In 2018, health authorities in southern Argentina were racing, trying to understand what had caused nearly three dozen people in the tiny village of Epuyen to fall gravely ill. By the end of the outbreak, 11 of them had died.

Their illness, which caused many to be admitted to intensive care for pneumonia and severe breathing problems, was caused by the Andes virus, a strain of rodent-carried hantavirus capable of being transmitted from person to person. It is the same virus that’s believed to have sickened eight passengers traveling on the MV Hondius cruise ship, which is sailing to a port in the Canary Islands.

A United States citizen who was on the hantavirus-hit MV Hondius cruise ship is the latest to test positive for the virus while a French traveller has developed symptoms as the ship is being evacuated and passengers are returning to their home countries.

Passengers began flying home on military and government planes after the ship anchored near Tenerife, the largest of Spain’s Canary Islands, on Sunday.

At least eight people who were on board the ship had earlier been confirmed or were suspected of having contracted the hantavirus. Three people have died while at least one person is in intensive care.

Previously, officials from the Spanish Ministry of Health, the World Health Organization (WHO) and the cruise company Oceanwide Expeditions had said none of the more than 140 people who had been on board the MV Hondius was showing symptoms of the virus, but that has since changed.

As passengers are being flown home for testing and monitoring, health officials are racing to determine where and how the outbreak may have started.

There are no conclusive answers yet, but the trail has led investigators to Argentina, from which the MV Hondius departed on April 1.

Where did the hantavirus outbreak start, and where has it spread?:

Hantavirus infects humans who breathe in air contaminated with virus particles from infected rodents’ urine, droppings or saliva.

The current outbreak is linked to the Andes strain, which is endemic in rural parts of South America. It is the only form known to spread between humans.

It is not yet known where the initial contamination took place. Health officials are currently tracing the outbreak in Argentina, from which the ship departed.

The first people to develop symptoms were an elderly Dutch couple on the cruise ship, and they are among the three fatalities. It is not known if they were the first to contract hantavirus, however.

Local media in Argentina reported that the couple had visited a landfill site in Ushuaia, a popular tourist spot in southern Argentina’s Patagonia region, in search of a rare bird. There has been speculation that one person in the couple could have been exposed to rodent droppings there.

However, local health officials in Ushuaia said this is unlikely, telling reporters that the area has not recorded a hantavirus case since 1996.

However, some experts said examinations in the area are required to be certain of this because sometimes ecosystems change and vectors can move locations.

The resulting negative attention on Ushuaia has cast a shadow on local businesses, according to local media reports. The city is considered the “gateway to Antarctica” with most shipping expeditions departing from there. There is now a concern that the outbreak could reduce tourist numbers.

Last week, Argentinian health officials were deployed to the site with plans to take samples of rats in the area of the landfill and examine them for hantavirus.

Where else could the virus have come from?

There have also been suggestions that the couple, who had been travelling in the region for several months, may have been exposed to the virus in Chile or in other parts of Argentina where the Andean strain is endemic.

Argentinian media have reported that the couple arrived in Argentina on November 27. They then crossed into southern Chile and went on to Uruguay by car and remained there from March 13 to 27 when they returned to Argentina.

Hantavirus is endemic across most of Chile except in the country’s far north. The Andes strain, in particular, is endemic in Chile’s Aysen region. Chile shares a long border with Argentina.

The last similar transmission of the hantavirus from human to human was recorded in Chile in 2019.

Five Things To Know About Hantavirus From (Stanford University):

1. Hantavirus mostly infects wild rodents:–

Hantavirus is a zoonotic infection, meaning it originates in animals but can cause disease in humans. Hantavirus has been detected in more than 100 species of mammals, including foxes and bats, but is primarily found in wild rodents, which can have persistent hantavirus infections without symptoms. In one recent study, about 3% of deer mice and white-footed mice across the United States tested positive for hantavirus, with geographic hotspots in Virginia, Colorado and Texas.

People typically become infected with the virus by inhaling microscopic particles from these rodents’ urine, feces or saliva — for instance, while cleaning a remote cabin infested with wild rodents. In the last 30 years, the CDC has logged 890 cases of hantavirus disease in humans, with 94% of cases west of the Mississippi and most occurring in Colorado, Arizona or New Mexico.

Salinas was quick to point out that even in these high-risk states, house mice — the species you might see scurrying around a suburban garage or attic — are not the usual carriers of hantavirus.

2. This outbreak strain is unusual in its ability to spread between people:–

Hantavirus strains found in North America, including the strain that most likely killed Betsy Arakawa, don’t spread from person to person. Someone may become infected from rodents, but the virus ends there. The Andes virus, found in South America, is different; it is the only hantavirus documented to occasionally transmit between people. In 2018, the Andes strain of hantavirus spread throughout a small village in Argentina. Ultimately, the virus infected 34 people and caused 11 deaths.

But hantavirus, even the Andes strain, is not efficient at spreading between people.

“There are respiratory viruses like flu and COVID-19 that are incredibly efficient at transmitting person to person. That’s what they have evolved to do,” Salinas said. “Hantavirus just isn’t like that. It can jump to a few people after close contact with an infected, symptomatic individual, but we don’t expect it to spread very far.”

