An outbreak of hantavirus aboard a cruise ship in the Atlantic Ocean has heightened concerns about the rare but deadly virus. Public health officials say that the threat to the general public remains low based on what we know about the virus and how it spreads.
The outbreak involves the Andes strain of the virus.
There are many different strains of hantavirus, said Dr. Gaby Frank, director of the Johns Hopkins Special Pathogens Center in Baltimore. Laboratory testing has shown that the cruise outbreak involves the Andes strain, which is endemic to South America, including Argentina, where the ship departed on April 1. Dr. Maria Van Kerkhove, head of epidemic and pandemic preparedness and prevention at the W.H.O., said the initial cases of hantavirus were in a couple believed to be infected before they boarded in Argentina.
Most forms of hantavirus spread through contact with the feces, urine and saliva of infected rodents, including when humans breathe in particles of the virus. The Andes virus is the only strain known to spread from human to human, though such cases are rare.
Unlike the flu, Covid or even the common cold, it’s exceedingly difficult for the Andes strain to move between people, said Bryce Warner, a research scientist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan who has extensively researched hantavirus.
The flu and Covid primarily spread from the upper respiratory tract and replicate in high levels. Hantavirus sheds less easily, and also burrows deep into the lungs and infects blood vessels. “It’s not very easy for the virus to get out,” Dr. Warner said.
Those at highest risk of person-to-person transmission are people who have been in close quarters for prolonged periods of time with someone who has been infected, like health care workers or those who share a household. Two of the passengers who died on the ship were a married couple. The ship’s doctor showed symptoms of the virus and was evacuated from the ship. It isn’t clear yet how other people on board may have been infected.
Dr. Van Kerkhove has said that some of the cases were in close contact with one another, and that “human-to-human transmission can’t be ruled out.”
Most passengers remain on the ship.
Health officials have not said how those on the ship may need to quarantine when they disembark. They might ask people who were exposed to the infected cases to quarantine, but it’s tricky to keep people isolated for an extended period of time, since it can take between one and six weeks after a person is exposed for symptoms to appear.
The W.H.O. said that health officials have initiated contact tracing for people who may have been exposed to people who left the ship, such as one woman who flew to South Africa for care and who later died.
Outside of this outbreak, the virus is dangerous, but rare.
In general, hantaviruses pose a small risk to the general population. There have been a total of 890 cases in the United States since surveillance began in 1993. The vast majority of these have been caused by the Sin Nombre strain of the virus and have occurred west of the Mississippi River, with case counts highest in New Mexico, Colorado, Arizona and California. Of these cases, 35 percent have been fatal.
The Andes virus is not endemic, or native, to the United States, though there have been imported cases from other countries, said Steven Bradfute, an associate professor at the University of New Mexico Health Sciences Center.
Both the Andes and Sin Nombre strains can cause hantavirus pulmonary syndrome, a condition that begins with flu-like symptoms such as fever and chills but can rapidly progress to lung problems and difficulty breathing. There is no drug that can treat the infection, so doctors can offer only supportive care, which might include oxygen or a heart-lung machine. Getting to a hospital quickly and receiving breathing support can improve the chances of survival.
Different strains of the virus circulate in Europe and Asia, where there are thousands of cases each year, but the lethality rate is lower, between less than 1 percent and 15 percent, depending on the strain. Those versions of the virus primarily affect the kidneys.
But researchers stressed that the average person should not worry about the virus or necessarily change their daily behavior.
“There’s really no risk to anyone who is not on that ship,” Dr. Warner said.
It’s very different from the early spread of Covid.
Reports of the outbreak might seem similar to the early days of the Covid pandemic, when a mysterious virus was spreading on cruise ships and passengers were being quarantined on board. But experts said that the hantavirus is much more difficult to transmit and has considerably less potential to turn into a pandemic.
“It’s good to be cautious, but there’s no need for concern over a global outbreak,” Dr. Bradfute said.
Dr. Emily Abdoler, a clinical associate professor of infectious diseases at Michigan Medicine, said that past cases of the virus spreading between humans had not resulted in large outbreaks — “nothing even close to the scale of Covid.”
Those at greatest risk can take steps to protect themselves.
Agricultural workers who come into contact with mice and rodent droppings are at increased risk. This time of year in the northern hemisphere, as people are cleaning sheds and garages that may have gone untouched over winter, they might want to be especially careful about mouse and rodent droppings.
You can wear gloves and use a bleach solution or a household cleaner to wet surfaces when cleaning them. Don’t sweep or use a vacuum, which could stir particles into the air that you could inhale. Wearing a well-fitting N95 mask can offer protection against viral particles, Dr. Bradfute said.
People who travel to places where the virus is common and visit rural areas or go camping or hiking should take precautions to minimize exposure to potentially infectious materials. The W.H.O. has a fact-sheet that describes where infections are most prevalent.
Nina Agrawal is a Times health reporter.
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