What is hantavirus? Here's everything you need to know about how it spreads
Experts explain why the outbreak aboard a Dutch cruise ship is so rare—and how much of a risk it poses.
It’s not extraordinary for a cruise ship to be afflicted by an eruption of infectious diseases. But the recent cluster of hantavirus cases on the M.V. Hondius, a Dutch polar expedition vessel sailing from Argentina to the Canary Islands, was “definitely a surprise,” says Steven Bradfute, an immunologist and hantavirus researcher at the University of New Mexico Health Sciences Center.
Gastrointestinal infections like norovirus and E. coli are most common, although respiratory infections also sometimes cause onboard outbreaks, as when COVID-19 stranded the Grand Princess off the shores of California in the early days of the pandemic.
However, this is the first cruise ship-associated outbreak of hantavirus Bradfute says he has heard of, and its circumstances are concerning enough that public health officials are watching closely. On May 6, the World Health Organization announced that the virus involved in the cluster was an Andes virus.
So far, eight cases have been identified, including three deaths, one person who is critically ill, three who have mild symptoms, and a newly identified patient in Switzerland who had traveled on the ship. All but the newly identified patient developed symptoms between April 6 and 28 and experienced fever and gastrointestinal symptoms, with rapid progression to pneumonia, leading to cardiovascular collapse for some.
The ship remains stranded after it was refused permission to dock in Cape Verde, and its remaining passengers are confined to their cabins.
What is hantavirus and how does it spread among humans? Here’s everything you need to know.
What is hantavirus, and why is it rare?
Hantavirus is in the Hantaviridae family of viruses carried by rodents. The animals harbor the virus without becoming ill, then shed it in their urine, droppings, and saliva. When those secretions are disturbed—during cleaning, farming, or simply entering an infested space—the virus can become aerosolized and inhaled by a nearby human. The virus can also infect humans if they eat contaminated food, or touch a contaminated object and then their mouth.
More than 40 species of hantavirus exist in nature, and they’re broadly divided into two categories—Old World and New World. Old World hantaviruses are endemic in Europe and Asia and primarily cause bleeding disorders and kidney dysfunction. New World viruses are more prevalent in the Americas and more commonly cause pulmonary edema, a condition in which fluid accumulates in the lungs.
The consequences of infection can be severe, especially for infections with New World strains. Between 1 and 15 percent of infections lead to death in Asia and Europe, but about half of hantavirus cases in the Americas are fatal.
Infections are not evenly distributed around the world. Between 10,000 to 100,000 hantavirus infections are thought to occur each year, most of them in Asia and Europe. In the Americas, only 150 to 300 infections are reported annually, with Argentina, Brazil, Chile, and Bolivia typically accounting for the majority. Between 15 to 50 cases are identified annually in the US. The specific strain of hantavirus involved in a cluster of cases determines how deadly the infections are likely to be. It also has important implications on how experts think the virus is spreading, and what they must do to contain it.
How does a hantavirus spread to—and among—humans
When hantaviruses make the jump from animals into humans, it’s often in situations when contaminated urine, droppings, or nesting materials of an infected rodent get stirred up—for example, when someone is sweeping out a barn. However, people can also get infected with the virus when saliva, urine, or feces from an infected rodent gets into skin wounds or into a person’s eyes, nose, or mouth.
Most hantaviruses are not spread between humans. It’s unclear why, although in one laboratory study, the viruses appeared to produce very few mature virus particles in the lungs of infected humans.
The Andes virus is hantavirus’ one important exception. This New World virus is responsible for most of the cases recorded in Argentina, Chile, and Uruguay. Why this hantavirus strain can make the human-to-human jump while others cannot remains an open question. One line of research suggests Andes virus may be uniquely resistant to the antiviral components of human saliva that seem to neutralize other strains before they can spread.
Either way, Andes’ spread is not particularly efficient, says Bradfute. Unlike measles and Covid, which can be spread by viruses lingering in the air after an infected person has left a room, Andes virus is spread by close contact, he says. “So when you have people sleeping in the same bed, or sex partners, or people sharing food, the virus can transmit that way. But it doesn't transmit to huge groups of individuals,” he says.
A 2018–2019 outbreak in Argentina illustrated the possible fallout of Andes transmission. After one person contracted the infection from a rodent, three people who sat near them at a birthday party went on to attendcrowded social events, ultimately resulting in 34 infections and 11 deaths.
Several theories could explain how multiple people in one social group could get hantavirus infections at the same time. One is that a single infected person transmitted the infection to everyone else—a hypothesis that only makes sense if the Andes strain is involved.
Does the latest outbreak pose a risk?
In a May 5 press conference, Maria van Kerkhove, the World Health Organization’s head of epidemic and pandemic preparedness and prevention, said the risk of the virus to the general public is low. That’s largely because of the comparative inefficiency of hantaviruses—even the Andes strain—at spreading between humans, says Bradfute.
According to a recent publication he coauthored, around a quarter of randomly tested rodents in New Mexico are infected, but the state still sees only a handful of human hantavirus cases every year.
It “transmits rather poorly,” he says, “so even though they're dangerous viruses, they are not super widespread.”
