As public health officials around the world monitor dozens of former MV passengers and crew Hondius To detect signs of hantavirus infection, scientists hope to learn more about the mysterious and sometimes deadly virus causing the outbreak.
This virus has been confirmed to be the Andean hantavirus species, the only documented hantavirus spreading from person to person. Evidence so far suggests that the outbreak aboard the ship occurred when one or two people became infected on land and then transmitted the hantavirus to others on board. As of May 13, the outbreak had sickened at least 11 people, killing three.
Scientists are still trying to decipher what makes Andes virus different from other hantaviruses. Mysteries include why and how this disease can spread between humans, and why it can be so deadly. The answers may depend as much on the people infected and the circumstances as on the virus, researchers say.
Many different species and variants of hantavirus have been discovered. And thousands of people are infected every year around the world. Typically, these cases come from people breathing in dried rodent droppings. A rodent commonly known as the long-tailed colilargo or long-tailed pygmy rice rat (Oligoryzomys longicaudatus) carries the Andes virus.
These exposures often occur in rural areas and strike campers, people working outdoors, or those disturbing rodent-infested areas.
But in Chile and Argentina, researchers have already documented cases in which people were infected with Andean hantavirus from other people. birthday parties and wakes up, in hospitalson car trips and within households. And now, for the first time, at sea. A bird-watching trip near a landfill in Argentina reportedly led to the first two cases on board the ship – a Dutch couple who both died.
Proximity is next to contagiousness
Usually, person-to-person spread of Andes virus occurs among close contacts. Close means people exchanging spit – transmission is more likely between sexual partners and those engaging in sexual activity. deep kisses. Close contacts may also be those who spend extended periods of time together or health care workers who care for patients infected with hantavirus.
But as the ship and other examples illustrate, not everyone who catches the Andes virus is a close contact. For example, researchers carefully pieced together how an Andes virus outbreak in Argentina from November 2018 to February 2019 infected 34 people and killed 11. Four waves of infection were driven primarily by three super-spreadersthe researchers reported in the New England Journal of Medicine in 2020. These three people transmitted the virus to 21 other people. Some spread has occurred through casual contact, says Gustavo Palacios, a virologist at the Icahn School of Medicine at Mount Sinai in New York.
Palacios was part of a team that studied how properties of the virus and other factors contributed to the outbreak. The team found “some cases where we cannot demonstrate very close contact, as described by the transmission of fluids like saliva, semen or blood,” he says. “The only fluid they could have transmitted is respiratory secretions,” expelling airborne particles that others can inhale, much like the transmission of other respiratory viruses.
Monitor symptoms
A dozen countries are monitoring passengers and crew members who disembarked or were evacuated along the ship’s route, as well as people who came into contact with infected or exposed passengers on air flights or in other close-quarters situations. It can take up to six weeks for symptoms to appear after being infected with Andes virus.
As of May 13, laboratory tests had confirmed nine infections, according to the World Health Organization. The Andean virus is also suspected in two other cases: the Dutchman who died on board the Hondius on April 11 (no samples were taken because no hantavirus was suspected at the time) and a hospitalized British national who landed on the island of Tristan da Cunha in the South Atlantic on April 14. The island is so isolated that British paratroopers, some with medical personnel jumping in tandem, had to skydiving with medical supplies and oxygen to treat the man.
Not included in the WHO count American citizen tested positive and another who developed mild symptoms during a special medical repatriation flight from the island of Tenerife, US authorities announced on May 10. Eighteen U.S. citizens from the cruise are being monitored or treated for illness in quarantine and biocontainment units in Omaha, Neb. and Atlanta.
Seven other ship passengers are quarantining at home in five states. These are people who were on the Hondius when the first case died but disembarked before anyone realized hantavirus was on board. And 11 other Americans who sat next to a sick cruise passenger on airline flights are also quarantining at home.
For example, a man briefly attended a birthday party where he sat at a different table than the infected person who started the outbreak. “He didn’t stay there for a long time. He got infected while saying hello while he was going to the bathroom,” Palacios says.
This does not mean that the Andes virus is as infectious as respiratory viruses like the flu or the coronavirus that causes COVID-19. The person who spread the Andes virus at that birthday party infected only five people at the large party attended by more than 100 people, four of whom sat next to or near him, says Jonas Klingström, a virologist and immunologist at Linköping University in Sweden. “It seems that under certain conditions people shed viruses more easily than under normal conditions, but this is very, very rare.” Still, these rare cases make the case for isolating people exposed to the virus because, he says, “you can never predict who will spread the virus, because it doesn’t seem to have any relationship to the severity of your illness.”
