If new mpox strain hits Montreal, ‘we don’t know how it’s going to behave’

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The new strain of monkeypox causing a serious outbreak in several African countries will probably reach Montreal and when it does, the public health response required may be different than during the city’s 2022 outbreak, scientists say.

So far no cases of clade Ib, the strain of the virus driving an ongoing outbreak that began in the eastern Democratic Republic of Congo, have been found in North America, but that strain has now spread from the D.R.C. to neighbouring countries and cases have been detected in Sweden and Thailand.

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Dr. David Kelvin, a microbiology and immunology professor at Dalhousie University in Halifax, said he expects that the disease will eventually arrive in Canada.

“It seems impossible that it wouldn’t,” said Kelvin, whose team was the first to sequence the genome of the clade Ib strain and the first to research its chain of transmission.

Kelvin said he was working on environmental issues affecting mpox in the area around Lake Kivu, an African Great Lake along the border between the D.R.C. and Rwanda, last fall when he heard about mpox cases in the South Kivu province, where the disease had been very rare.

“We started to see an enormous amount of human-to-human transmission of mpox,” he said.

Clade I viruses are normally encountered in animals, often wild animals eaten for food, he said, and while they can be transmitted from one person to another, those transmission chains are usually short. However, in this case, “there’s excellent evidence for sustained long-term transmission” among people, he said.

Initially, the disease, which often spreads by contact with lesions on an infected person, began spreading among sex workers, but it has since begun spreading through other forms of sustained contact, Kelvin said, including among children, which he believes is because they’re playing together in close quarters. It has also spread from women to their hairdressers.

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Those lesions sometimes cover the body and are often found around the genitals.

“These lesions are a bridge source of high viral load, so coming in contact with these lesions is extremely hazardous and opens people up to infection,” Kelvin said.

In the Kivu region, there are now 4,000 suspected cases — that’s a likely undercount and a dramatic increase from a few months before — and Kelvin said there’s a lack of studies about the possibility of droplet or even airborne transmission.

“With so many cases, there will be pressure for the virus to mutate, just like we found with COVID, where we saw Omicron become much more transmissible than the earlier versions of Omicron,” he said. “So my big worry is that additional mutations will make it an airborne virus that is highly transmissible.”

The 2022 outbreak in Montreal, as in other parts of North America and Europe, largely affected men who have sex with men, but because high-risk communities were targeted by vaccination campaigns in 2022, members of that group as well as health-care workers will probably be protected from the new strain, said Dr. Donald Vinh, an infectious disease specialist at the McGill University Health Centre.

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Vinh said he’s “moderately worried” about what the arrival of the disease would mean in Montreal. A key worry is that a lack of testing in regions where the virus is spreading has made scientific research about the way it’s being transmitted difficult, he said.

When the virus arrives here, it will probably spread through different communities than in the D.R.C.

“The issue is that the virus transmits through the path of least resistance, but the path of least resistance can vary based on your societal construct and so that’s the issue that we have to face: We don’t know what’s going on there, but we also don’t know how it’s going to behave once it’s here,” he said in a recent interview. 

Research has suggested clade Ib causes more serious illness than clade II.

A National Institutes of Health study has shown that a mortality rate of between four per cent and five per cent, but that would probably be much lower in Canada, Vinh said. “The distinguishing feature of whether you did well or you didn’t from mpox was whether you had access to health care.”

Vinh said there’s no sign the existing vaccine will be less effective against clade Ib but, as with access to treatment, global inequality means vaccines aren’t available in regions where the virus is spreading.

In Montreal, he said, education is important to ensure the disease is recognized quickly by medical professionals.

“When it’s going to appear, because it’s going to appear, when it’s going to appear, we don’t know where or when, but it’s going to necessarily lead to someone seeking medical attention,” he said.

Montreal public health said five cases of mpox — all clade II — have been detected in the city so far this year, fewer than the year before and that information has been sent out to help health-care professionals look for the disease.

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