Sweden’s public health agency has recorded what it says is the first case of a more dangerous type of mpox outside the African continent.

The person became infected during a stay in an area of Africa where there is currently a major outbreak of mpox Clade 1, the agency said.

The news comes just hours after the World Health Organization (WHO) declared that the outbreak of mpox in parts of Africa was now a public health emergency of international concern.

At least 450 people died during an initial outbreak in the Democratic Republic of Congo and the disease has since spread to areas of Central and East Africa.

According to Olivia Wigzell, the acting head of the Swedish public health agency, the infected person had sought care in the Stockholm area and the fact that they were receiving treatment in Sweden did not mean there was a risk to the broader population.

“The affected person has also been infected during a stay in an area of Africa where there is a large outbreak of mpox Clade 1,” she told a news conference.

Mpox, which was previously known as monkeypox, is transmitted through close contact, such as sex, skin-to-skin contact and talking or breathing close to another person.

It causes flu-like symptoms, skin lesions and can be fatal, with four in 100 cases leading to death. It is most common in the tropical rainforests of West and Central Africa and there are thousands of infections every year.

There are currently a number of outbreaks of mpox that are taking place simultaneously and they are partly fuelled by the newer and more serious type of Clade 1b, identified in September last year.

There are two types of Clade 1 and the Swedish case has been identified as Clade 1b. Since mpox Clade 1b was first witnessed in Democratic Republic of Congo there have been confirmed cases in Burundi, Kenya and Rwanda, before the new case identified in Sweden.

While Clade 2 did cause a public health emergency in 2022, it was relatively mild and some 300 cases have already been identified in Sweden.

WHO/Europe said it was actively engaging with Sweden’s health authorities on “how best to manage the first confirmed case of mpox Clade 1b”.

It urged other countries to act quickly and transparently like Sweden, as there were likely to be further “imported cases of Clade 1 in the European region over the coming days and weeks”.

The Swedish public health agency said the more dangerous outbreak was likely to be linked to “a higher rise of a more severe course of disease and higher mortality”.

Dr Jonas Albarnaz, who specialises in pox viruses at the Pirbright Institute, said the first case outside of Africa was concerning as it meant the spread “might be larger than we knew yesterday”.

Dr Brian Ferguson, Associate Professor of Immunology at the University of Cambridge agreed it was “clearly a concerning development” but unsurprising given the severity and spread of the outbreak in Africa.

The WHO hopes its latest declaration, that mpox is a public health emergency of international concern, will trigger greater support to the areas most affected.

Vaccines are available, for those at greatest risk or who have been in close contact with an infected person, but many experts worry there are not enough jabs or funding to get them to the people who need them most.

The mortality rate from the Clade 1b variant in Sweden will not be as high as that seen in parts of Africa, because of the high quality of healthcare in Europe.

However, Dr Ferguson said there would likely be further cases in Europe and other parts of the world “as there are currently no mechanisms in place to stop imported cases of mpox happening”.

The European Centre for Disease Prevention and Control said symptoms usually appeared 6-13 days after infection, through fevers and headaches, rashes or sores and muscle ache.

Most people experienced mild to moderate symptoms followed by a full recovery, but immuno-compromised individuals were at greater risk.

While news of the first case outside Africa may cause alarm, it was to be expected.

As other disease outbreaks have shown, swift international action can help stop the disease spreading further.