As 41 Americans across 16 states are now being monitored for hantavirus symptoms following the deadly outbreak on the MV Hondius cruise ship, panic has spread across the US.

But this isn't the first time that a rat virus outbreak has sparked hysteria.

In summer 2012 a homegrown plague at one of the country's most beautiful hiking spots sickened 10 visitors, left three of them dead and sparked a mammoth outreach effort to contact more than a quarter of a million guests who has stayed in the epicenter of the outbreak.

The virus swept through Curry Village, a cluster of canvas-sided cabins near Half Dome in Yosemite National Park, in August 2012.

The strain that hit Yosemite was called Sin Nombre, which is not transmitted through person-to-person contact like the cruise ship strain, but through direct inhalation of rodent droppings. The Andes strain, one of the rarest, has been blamed for the outbreak on the MV Hondius and can spread through person-to-person contact, with a staggering 40 percent fatality rate.

A National Institutes of Health (NIH) report revealed findings of an investigation into the Yosemite outbreak that looked at how the virus at the park may have spread, how prevalent it was in the rodents there and what needed to be done to tackle potential future outbreaks.

The report stated that of the 10 patients, 'eight case-patients experienced hantavirus pulmonary syndrome, of whom five required intensive care with ventilatory support and three died. 

'Staying overnight in a signature tent cabin (nine case-patients) was significantly associated with becoming infected with hantavirus. 

'Rodent nests and tunnels were observed in the foam insulation of the cabin walls. Rodent trapping in the implicated area resulted in high trap success rate (51 percent), and antibodies reactive to Sin Nombre virus were detected in 10 (14 percent) of 73 captured deer mice.'  

Guest lodgings in Curry Village, at an elevation of 4,000ft above sea level, consisted of 319 regular tent cabins, 91 signature tent cabins, 18 standard hotel rooms, and 70 hard-sided wood cabins on 23 acres. 

The NIH report stated: 'Opportunities for mouse entry were also observed for both types of cabins. Regular tent cabins evaluated often had gaps between the door and threshold and gaps between the canvas and the frame or foundation. 

'Most signature tent cabins evaluated had gaps between the door and threshold, gaps between the outer canvas tent and inner insulated wall, and holes in the exterior walls or floors, particularly around conduits for heaters. 

'In late August 2012, when the cabins were being inspected and retrofitted to close these gaps, evidence of active rodent infestation (tunneling and nesting and live mice) was observed in the wall foam insulation of most signature tent cabins.' 

Authorities were faced with the difficult task of tracing all those who had stayed in the lodging and at the park.

The report stated: 'During August 27 - September 17, 2012, Yosemite contacted 10,000 guests who had stayed in signature tent cabins, 30,000 who had stayed in regular tent cabins, and 230,000 guests who had stayed in other park lodging, representing visitors from 77 different countries. 

'The Yosemite public hotline received more than 4,800 calls. Hantavirus educational materials were handed to every park visitor, and educational messages were posted in public areas, in lodgings, and on the park internet site.' 

After the outbreak all the signature tent cabins at Curry Village were closed and torn down. 

Infectious disease specialist Dr R Scott McClelland told Daily Mail that the Sin Nombre strain that broke out in Yosemite is the most common in the US. 

McClelland said in the camp setting, all hikers would have had to have been exposed to mouse contaminated products.

'So basically to dust or what have you that's contaminated with mouse feces and saliva and urine.

'And if you've got a big mouse infestation and the mice are carrying hantavirus, it's pretty easy to spread to a number of people that way,' he added.

McClelland explained that rodents can spread the hantavirus like wildfire as they have 'high virus loads.'

'What you would probably have is a whole colony of mice, you know, living in a rustic abandoned cabin or in a grain elevator that's not currently in use and a ton of food and nesting spots for mice. And they're all probably infected with it,' he said.

McClelland assured that the risk of Americans contracting the rat virus is extremely low. 

'When hikers have a risk it would really be from sleeping in some kind of a lean-to or rustic cabin or shelter that has a rodent infestation.

'And particularly for cleaning up a rodent infestation and people who are doing something like that, so agricultural workers cleaning out a grain silo in preparation for filling it or things like that, that's the bigger risk.

'It's recommended that folks with that kind of exposure use personal protective equipment to avoid inhaling the dust in an environment like that,' he added.  

The findings of the NIH report concluded: 'Continuous public awareness and rodent control and exclusion are key measures in minimizing the risk for hantavirus infection in areas inhabited by deer mice.'

The Yosemite outbreak was the last cluster case of hantavirus in the US. Between November 2018 and February 2019, a small Argentine village experienced an outbreak of the rare Andes strain, similar to the cruise ship, after an unknowingly infected person attended a birthday party, resulting in 11 deaths.

Following evacuation of the MV Hondius on May 10, World Health Organization (WHO) chief Tedros Adhanom Ghebreyesus said 'our work is not over' to contain the lethal virus.

'There is no sign that we are seeing the start of a larger outbreak,' Ghebreyesus told a joint news conference in Madrid with Spanish Prime Minister Pedro Sanchez.

'But of course the situation could change, and given the long incubation period of the virus, it's possible we might see more cases in the coming weeks,' Ghebreyesus said.

So far 10 people from the cruise ship have fallen sick from the virus including three who have died.

According to Dr Steven Quay, all generation-two cases – those involving people who developed symptoms after contact with 'patient zero', Leo Schilperoord, 70 – took an average of 22 days to become sick.

That means generation-three cases – involving anyone who contracts the infection from the passengers – should start showing up around May 19, if the same incubation period of approximately three weeks remains true, he said.

In previous outbreaks of the Andes strain, like in Argentina, the peak time for symptom onset was 22 to 28 days.

Before the outbreak was identified on the cruise ship, 29 passengers disembarked from the Hondius on Saint Helena on April 24 - the destination marking the end of the first leg of the trip.

Health authorities are rushing to identify any potential contact cases who may have contracted the virus from those who left the ship before the virus was identified.

According to the CDC, as of the end of 2023, 890 cases of hantavirus were reported in the United States since surveillance began in 1993.