Seven people aboard a cruise ship may have contracted hantavirus, a deadly illness more often associated with inhaling dust from deserts or other lands. How could this have happened?
When ship outbreaks make headlines, the culprit tends to be norovirus or the virus that causes COVID-19. But now the cruise ship MV Hondius is moored off the coast of Cape Verde in Africa with sick passengers and crew on board. Hantavirus, a group of viruses that sometimes infects people who breathe in rodent droppings, may have killed three people and sickened four others.
The risk to the general public is low, Maria Van Kerkhove, director of epidemic and pandemic preparedness and prevention at the World Health Organization, said at a May 4 press conference. Contact tracing, laboratory testing and other work are underway, she said. “Our priority is to ensure the safety and health of passengers and crew while limiting the spread of this virus.”
Hantavirus was confirmed in two passengers. One, a British citizen who was evacuated to South Africawas the first to positive test for hantavirusaccording to Oceanwide Expeditions, the company that manages the cruise line. On May 5, the WHO confirmed that one of the deceased passengers, a 69-year-old Dutch woman whose husband died first on board, was also infected. Another person had a slight fever but now has no symptoms, Van Kerkhove said at a press briefing on May 5. This person is considered a suspected case, bringing the count to seven.
WHO is working with several countries to investigate the situation and evacuate sick passengers and crew members for treatment. The ship will continue to the Spanish Canary Islands where health authorities will conduct a thorough investigation and disinfect the ship.
Hantaviruses infect thousands of people around the world every year, sometimes with fatal consequences. Most cases go unnoticed, but some, like the death of actor Gene Hackman’s wife, Betsy Arakawa, and this cruise ship incident attract attention.
“When these viruses make waves, they make big waves,” says Sabra Klein, a viral immunologist at the Johns Hopkins Bloomberg School of Public Health. The reason hantaviruses “are making headlines is not because there are an incredible number of cases,” she says. “It’s still very rare, but we don’t have a vaccine, we don’t have a cure.” And mortality rates can be high.
Many questions remain about how cruise ship passengers fell victim to a virus that usually infects people on land. Scientific news I reached out to experts to answer some of them.
What is hantavirus?
Hantavirus is not just one thing. There are more than 50 different types of hantavirus, Klein says. Some can infect humans, even though humans are not the viruses’ usual hosts.
Hantaviruses infect rodents, moles and some bats, says Kartik Chandran, a virologist at the Albert Einstein College of Medicine in New York. The type of hantavirus aboard the cruise ship may be the Andes strain, a type of hantavirus found in Argentina, where the ship began its Atlantic cruise.
A type of hantavirus known as Seoul virus has spread around the world because it infects Norway rats which, despite their name, are ubiquitous. In the United States, clusters of hantavirus infections have been linked to the exotic pet trade. But, Chandran says, “most hantaviruses just go about their business and don’t infect people.”
Most hantaviruses have evolved to only infect specific host species, he says. Animals infected with the virus often do not become ill. And many people can be exposed to viruses but fight them off without getting sick.
How do people get hantavirus?
The urine, feces and saliva of infected animals contain hantavirus. Although people can catch it through saliva, most often they contract hantavirus when they breathe in aerosolized particles from rodent pee or poop, Chandran says. “These are accidental or zoonotic infections, meaning the virus jumps across the species barrier to humans.”
Hantavirus particles can be stirred up by “sweeping, vacuuming, all the things we think of when we see rodent droppings,” Klein says. Crew members are “probably vacuuming every nook and cranny of a ship,” but that could release even more viruses into the air. Use bleach or alcohol-based solutions to clean up rodent droppings and prevent aerosolization of the virus, she recommends.
How does hantavirus infect cells?
Hantaviruses are a group of viruses whose genetic material contains RNA. They are enveloped viruses: a hard protein envelope surrounds the RNA. This shell, in turn, is enclosed in a membrane studded with glycoproteins – proteins to which specific sugars are attached. These glycoproteins cluster in groups of four, giving the appearance of a virus covered in flowers, Chandran explains.
When a person breathes in the hantavirus, these flower-shaped complexes act like a machine to grab a protein on human cells called protocadherin-1, or PCDH1. Once attached, the cell engulfs the virus and takes it into a stomach-like compartment called the endosome. Just like when people eat food, a cell that has swallowed a virus receives a rush of acid into its “stomach.” Acidification is the signal given to the virus to let its flowers bloom very spectacularly, explains Chandran.
