As investigations continue into the hantavirus outbreak that originated on the expedition cruise ship MV Hondius, concerns swirl about the prevalence of the virus in the U.S.

Among passengers of the ship, which was traveling from Argentina across the Atlantic, there have been three deaths and at least eight reported cases, several of them laboratory-confirmed, according to the World Health Organization and subsequent health reports.

At least five states are now monitoring residents who returned from the MV Hondius, including Texas, Virginia, Georgia, Arizona and California, reports have noted.

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In the U.S., there have historically been around 800 to 900 cases of hantavirus, according to Luis Marcos, M.D., professor of medicine and director of the Infectious Diseases Fellowship Program at Stony Brook Medicine in New York.

CDC data supports this, showing that 890 cases of hantavirus disease have been reported in the U.S. from 1993 through the end of 2023.

“Most of these cases have been west of the Mississippi River, and classically the risk factors are being in contact with feces and urine from rodents,” Marcos told Fox News Digital. 

The most common strain is called Sin Nombre, which is not transmitted from human to human, the doctor said.

“The transmission is not as efficient as other viruses.”

Most strains of hantavirus spread from inhaling contaminated particles from rodent urine, droppings or saliva – or, less commonly, from touching contaminated surfaces and then touching the mouth, nose or eyes – and are not transmitted person-to-person.

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Typical scenarios include people who have been camping or hiking in remote areas and were inadvertently in contact with these feces or urine.

“The only proven human-to-human transmission has been with the Andean virus from South America — and that’s what’s happening now,” Marcos told Fox News Digital.

The current cruise ship outbreak reportedly originated with a couple who contracted the virus while traveling in Argentina.

“They were not symptomatic at all — the incubation period can be one, two, three or four weeks,” Marcos said.

Most infected people become ill with symptoms that are similar to flu and COVID, such as fever and muscle pain.

“Some people may have mild disease, so not everybody will be very, very sick,” the doctor noted.

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In rare cases, hantavirus can lead to hantavirus pulmonary syndrome (HPS), which causes the lungs to fill with fluid and can be fatal, the doctor noted.

“The mortality rate [among those with HPS] is between 30% and 60% — so yes, it’s a deadly virus,” the doctor added.

In terms of transmission, Marcos emphasized that those at highest risk are the people in “close contact,” which typically means living in the same environment where fluids can be exchanged.

“The longest incubation period has been 56 days or so.”

“It has to be really, really close contact,” he said. “The transmission is not as efficient as other viruses.”

While it’s possible for the virus to be airborne via droplets, Marcos pointed out that those transmissions are “not as effective” as COVID, influenza or cold viruses. 

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“For this cruise, it’s important to have people in quarantine for a period of time,” he said. 

The virus has a long incubation period, which means the quarantine duration will likely be several weeks. “The longest incubation period has been 56 days or so, so two months, roughly,” Marcos said. “But most cases will get sick within two to three weeks.”

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There are not currently any antiviral treatments for hantavirus. 

“So what happens is the patient will end up in the hospital. We will do supportive care, which means if your lungs are full of fluid, you will require a ventilator until you know the virus runs its course,” Marcos said.

Although there is not currently a vaccine for hantavirus in the U.S., Marcos noted that several are in development.

The doctor said he believes the risk of hantavirus leading to a pandemic is “pretty much almost zero.”

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“I don’t feel a strong risk of a pandemic,” he told Fox News Digital. “The transmission is not like COVID. It’s very different.”

“I really think this is going to go away in the next two to three weeks, and we will know exactly the number of cases,” he added.

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To prevent hantavirus, Marcos recommends wearing gloves and a mask in environments where mice might be present, such as cleaning a basement. 

Proper ventilation and frequent hand-washing can also help curb spread.