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 has obtained the forthcoming 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.

The paper from Kindrachuk's team 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 contacts 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.