As the natural reservoir is absent in Europe, rodent-to-human transmission is not expected.”

“People shouldn’t panic since human-to-human transmission is so rare that a pandemic is impossible,” Strandin said.

He added that the long incubation period of the virus also allows more time to quarantine exposed individuals and virus spread can be efficiently controlled.