As global outbreaks of monkeypox made headlines, Dr. Antoine Cloutier-Blais's Montreal clinic began seeing patients with unusual — and often painful — bodily lesions.

By early June, the family physician and his colleagues had treated around 15 patients with confirmed infections, out of the roughly 100 lab-confirmed cases reported so far in Quebec. People with suspected infections soon started showing up to the clinic on a near-daily basis.

Cloutier-Blais began to notice some interesting trends.

The pox lesions, he found, weren't presenting exactly like what he'd seen in photos circulating online of people infected in parts of Africa, where the virus had been found for decades. 

"Lesions are much smaller and usually very much localized," he said, adding there's also a "very wide spectrum of different kinds of presentations."

In some cases, lesions are showing up on or inside various bodily areas, including patients' mouths, genitals or anal region, sometimes spreading to the limbs or torso or popping up across the entire body.

But for other patients, visible symptoms have been far more subtle — even just a single mark on the skin.

Medical experts in multiple countries are noticing similar patterns. In this unprecedented outbreak — which is offering many global clinicians their first real-world experience with this disease — there's a clear range in severity, from classic full-body rashes requiring hospital stays and pain medication, all the way to instances where monkeypox presents as a mild infection that may be easy to miss or easy to confuse with other conditions.

And while these infections are typically treatable, there's also growing concern this virus could spread into vulnerable populations at a higher risk of life-threatening disease.

Monkeypox often shows up as a flu-like illness, featuring symptoms like fever, chills, and muscle stiffness that can predate the telltale lesions.

Yet, for recent patients in the U.S., the emergence of a rash was often the first warning sign that they were sick. 

"In these new cases, what we're hearing is that those [pre-rash] symptoms might be really mild or not even noticed at all," said Dr. Agam Rao, medical officer of the U.S. Centers for Disease Control and Prevention's Poxvirus and Rabies Branch, during an interview with the medical journal JAMA.

For clinicians unfamiliar with the virus, it may also be hard to differentiate some monkeypox infections from chickenpox — or certain sexually transmitted infections like herpes and syphilis.

"Monkeypox can masquerade as other conditions," said Dr. Rosamund Lewis, a Canadian physician and the technical lead at the World Health Organization (WHO) for the monkeypox outbreak.

WATCH | Quebec officials work to contain monkeypox outbreak:

Bodily lesions tied to this virus are also typically thought to start around the head, before progressing down toward the arms and legs, yet Rao said U.S. patients have been experiencing rashes in the genital or perianal regions first, including some people who've suffered from inflammation of the rectum. 

One case study published in the infectious disease medical journal Eurosurveillance looked at the experience of one HIV-positive man in his 30s who was diagnosed with monkeypox in May after travelling and engaging in sexual activity in Europe. 

The man's initial symptoms were painless pustules on the penis, which soon worsened. The lesions became painful and itchy, then the man developed a fever three days later, with the rash spreading to his torso, face and limbs in the days that followed — requiring two trips to his physician and one brief hospital stay.

"When examined in hospital, the penile lesions had largely formed scabs and the lesions on hands and lower limbs were painless papular pustules," the authors of the case study wrote.

Monkeypox isn't known to be a sexually transmitted infection, but it can spread through various forms of close contact with others. That includes skin-to-skin contact, even if someone just has minimal lesions in their genital regions, or through respiratory droplets if someone has a lesion inside their mouth, the WHO's Lewis noted.

While there are some reports of women recently becoming infected around the world, the bulk of infections in this global outbreak — now at roughly 1,000 confirmed cases and counting — have been among men who have sex with men, prompting awareness campaigns by and for members of that community. 

"Of course, monkeypox can affect anyone, any gender, any sexual orientation," said Dane Griffiths, director of the Gay Men's Sexual Health Alliance in Ontario, where roughly a dozen cases have been reported, largely in Toronto.

"But given the current cases that we're seeing, and the questions that are outstanding around the dynamics of monkeypox transmission in our community, we are making folks aware of it."

WATCH | WHO urges countries to halt monkeypox transmission:

Cloutier-Blais stressed the importance of the community's rapid mobilization, including "impressive" participation in monkeypox vaccination clinics in Montreal. 

Since the launch in late May, more than 1,600 doses have been provided to members of the public who may be at a higher risk of contracting monkeypox through sexual contact or work-related reasons. 

"Anybody could eventually experience symptoms," Cloutier-Blais said.

When it comes to mild cases, the Montreal physician said his patients haven't required much medical support.

"We simply suggest to individuals to cover their lesions and stay isolated as much as possible, with a mask on if they need to meet other people, and otherwise remain at home and cover their lesions until they're fully healed," he explained.

More serious cases, however, have required hospitalization, with patients experiencing "very severe fever or pain that is difficult to manage just through oral medication."

So far, no one has died during this recent global outbreak outside of Africa, the WHO's director-general Tedros Ghebreyesus told a press conference on Wednesday. But the disease can be deadly in some cases, particularly for higher-risk groups such as pregnant individuals, children, and people with compromised immune systems.

Tedros called on countries to make serious efforts to stop further virus transmission in order to prevent monkeypox from taking hold more broadly and spreading into those vulnerable populations.

"The risk of monkeypox becoming established in non-endemic countries is real," he said.

Senior Health & Medical Reporter

Lauren Pelley covers health and medical science for CBC News, including the COVID-19 pandemic, Canadian health policy, and the global spread of infectious diseases. She's based in Toronto. Contact her at: lauren.pelley@cbc.ca

Add some “good” to your morning and evening.

A variety of newsletters you'll love, delivered straight to you.

Audience Relations, CBC P.O. Box 500 Station A Toronto, ON Canada, M5W 1E6

Toll-free (Canada only): 1-866-306-4636

TTY/Teletype writer: 1-866-220-6045

It is a priority for CBC to create a website that is accessible to all Canadians including people with visual, hearing, motor and cognitive challenges.

Closed Captioning and Described Video is available for many CBC shows offered on CBC Gem.