How Canadian scientists helped uncover sexually transmitted cases of a deadlier mpox strain

If 2022 was the year mpox infections exploded globally, 2023 was the year much of the world stopped paying attention.

Yet Canadian researchers, in collaboration with scientists working on the ground in hot spots such as Nigeria and the Democratic Republic of the Congo (DRC), are still shining a spotlight on the virus that sparked last year's unprecedented global outbreak — and one that still seems capable of new surprises. 

One joint Canadian-DRC research team, co-led by Jason Kindrachuk from the University of Manitoba, has documented what Kindrachuk calls a "massive red flag": the first known cases of a deadlier strain of mpox spreading through sexual contact.

"This is a real concern for us in regard to the potential for the disease to spread broadly," he said.

The World Health Organization (WHO) announced the finding in its latest mpox report, and CBC News obtained an early copy of a since-published paper in which Kindrachuk — and a team of other Canadian, Congolese and international researchers — further outline a cluster of clade I infections linked to sexual transmission. 

There are two main forms of mpox virus: clade I and clade II. The global outbreak in 2022 involved clade IIb, which typically leads to milder illness. By year's end there had been roughly 87,000 infections and more than 100 deaths after the virus spread widely through sexual networks, with the majority of the cases among men who have sex with men. 

Infections of that form of mpox leads to an array of painful and sometimes debilitating symptoms, including both internal and external lesions, but relatively few deaths.

Clade I, in contrast, was long estimated to have a death rate of up to 10 per cent, though the most recent WHO report on an ongoing outbreak in the DRC suggests a case fatality rate of close to five per cent.

Until now, it was also thought to spread mainly through close contact, including surface-based transmission.

5 individuals tested positive

The paper from Kindrachuk's team was published online on Wednedsay by the U.S. Centers for Disease Control and Prevention's Emerging Infectious Diseases journal. 

It outlines how a Congolese man, identified by WHO as a resident of Belgium, had sexual contact with another person in Europe. After arriving in the DRC, the man then tested positive for clade I mpox, and reported that he had sexual contact with nine additional partners, including six men and three women. 

Five people in total ended up testing positive, and all required outpatient treatment and pain control, the research team reported. 

Followup investigations also looked at other possible transmission chains involving 120 additional contacts — including other sexual contacts and family members — but none of those individuals developed mpox during 21 days of follow up.

"We have a tiny piece of the puzzle suggesting something is different now," Kindrachuk said, noting the new finding raises fresh questions about just how often sexual transmission is already happening within the DRC.

Given the increased disease severity associated with this mpox clade, the researchers stressed sexual transmission could impact broader geographical spread of mpox across both clades of the virus.

WHO said another outbreak in the DRC is also being reported, involving multiple cases of mpox among sex workers. These new instances of sexual transmission raise concerns about the rapid expansion of mpox within the country and beyond, given its "internationally mobile" population, the organization continued in its latest report.

DRC experiencing largest annual outbreak

The DRC has been particularly hard hit by the deadlier form of mpox this year. It has been linked to more than 12,000 suspected cases and nearly 600 deaths since the start of the year — the highest number of annual cases ever reported in the Central African nation, WHO figures show.

Worldwide transmission of the milder clade is still simmering as well. 

Though WHO ended its emergency designation for mpox in May, and case reporting in many regions has been scaled back since then, hundreds of clade IIb cases were still reported across dozens of countries this fall.

More than a year into the global outbreak, burning scientific questions about how mpox operates remain unanswered, while hot spots throughout Africa that have endured outbreaks for years still don't have access to vaccines.

"In Congo this year, there are thousands and thousands of cases of mpox, and not a vaccine dose to be found … it's such a slap in the face to our colleagues [in Africa]," said Kindrachuk.

"We shouldn't just be responsive when these types of infectious diseases move into our regions or across our borders and start to present a much greater threat."

The world only became interested in mpox when cases appeared beyond the African continent, said Toronto-based infectious diseases physician Dr. Isaac Bogoch, who is working on DRC mpox research alongside Kindrachuk. 

"This [is] an infection that has been recurring and increasing in frequency over the last couple of decades as the smallpox vaccine programs started to wind down," he said, noting that endemic regions of Africa still lack both vaccines and treatment options.

In contrast, many higher-income countries made vaccines and therapeutics widely available during last year's outbreak.

Vaccine campaigns launched throughout Canada used a smallpox/mpox vaccine manufactured by Bavarian Nordic, for instance, and health-care providers here have also prescribed the smallpox treatment TPOXX off-label for mpox patients.

Canada-Nigeria team also studying mpox transmission

In Nigeria, where the less-virulent clade II version of mpox has been circulating for years, there is also limited access to vaccines. The country's largest outbreak took place in 2017, with 228 suspected cases and 60 confirmed infections.

There, another partnership between Canadian and local researchers is also exploring the dynamics of mpox infections. Rosemary Audu, director of research and head of the microbiology department at the Nigerian Institute of Medical Research, is co-leading that work.

Audu said researchers are collecting samples from multiple sources — including symptomatic sex workers and household pets living with people who had prior mpox infections — to get a better sense of the virus' transmission patterns and which animals can carry and spread it. It's already known to infect certain mammals, such as squirrels and monkeys, but scientists aren't yet sure just how many other species may be susceptible. 

"We're spreading our tentacles wide," Audu said.

Ongoing research, increased vaccine access, and continued collaboration between international clinicians and virologists are all crucial steps toward understanding and containing this potentially-deadly virus, according to Audu.

"The world is a global village and things can move very easily from one country to another … so I think the best thing to do is just to be vigilent," she said.