Hantavirus testing might not be useful for people without symptoms: experts

TORONTO — Health experts said it’s not clear whether it’s useful to test people who may have been exposed to hantavirus but don’t have symptoms, which has been the case so far for people in Canada with connections to a hantavirus-stricken cruise.

Dr. Bonnie Henry, British Columbia’s provincial health officer, said public health officials around the world are discussing the issue as passengers from the ship have returned to their home countries.

She said tests for some viruses aren’t effective before patients develop symptoms and little is known about how well testing works in rare cases of hantavirus.

Henry said there are two types of blood tests for hantaviruses — one that checks for antibodies and a PCR test that detects pieces of the virus itself.

If any of the 10 people in Canada who may have been exposed to the virus develop symptoms, Henry says health officials are ready to test and treat them. So far, they all remain asymptomatic, according to their respective provinces of Ontario, Quebec, Alberta and B.C.

Alberta health officials said Tuesday their two travellers are self-isolating at home, and that their focus is on monitoring them. “If they display symptoms, testing will be conducted but, as noted, there have been zero symptoms to date,” said Tom McMillan, spokesperson for the Alberta Primary Health Ministry.

Vancouver Island health officials also said the four in their region are showing no symptoms, and that they are providing supplies to their respective places of isolation.

The only person in Canada connected to the outbreak who is no longer isolating is in Quebec, after the province’s health ministry said they were deemed a low risk contact.

University of Saskatchewan hantavirus scientist Bryce Warner said health officials are in a “unique” situation because doctors wouldn’t normally have any reason to suspect the rare virus until a patient is showing signs of illness.

Warner, who works at the university’s Vaccine and Infectious Disease Organization, said a negative test in someone without symptoms wouldn’t necessarily mean they don’t have hantavirus.

“Because the incubation period can be several weeks, if you did a test in the first week and it was negative by PCR you can’t just say ‘OK I’m negative.’ It could take another week or two or three really for that to come up as positive,” he said.

The number of positive cases internationally has grown since the evacuation of the MV Hondius ship Sunday on an island in Spain’s Canary Islands. On Tuesday, Spain’s health ministry announced that a passenger evacuated from the ship had tested positive for the virus.

American and French officials confirmed two more people had tested positive a day earlier. The American passenger tested positive but did not have symptoms and was being monitored in the Nebraska Biocontainment Unit, said Kayla Thomas, a spokesperson for the Nebraska Medicine hospital caring for passengers.

That brings the total number of deaths to three and cases to 11, all among passengers and crew, the director of the World Health Organization said Tuesday in Madrid. No additional deaths have been reported since May 2.

“At the moment, there is no sign that we are seeing the start of a larger outbreak. 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, ” Dr. Tedros Adhanom Ghebreyesus said.

Public health officials and infectious disease physicians have stressed that Andes virus — the type of hantavirus that hit the ship and the only kind known to spread person-to-person — requires close and prolonged contact and that it is not a pandemic threat.

The four Canadians who arrived on Vancouver Island Sunday are currently self-isolating on a voluntary basis for at least 21 days and possibly up to six weeks.

Henry said she and the local health officer on Vancouver Island have legal tools to require people to isolate in appropriate facilities. But she said those powers won’t be used, unless the people don’t comply with the request to self-isolate.

“So, it (forced isolation) is a last resort,” she said.

Stephen Hoption Cann, a clinical professor at the University of B.C.’s school of population and public health, said the current voluntary isolation is appropriate given the low chance of transmission.

“It’s not like the COVID-virus,” he said. “It can be transmitted, but not easily transmitted, especially when a patient is not symptomatic.”

If, however, symptoms were to develop, the individuals could be transferred to an isolation unit, he said.

Henry said Sunday that the province has established protocols and facilities in the unlikely event that symptoms develop, including the B.C. Biocontainment Treatment Centre at Surrey Memorial Hospital, to safely assess and care for patients.

“I think we are striking the right balance,” Hoption Cann said, when asked about B.C.’s approach.

“There is a low risk of transmission from this virus. They don’t want to overact. It’s always a delicate balance. If you start (forced) quarantines, you can always have a lot of backlash from that.”

Hoption Cann said the COVID-19 pandemic showed that a lot of people were quite upset with the restrictive measures.

“You just want to maintain overall co-operation from the population, and demonstrate that you are doing the best you can, but not be too extreme under the current situation based on the science of what we know about the virus,” he said.

This report by The Canadian Press was first published May 12, 2026.

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