Data suggests that transmission between people requires close contact with someone who is already showing signs of infection. An analysis of the 2018 outbreak found that it began when one person, infected from a rodent, attended a birthday party of about 100 people. Over the following months, just three symptomatic individuals — attending other social gatherings while ill — drove all 34 infections.

In the end, the 2018 outbreak was contained through isolation and quarantine. More than 80 health care workers who had unprotected contact with patients were not infected, underscoring how inefficiently the Andes virus tends to jump between humans.

3. The disease can be deadly, and there is no vaccine:–

Rare as it is, hantavirus is not something to take lightly; its fatality rate is much higher than more common viruses such as influenza and COVID-19. Thirty-five percent of hantavirus cases in the U.S. in recent decades have led to death.

Early symptoms of hantavirus pulmonary syndrome — including fever, fatigue and muscle aches — show up anywhere from 4 to 42 days after exposure and might be mistaken for the flu. But symptoms can rapidly progress to severe pneumonia and respiratory distress.

Researchers don’t fully understand how the virus causes such damage. Like the most severe COVID-19 cases, deaths from hantavirus may be due to an overactive immune response.

“It clearly affects the lungs,” Salinas said. “But it’s not clear how much of that is the virus attacking the lung cells versus the response of our body to the infection.”

There are no approved vaccines and no specific antiviral therapies proven effective against hantavirus. Patients who become sick can receive supplemental oxygen; mechanical ventilation; or, in the most severe cases, extracorporeal membrane oxygenation (ECMO), a machine that takes over the work of the heart and lungs while the body fights the infection.

“Because this virus is so rare, there just hasn’t been a whole lot of research into it,” Salinas said.

Data is sparse, for instance, on whether some groups of people — such as young children or elderly adults — are more likely to become severely ill, or whether some people are more likely to spread the virus.

4. Travel risk is negligible, but an N95 is smart in certain situations:–

Cruise ships and airplanes are not, under normal circumstances, places where anyone would expect to encounter hantavirus.

“If you asked me last month, I wouldn’t have predicted that we would see this on a cruise ship,” Salinas said. “I would still say that your risk of acquiring this particular rare infection on a plane or ship is very, very low.”

The outbreak required a specific and unlikely chain of events: A passenger had to be exposed to an infected rodent in Argentina, then board a ship where close quarters allowed the virus to spread. Salinas doesn’t expect that chain to repeat itself.

“Your risk of acquiring something else on a cruise is much higher,” he pointed out.

The picture looks slightly different for those heading into wilderness areas in the Western United States, where hantavirus circulates in wild rodent populations. If you’re planning on spending time in enclosed spaces where rodents may have nested — old cabins or hiking shelters, for instance — be mindful of disturbing rodent feces. If you’re sweeping out an area like this, Salinas recommended opening windows and wearing an N95 respirator — available at most hardware stores.

“It’s always a good thing to do in those situations,” he said, noting that the precaution guards against other diseases, not just hantavirus.

5. Hantavirus is part of a larger pattern:–

The list of diseases that have jumped from animals to humans — including hantavirus, Ebola, avian influenza and COVID-19 — grows longer every year. About three-quarters of all emerging infectious diseases are zoonotic, and scientists expect that number to increase. That’s in part because humans are pushing deeper into wildlife habitats than in the past and because climate change is reshaping where animals live and breed.

“Given the way the world keeps changing and our populations are growing and moving, viruses will keep leaping from animals to humans,” Salinas said. “I expect this hantavirus outbreak to end, but it won’t be the last, and it’s a reminder that outbreaks can occur in unpredictable locations.”

Salinas sees the MV Hondius outbreak as a warning — and a reminder that we are never fully prepared for the next outbreak. The challenge, he said, is that the rarity of diseases like hantavirus has made them a low priority for research investment, leaving clinicians with no treatments or vaccines when outbreaks do occur.

“We should be investigating these diseases,” Salinas said. “That means investing in surveillance, in research, in understanding how these viruses move through animal populations before they reach us.”

Hantavirus Explained: What To Know After The Cruise Ship Outbreak (Harvard University):

What is hantavirus?:–

This class of virus was first identified in the Hantaan River area in Korea. Mice and other rodents often carry the hantavirus. Humans can contract the disease when they come into contact with infected rodents or their saliva, urine, and droppings.

Hantavirus was first recognized in the United States in 1993 (see “A mouse story”) and has since been identified throughout the country. Although rare, the disease is potentially deadly, especially if it involves the kidneys, heart, or lungs.

What are the symptoms of hantavirus?:–

Early symptoms of the disease include fatigue, fever, and muscle aches, especially in the large muscle groups – thighs, hips, back, and sometimes shoulders. About half of all people infected also experience headaches, dizziness, chills, and abdominal problems such as nausea, vomiting, diarrhea, and abdominal pain. Four to 10 days later, other symptoms may appear, including coughing and shortness of breath, as the lungs fill with fluid.