What is hantavirus? Everything you need to know

Hantavirus, a rodent-borne malady, is suspected of causing a deadly outbreak aboard a luxury cruise ship.

Around 150 people including four Canadians, were still stuck on the vessel that was being held off West Africa after three people — a Dutch couple and a German national — died and others fell ill, including a Briton who left the Dutch-flagged MV Hondius and was being treated in South Africa, according to authorities.

The World Health Organization (WHO) said in a statement Sunday that detailed investigations of the cruise ship outbreak are ongoing, including further laboratory testing and epidemiological investigations.

The virus is also being sequenced, which involves looking at its genetic makeup to identify what strain of the virus it is. Once they determine that, they may be able to better predict symptoms and understand the way the virus spread.

The disease gained attention last year after musician Betsy Arakawa, the wife of late actor Gene Hackman, died from a hantavirus infection in New Mexico.

The virus is spread by rodents and more rarely, people.

Multiple hantaviruses have been reported around the world, and all are spread by rodents such as rats and mice. Five species in North America are known to carry hantaviruses, three of which are commonly found in Canada: the deer mouse, white-footed mouse and red-backed vole. 

Studies indicate hantaviruses have been around for centuries, with outbreaks documented in Asia and Europe. In the Eastern Hemisphere, it has been linked with hemorrhagic fever and kidney failure.

It wasn't until the early 1990s that a previously unknown group of hantaviruses emerged in the southwestern United States as the cause of an acute respiratory disease now known as hantavirus pulmonary syndrome.

Suspected hantavirus outbreak on cruise ship kills 3, sickens 3 others: WHO

Hantavirus is mainly spread by contact with rodents or their urine, saliva or droppings, particularly when the material is disturbed and becomes airborne, posing a risk of inhalation.

People are typically exposed to hantavirus around their homes, cabins or sheds, especially when cleaning out enclosed spaces with little ventilation or exploring areas where there are mouse droppings.

The rodents that carry hantavirus don't show signs of sickness themselves.

WHO says that while it rarely happens, hantaviruses can also spread directly between people.

Human-to-human transmission has been found with a type of hantavirus found in the Americas called the Andes virus, according to WHO.

The organization said when transmission has happened, it's been due to close and prolonged contact, specifically between people who live together or are intimate partners, and is most likely to happen during the early stages of the illness, "when the virus is more transmissible."

The symptoms of a hantavirus infection can appear anywhere from one to eight weeks after exposure, but on average they appear after two weeks.

The range of symptoms includes severe fatigue, fever, muscle pain, headache and nausea, and can progress to difficulty breathing. 

"Early in the illness, you really may not be able to tell the difference between hantavirus and having the flu," said Dr. Sonja Bartolome of the University of Texas Southwestern Medical Center in Dallas.

The other syndrome caused by hantavirus — hemorrhagic fever with renal syndrome — usually develops within a week or two of exposure.

There are no antiviral medications available to treat a hantavirus infection, but early medical attention can increase the chance of survival.

The typical course of treatment involves admission to intensive care, where a medical team will try to ease the patient's symptoms, including by providing oxygen and putting them on a ventilator.

Reported fatality rates from hantavirus pulmonary infection ranges anywhere from 20 to 50 per cent, depending on the strain of the virus. 

The fatality rate in British Columbia is about 44 per cent, according to a 2023 report by the B.C. Centre for Disease Control.

In 2015, the U.S. Centers for Disease Control and Prevention pegged the overall fatality rate at 36 per cent. Given the high fatality rate, researchers have described it as "one of the most severe infectious diseases endemic to the United States." 

The death rate for hemorrhagic fever with renal syndrome varies from one per cent to 15 per cent of patients, according to the CDC.

Since surveillance began in the early 1990s, 163 cases of hantavirus pulmonary syndrome have been confirmed by the National Microbiology Lab in Winnipeg, part of the Public Health Agency of Canada, according to an interview with the lab last year.

That works out to an average of roughly five cases in Canada each year. 

"It is a fairly hard disease to acquire from the environment, not impossible, but certainly given the amount of rodents in our environment it's pretty rare," said Dr. Zain Chagla, an infectious disease specialist in Hamilton.

A 2020 report led by National Microbiology Lab scientists showed a geographic breakdown of confirmed cases, with more than half found in Alberta (73), followed by smaller numbers in Saskatchewan (28), British Columbia (16) and Manitoba (5).

In Canada, only one case of transmission to humans was reported east of the Prairie provinces, in Quebec. Researchers believe this is because of genetic differences between the hantaviruses carried by rodents in eastern and western parts of North America.  

Of the 143 confirmed Canadian cases in that 2020 report, 34 were fatal.  

Most hantavirus infections in Canada happen in the spring and early summer, often because that's when people are entering enclosed spaces where deer mice have been active, combined with seasonal increases in deer mouse populations. 

Health experts advise people who are opening a cabin, cottage or trailer that's been closed for the winter to air out the structure as much as possible and wear a mask and gloves when cleaning any mouse waste to prevent transmission of the virus. 

A bleach solution should also be used when cleaning rodent droppings. Public health experts caution against sweeping or vacuuming, which can cause virus particles to get into the air.

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