Glycoprotein is a multifunctional machine, a bit like a Swiss army knife, he says. Until acidification occurs, the knife is closed. But then, “like a Swiss army knife, it exposes the blade, and it sticks into the membrane of the cell. And then, just like a Swiss army knife, it exposes another blade.” Finally, he says, “this glycoprotein essentially fuses the membrane of the virus with the membrane of the cell, a bit like two soap bubbles coming together.”
This fusion releases the virus’s genetic material into the cell. The virus’s RNA acts “like malicious code inserted into a computer that redirects the cell to stop doing what it’s doing and turns it into a zombie that just creates new viruses.”
Can people pass hantavirus infections to each other?
Yes, but very rarely, and only with the Andean version of the virus, hantavirus, explains Michelle Haby, an epidemiologist at the University of Sonora in Mexico.
Haby and colleagues revised reports in which people are believed to have infected each other and has only found strong evidence in a few cases in Chile and Argentina. “Proving human-to-human transmission is very difficult because you also have to rule out the same environmental exposure to rodents,” she says.
A study in Chile found that of 476 household contacts of patients who contracted hantavirus, only 16 developed hantavirus pulmonary syndrome – a severe form of the disease – and had antibodies against the virus. In most of these cases, people were likely exposed to the same source of the virus. Only three cases are suitable for person-to-person spread. And it wasn’t just people living in the same house, Haby says.
“It was only with very, very close contact,” she said. ” To kiss [and] sexual contact was most likely.
Person-to-person spread on the ship is unlikely, Haby says. “Obviously, if the disease is extremely contagious, if there was easy person-to-person transmission, you would expect there to be a lot more people sick right now, and that’s clearly not the case.”
Passengers isolate themselves in their cabins and those on board wear masks and other protective equipment to prevent infection, Van Kerkhove said.
What happens when a person is infected with hantavirus?
Initial infection symptoms may include fever, chills, headache, nausea, stomach pain, vomiting, and diarrhea.
Once in the lungs, the virus can cause serious illness, partly because of its own action and partly because the immune system’s reactions to infection can damage delicate lung tissue, Chandran says. “These viruses are a bit like a burglar trying to rob a mansion he doesn’t know, and he cuts the wire to disable the alarm system, and instead the whole house explodes.”
New World hantaviruses in the Americas can cause hantavirus pulmonary syndrome, a serious respiratory illness. Symptoms include fever, cough and shortness of breath and can lead to respiratory failure and death. Until 35 percent people who develop serious lung disease die.
Old World hantaviruses in Europe and Asia can cause hemorrhagic fever with renal syndrome, which can lead to internal bleeding, low blood pressure, and kidney failure. Mortality rates for hemorrhagic fever range from less than 1 percent to 12 percent, depending on the virus.
Not everyone exposed to hantavirus will get sick, and many sick people will recover with treatment of symptoms, Klein says. “Anyone can be exposed. Anyone can get sick, but when you look at mortality patterns, it tends to be older people, who have other comorbidities that we know are associated with more severe respiratory illnesses.”
How did hantavirus get on a cruise ship?
Rats. Or other rodents.
There are two likely scenarios. In one, “there are probably infected rats on the ship, and the feces are on the ship, and the virus is aerosolized from the feces,” Klein says. It wouldn’t be the first time that infected rodents have carried disease aboard a ship, she said. “They go where the food is.”
In the other case, rodents were almost certainly involved, but the cases may not have been They were contracted while on board the ship, Chandran explains. It takes one to eight weeks after exposure for people to become ill from hantavirus. This is in the period from when the ship left Argentina about three weeks ago. “There have probably been people exposed on land in Argentina, where these viruses are endemic, and who have already adhered to the virus,” he says. “There’s a lot of detective work to be done to really understand what happened.”
Haby also questions the exhibition before departure. “I would like to know where they went in Argentina before boarding the cruise ship, because it is very possible that this is still consistent with a land-based infection,” she says. “We can’t even tell yet…the rats are on the ship.”
Van Kerkhove said the WHO is working on the assumption that the Dutch couple who died may have contracted the virus during a wildlife excursion in Argentina before joining the cruise. Other people may have come into contact with rodents on other islands or perhaps on board.
“However, we believe there could be human-to-human transmission between very, very close contacts: husband and wife, people who shared cabins, etc.… Our hypothesis is that this has occurred.”