No idea in the genes
Why the Andes virus can sometimes pass from person to person is not obvious from its genetic material. A some small adjustments in the Andes, the virus’s RNA appears to be associated with person-to-person spread, researchers reported in mSphere in 2023. The genetic makeup of Andes virus isolated from a Swiss passenger on the cruise ship is a virus genetically close to a virus involved in person-to-person spread described in this earlier study.
Analysis of viral RNA from the Swiss passenger places the Andean virus in the epidemic as a close relative of the Andean viruses of Chile and northern Argentina. The pygmy rice rat is common in these areas. Argentine authorities dispute that the outbreak started at the landfill, pointing out that rodents do not live in the Tierra del Fuego region of southern Argentina where the Dutch couple joined the cruise and that region has never had a human case of hantavirus.
The changes identified in Andean viruses transmitted between humans do not change the virus’s ability to reproduce, Palacios says. The virus also did not change much between the start and end of the Argentine outbreak and was no different among the super-spreaders.
If there is nothing special about the genetic makeup of the Andes virus, this could mean that other hantaviruses are capable of spreading among humans if the opportunity arises. “So, you know, maybe it’s not about the Andes, and every [hantavirus] who is on a rat in a port in any part of the world is actually capable of doing the same thing,” says Palacios.
Other experts doubt that human-to-human transmission has occurred with hantaviruses such as the Puumala virus or Hantaan virus in Europe and Asia or the Sin Numéro virus in the United States. People contract these viruses fairly regularly through contact with rodent droppings, but no one has documented person-to-person spread. Yet many species of rodents carry hantaviruses with unknown capabilities, Palacios says.
One reason Andes virus can spread among humans is that it reaches higher levels in humans than other types of hantavirus. Nobody knows why. Once the Andes virus has established itself in the bloodstream, “there’s virus everywhere. I mean, people are expelling the virus,” says Kartik Chandran, a virologist at the Albert Einstein College of Medicine in New York. “It’s in the kidneys. It’s in the lungs. With Andes, it’s in the oral secretions.”
Klingström and his colleagues also discovered that the Andes virus can resist antimicrobial compounds in human saliva which kill other hantaviruses, even though it is susceptible to other methods of killing it. Like other hantaviruses, “if we inactivate it with ethanol or something else, it’s very easy to kill,” he says. “Also, this virus is extremely sensitive to soap and light,” so this doesn’t seem to be any different.
Perhaps, however, the proteins are arranged differently on the surface of the Andes virus, making it more resistant to saliva. No one has identified why the Andes are more stable in saliva, but this property may partly explain human-to-human spread.
Andes virus RNA has also been found in other human bodily fluids, including blood, breast milk and sperm. In one case, a man who had recovered from a severe Andean virus infection still had Viral RNA in his sperm 71 months laterresearchers reported in Virus in 2023. He does not appear to have been contagious after his symptoms disappeared and detect viral RNA does not always mean that viruses are created.
The human point of view
The characteristics of people who contract Andes virus may be as important as those of the virus in determining infection. Superspreaders tend to produce many more viruses than others, Palacios and his colleagues found. And their livers and kidneys were more affected than people who did not transmit the virus or who transmitted it to fewer people.
Timing was also important, Palacios says. People were most contagious two days before symptoms appeared until two days after. Those who build antibodies against the virus early may shed less virus than those who take longer to produce antibodies, Klingström says.
Behavior can also play a role. “If you’re homesick, you’re probably not going to give it to anyone, or maybe you’ll give it to just one person,” Chandran says. But people who attend parties or go to a crowded movie theater can spread the virus to more people during the short period when they are most contagious.
The interaction between the virus and the immune systems of the people it infects can affect those who become seriously ill or die, Klingström says. People whose bodies produce high levels of an inflammation-triggering protein called IL-6 tended to have more severe symptoms with Andes virus than people who produced less IL-6, researchers reported in 2017 in Tropical diseases neglected by PLOS. Andes, like other hantaviruses, also prevents immune cells called T cells from attacking the virus, Klingström explains. It’s unclear whether Andes is particularly good at this.
Scientists still have a lot of work to do to determine why the Andes virus is able to transmit sustainably from human to human, Chandran says. “We currently have no data on why the Andes are special, or even if they are special,” he says. However, “there are so many cases of Puumala and Hantaan [hantavirus infections] that I think if there had been human-to-human spread, I think we would have seen it and caught it… So there’s clearly something different in the Andes.
