The rapid surge of mpox in multiple African countries has prompted the World Health Organization to sound its highest level of alert.

On Wednesday, the UN agency declared a global health emergency in response to a severe outbreak of the viral disease in the Democratic Republic of Congo (DRC), which has spread to at least three neighbouring countries where it has not been reported before.

The WHO announcement follows a decision earlier this week by the African Centres for Disease Control and Prevention (CDC) to also declare mpox a public health emergency.

More than 15,600 mpox cases and 537 deaths have been detected in the DRC this year, a situation the WHO Director General Tedros Adhanom Ghebreyesus described as "very worrying".

Children have been most affected by the latest outbreak.

So what does the WHO's global health emergency designation mean? And what are the implications for Australia? Here's what we know so far.

Remind me: What is mpox?

Mpox, formerly known as monkeypox, is an infectious disease caused by the monkeypox virus which was first discovered in 1958. It is endemic in parts of central and west Africa.

Mpox causes a distinctive skin rash or lesions, accompanied by flu-like symptoms, such as fever, sore throat and headache.

It is transmitted through close physical contact with an infected person or animal, and through contaminated materials (such as clothing and linen).

Most people with mpox recover within two to four weeks, but it can cause severe illness, particularly in children, pregnant women, and people who are immunocompromised.

Treatment involves managing the symptoms, and can include pain medicines and antibiotics. There are also antiviral medications undergoing clinical trials that may be administered if more serious complications arise.

Why is this outbreak a concern?

While outbreaks of mpox are not uncommon in the DRC, there has been rapid rise in cases — in the past six months there have been the same number of cases as reported to the WHO for all of last year.

There are two main strains or "clades" of the virus — clade I (once known as the Congo Basin clade), which historically has a higher death rate, and clade II (formerly the West African clade), explains epidemiologist Raina MacIntyre.

The current outbreak is being driven by a new offshoot of clade 1, known as clade 1b, which appears to spread more easily through close contact, including sexual contact. It's the first time the clade 1 mpox virus has been confirmed to spread this way.

"The way [mpox] has spread historically has been in families — one person gets it, other people in the family get sick," says Professor Macintyre, a professor of biosecurity at the Kirby Institute.

"The degree of spread [in this outbreak] is far more than small intra-familial clusters. There's much more widespread transmission."

Outside the DRC, clade 1b has been detected in Kenya, Rwanda and Uganda, while other forms of the mpox virus continue to circulate in central and eastern Africa, and other parts of the continent.

According to the WHO, several outbreaks of different clades "with different modes of transmission and different levels of risk" are occurring, with cases now confirmed in 13 countries.

Data from the African CDC shows children have been most affected: almost 70 per cent of cases and 85 per cent of deaths this year have occurred in those under 15.

Hasn't this happened before?

That's right — the WHO declared a public health emergency of international concern (PHEIC) in July 2022 in response to a significant and unusual outbreak of mpox in non-endemic regions, including Europe, North America, and Australia.

A PHEIC is declared when a disease outbreak is considered serious and unusual, has the potential to spread across borders, and is likely to require international action to contain it.

The 2022 outbreak predominantly affected gay, bisexual and other men who have sex with men, but it was fuelled by a different, less deadly version of the mpox virus known as clade 2b.

"We saw very different epidemiology in 2022, which was mainly sexual transmission, a very low death rate, and in countries that have access to vaccines," Professor MacIntyre says.

After 10 months, the PHEIC was declared over, but the spread of clade 2b has continued, including in Australia, where there's been a resurgence of cases in recent months.

Rhonda Stuart, director of public health and infection prevention at Monash Health, says unlike in 2022, most new cases in Australia are being driven by local transmission, rather than coming from overseas.

"Every case is followed up and we look for upstream and downstream contacts," she says. "But there are some cases we don't know about, so that's how this can be a grumbling issue."

What does it mean for Australia?

So far, no cases linked to the latest outbreak have been detected outside central and eastern Africa.