Why were cruise ship passengers sent home amid a deadly outbreak? Your hantavirus questions answered

Now that most of the passengers from a luxury cruise ship are back in their home countries after a deadly hantavirus outbreak was declared on board, questions and concerns about the illness continue to circulate.  

MV Hondius, the ship at the centre of a rare hantavirus outbreak, docked at Spain’s Canary Islands over the weekend, allowing passengers to disembark and be repatriated home. 

Four of those passengers are Canadian citizens who are currently self-isolating in B.C. Two others from Ontario, who disembarked at one of the ship’s earlier locations, are self-isolating after having returned home a few weeks ago. 

• What questions do you have about hantavirus? Send an email to ask@cbc.ca

Meanwhile, six other Canadians from Ontario (3), Alberta (2) and Quebec (1) who were not on the ship, but had come into contact with possible hantavirus cases, are also self-isolating and following public health measures. 

As of Monday, none of the Canadians have been tested and none are showing symptoms at this time, according to health officials.

CBC News put some of your most asked hantavirus questions to the experts. 

What is the most common hantavirus strain in Canada? 

The most common strain of hantavirus in Canada is called Sin Nombre. 

Dr. David Safronetz, chief of special pathogens at Canada’s National Microbiology Laboratory, said the Andes strain hasn’t circulated in Canada and, at this time, experts don’t believe it will.

“We simply do not have the rodent reservoirs that maintain Andes virus in the natural environment,” said Safronetz. Canada’s cold winters also likely prevents the virus from establishing roots here, he added. 

The Sin Nombre strain is slightly different from Andes in that it doesn’t spread between people, according to Safronetz, but it still causes a severe respiratory illness. 

WATCH | What is hantavirus?:

At least three people are dead and three more are sick as of May 4 in what the World Health Organization says is a suspected outbreak of hantavirus aboard a cruise ship. The WHO has confirmed at least one case aboard the MV Hondius and that passenger has been airlifted to a hospital in South Africa.

It also has a high death rate of about 30 to 40 per cent, he said. 

The overall risk in Canada remains low, with just under 170 cases of hantavirus pulmonary syndrome reported in the country since surveillance started in the 1990s. 

Which rodents carry hantavirus in Canada? 

The three common rodents known to carry hantavirus in Canada are: the deer mouse, the white-footed mouse and the red-backed vole. These species tend to live in more rural areas that are either wooded or open fields. 

A 2020 report shows that many cases of hantavirus pulmonary syndrome were in the Prairies, with Alberta reporting the highest number.

If your area is contaminated by rodent droppings, experts say you should take care to properly clean and disinfect it. That includes wearing gloves and masks while you clean, and not sweeping or vacuuming rodent droppings. 

How does hantavirus spread between humans? 

Since there’s been limited human-to-human spread of the Andes hantavirus, it’s not fully known how it spreads between people. 

But experts say that in most cases the virus has jumped between people who have been in close and prolonged contact. 

“The [World Health Organization] is suggesting within two metres for 10 to 15 minutes at least,” said Safronetz. 

WATCH | Doctor explains what you need to know about the hantavirus:

Hantavirus spread: Doctor explains what you need to know

As Canadian passengers from the hantavirus-hit MV Hondius cruise ship are back home isolating, there are concerns about a potential spread of the illness. For The National, Erica Johnson puts viewers’ questions to infectious diseases specialist Dr. Lynora Saxinger.

According to infectious disease specialist Dr. Lynora Saxinger, who spoke with CBC’s The National, people infected with the Andes strain spread it through, “speaking, singing, coughing, oral secretion sharing,” such as kissing.

“It’s not the same as something like measles or even something like influenza, where you expect that the whole airspace might be contaminated — there does seem to be an intensity of contact and a duration of contact,” she said. 

But someone who has higher amounts of the virus in their saliva, might also be able to more easily spread the virus, says Saxinger. That means even short contact could pose a risk. 

How long should suspected cases isolate for?

According to B.C. health authorities, the four Canadians who landed in the province will begin a three-week isolation period. That might be extended up to 42 days if necessary, due to the hantavirus’s incubation period. 

Their self-isolation technically began on the ship in early May, after the hantavirus outbreak was confirmed. 

Dr. Gerald Evans, medical director of infection, prevention and control at Kingston Health Sciences Centre in Ontario, told CBC News that the isolation guidance given to each Canadian involved in this situation is likely based on when public health officials believe they were first exposed. 

He added that while it could take eight weeks for symptoms to show, based on the data, a “vast majority” of people will have symptoms within a 30-day window.

Why were the passengers let off the ship? 

Experts say the decision to send people on the ship back home was likely driven by a lack of medical resources on the ship. 

“If people aboard the cruise ship were to fall ill, they would need to be evacuated to somewhere that could actually provide them with the appropriate medical care. So in that sense, isolating on a cruise ship from a medical perspective doesn’t really fit with the severity of this disease,” said Safronetz, chief of special pathogens at Canada’s National Microbiology Lab. 

Can positive, asymptomatic cases spread the virus? 

If someone tests positive and is asymptomatic, they might be able to spread the virus, but it’s highly unlikely, according to Bryce Warner, principal scientist at the vaccine and infectious disease organization at the University of Saskatchewan.  

“If you’re feeling healthy and you don’t have any clinical signs or symptoms, we think that the risk is quite low during that period,” he said. 

But some evidence shows that transmission can happen about 48 hours before someone shows symptoms, he said. 

“If you are infected, once you start to creep toward that symptomatic period, that’s really when the virus is sort of at its symptomatic peak, so that’s why the risk sort of increases around that time window.” 

How do we test for hantavirus?

Health officials in Canada have said they are not testing the passengers who are isolating here, because without symptoms, test results won’t be accurate. 

But some countries are approaching this differently, with experts in the United States saying they plan to test on a case-by-case basis.

So far, one asymptomatic American has tested positive. 

The two ways to test would be through a PCR (polymerase chain reaction) test or a serology (blood) test. 

A positive serology test indicates a build up of antibodies, suggesting an immune response to the virus, Warner says. That could mean that they had or currently have the virus. 

Meanwhile, he says a positive PCR test would suggest that the person currently has the illness as it detects whether the virus itself is present. But in the early weeks of getting infected, when the viral load in your body is low, the test might not detect it and come back falsely negative. 

“If someone has a confirmed case that means they probably … had one or both of those come up positive,” said Warner. 

Can you get hantavirus from your pet? 

If your pet is a rodent, then yes, says Safronetz. 

He said there have been documented cases where people with pet rodents were infected with a certain type of hantavirus strain. 

As for whether you can get hantavirus from your cat or dog, Safronetz says even if your pet is exposed to the virus, there’s no evidence showing that they can become infected or transmit it. 

But if you have a pet that likes to hunt rodents, you should beware, he said. 

“I would say though as a caution to pet owners, particularly [to] cats that like to hunt mice as trophies and present them to their owners as little gifts, cleaning up those dead rodents could present a risk,” he said. He suggests people take proper precautions when disposing of those rodents.