Mpox is a global emergency again. How deadly is it? What are 'clades'? What you need to know

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?

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.

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.