What is mpox and why has the WHO declared it a public health emergency?

The World Health Organization has declared mpox a global public health emergency for the second time in two years, following the spread of an outbreak in the Democratic Republic of Congo to neighboring countries.

New cases of the virus have since been been identified outside of the continent, in countries including Thailand, Philippines, Swedenand Pakistan.

Health officials are raising concerns because many of the new cases in Africa have been identified as a new and deadlier strain, known as clade 1b. The new strain has also been confirmed outside of the continent, in Thailand.

CNBC breaks down what we know so far.

Mpox is a viral infectionthat spreads through close contact, including sexual contact. It causes flu-like symptoms, including fever, chills and muscle aches, as well as lesions filled with pus. While usually mild, it can be fatal.

There are broadly two types of of mpox, known as clades, with the latest outbreak identified as clade 1. The current strain appears to spread more easily and has a higher fatality rate when compared with the 2022 strain known as clade 2.

It also appears to disproportionately affect young people, with most deaths occurring among children.

A new offshoot of clade 1, known as clade 1b, is said to be responsible for the recent uptick in cases, according to the WHO.

The WHO said that clade 1b is spreading person to person, often through sexual contact. While first identified in 2024, it is thought to have emerged in the DRC around 2023.

"The outbreak associated with clade Ib in the DRC primarily affects adults and is spreading rapidly, sustained largely, but not exclusively, through transmission linked to sexual contact and amplified in networks associated with commercial sex and sex workers,"