Mpox is a global emergency again. How deadly is it? What are 'clades'? What you need to know
Evolving virus remains a threat as scientists aim to understand transmission patterns and death rate
Mpox first made global headlines in 2022 when the virus suddenly exploded around the world, spreading rapidly through sexual networks into dozens of new countries outside Africa.
The World Health Organization labelled it a public health emergency of international concern that same year. The global outbreaks overwhelmingly impacted men who have sex with men, leading to a range of symptoms from mild illness, to painful, debilitating lesions to, in some cases, hospitalization or death.
After global cases cooled down, the WHO ended its emergency declaration. But the virus didn't go away.
Instead, in the last two years, new challenges started bubbling in the Democratic Republic of Congo (Congo, also known as Congo-Kinshasa), a country in the heart of Africa that's been dealing with mpox for decades.
Case counts of a serious form of the virus in Congo soared to new heights, hitting more than 15,000 known infections so far this year, along with hundreds of deaths. It's an alarming spike partly fuelled by the spread of an evolving new lineage, which is now showing up in several neighbouring countries for the first time.
The growing crisis prompted back-to-back announcements this week, with the Africa Centers for Disease Control and Prevention (Africa CDC) and WHO declaring a continental then global health emergency.
Just a day after the WHO's warning, Swedish health officials announced a patient who'd recently traveled to Africa was recently diagnosed with Congo's form of mpox — the first known case ever recorded outside the African continent, and a potential harbinger of more global infections to come.
So what exactly is mpox, how is this dangerous virus changing and spreading, and why is the situation in 2024 different from earlier outbreaks?
What is mpox?
This pox virus, formerly known as monkeypox, was first identified in a human back in 1970 and was largely confined to parts of Africa in the decades that followed.
Mpox often causes mild disease, and is known for its namesake pox lesions. They can be filled with pus, often cause excruciating pain, and leave lifelong scars — both externally or internally — including within the genital region.
The viral infection also causes a fever, sore throat, headache, muscle aches, back pain, and swollen lymph nodes.
It spreads in various ways, including through close contact in household settings and through sexual contact, though scientists are still trying to unravel its exact transmission patterns.
What are the different types of mpox?
There are two main forms of mpox virus: clade I and clade II.
'Clade' is a virology term, similar to the variants used to describe offshoots of SARS-CoV-2, the virus behind COVID-19. In both cases, it's a way for scientists to track each virus's evolutionary family tree.
The global mpox outbreak in 2022 was dominated by clade II, which typically leads to milder illness and spread around the world through sexual contact.
Clade I, in contrast, has long circulated within Congo. It's been linked to more serious disease and higher death rates, but historically spread mainly from infected animals to people in the country's rural regions, often striking vulnerable children.
More recently, those clade I transmission patterns started to shift.
Back in 2023, a Canadian-Congolese research team published findings showing the mpox virus circulating in Congo was also spreading through sexual networks.
By April this year, the same researchers identified a new lineage — known as clade Ib — which showed signs of efficient human-to-human transmission and was striking high numbers of sex workers. At the time, the team warned it could soon spread beyond Congo.
That's the type of mpox now hopping across borders into new countries like Burundi, Kenya, and Uganda, prompting renewed global concern.
"What is happening in Congo right now is we have the majority of cases still related to [an earlier strain] — still related to zoonotic transmission, still having the greatest mortality and morbidity among children — but we have this rise now of sexual contact-based transmission with clade Ib," explained research team member Jason Kindrachuk, a microbiologist with the University of Manitoba.
How deadly is this new form of mpox?
The Africa CDC estimates suggest roughly three to four per cent of mpox sufferers in Congo end up dying from their illness.
That's much higher than the less than one per cent death rate reported in the clade II global outbreak, but a far cry from the 30 per cent death toll from the virus's infamous cousin, smallpox, the only disease eradicated around the world thanks to widespread vaccination efforts.
Children, people who are pregnant, and individuals with weakened immune systems — including people with HIV — are all at the highest risk of severe illness from mpox.
But without an accurate tally of the total number of infections in Congo, it's tricky to know clade Ib's exact death rate, or how it compares to other offshoots of the virus.
That's partly because of major differences in the population demographics and the level of healthcare resources in various regions. Close to half of Congo's total population is under the age of 15, for example, and the country continues to experience high rates of HIV, both of which could impact disease severity in ways that have nothing to do with the virus itself.
Kindrachuk said testing limitations, such as the inability to transport samples through much of Congo, and the fact that many mild cases fly under the radar, also hamper scientists' efforts to understand the full picture.
"Ninety per cent of cases are never actually tested, so we are actually only diagnostically confirming about 10 percent," he added.
Dr. Maria Van Kerkhove, who leads the WHO's department of epidemic and pandemic preparedness and prevention, called for more surveillance during the organization's Wednesday briefing.
"We need standardized data collection on the patients that are infected with mpox to understand the disease course, the severity of this," she said.
Why are scientists so worried?
For months, researchers have raised alarms that clade Ib could eventually explode worldwide, causing a repeat of the 2022 outbreak — but with unknown, and potentially devastating, global consequences.
The case recently identified in Sweden, a patient who sought care in the Stockholm region, offered yet another early warning.
Congolese-American infectious disease epidemiologist Jean Nachega, with the University of Pittsburgh, called mpox a "ticking time bomb" that's proven capable of spilling into new countries over and over, from a part of the world with few resources to contain it.
While higher-income countries, Canada included, stamped out high case counts of clade II through vaccination programs, Africa hasn't had the same resources. The Africa CDC is aiming to roll out 10 million mpox vaccine doses, officials said Tuesday, but has only procured a small portion of that total.
There's also a lack of therapeutics across the continent, and a drug used elsewhere to successfully treat mpox patients, an antiviral called tecovirimat, or TPOXX, doesn't appear to work against clade I.
New findings, published Thursday by the U.S. National Institute of Allergy and Infectious Diseases (NIAID), showed TPOXX did not reduce the duration of mpox lesions among children and adults with clade I mpox in Congo, based on an initial analysis of data from a randomized, placebo-controlled trial.
In a statement, NIAID Director Dr. Jeanne Marrazzo called the early results "disappointing."
But the team did suggest there's a silver lining: the 1.7 per cent overall death rate among study participants, regardless of whether they received the drug or not, was lower than the mpox mortality seen among all known cases in Congo.
"This shows that better outcomes among people with mpox can be achieved when they are hospitalized and provided high-quality supportive care," the team wrote.
While Nachega said the mpox crisis is "worrisome," he expressed hope that this week's WHO declaration of a global emergency could help turn the situation around and encourage the international community to provide Africa with more support.
"This has been an endemic disease, and a neglected disease, but hopefully now the proper attention is going to be put on it so we can get better diagnostics, better treatment and better prevention," he said.
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With a file from Melanie Glanz
