Swedish health authorities on Thursday said they had registered the first case outside Africa of the more dangerous variant of mpox, a viral infection that spreads through close contact.

The announcement came a day after the World Health Organization (WHO) declared mpox a global health emergency for the second time in two years, warning the virus might ultimately spill across international borders.

Sweden's Public Health Agency confirmed to Agence France-Presse (AFP) that the case was the same strain of the virus that has surged in the Democratic Republic of Congo since September 2023, known as the Clade 1b subclade.

The person was infected while staying in a part of Africa where there was a large outbreak of the disease, Olivia Wigzell, director-general at the Swedish Public Health Agency told a press conference.

"A person who sought care" in Stockholm "has been diagnosed with mpox caused by the Clade I variant. It is the first case caused by Clade I to be diagnosed outside the African continent," the agency said in a statement.

Wigzell said the infected person had received care and instructions in accordance with the health agency's recommendations.

"The case is the first caused by Clade I that has been diagnosed outside the African continent. The affected person has also been infected during a stay in an area of Africa where there is a large outbreak of mpox Clade I," she said.

The agency added that Sweden "has a preparedness to diagnose, isolate and treat people with mpox safely."

"The fact that a patient with mpox is treated in the country does not affect the risk to the general population, a risk that the European Centre for Disease Prevention and Control (ECDC) currently considers very low," it said.

The Africa Centers for Disease Control and Prevention declared mpox a public health emergency on the continent on Tuesday.

WHO said there have been more than 14,000 cases and 524 deaths in Africa this year, which already exceed last year's figures.

So far, more than 96% of all cases and deaths are in a single country – Democratic Republic of Congo. Scientists are concerned by the spread of a new version of the disease there that might be more easily transmitted among people.

Here's a look at what we know about mpox, and what might be done to contain it:

Mpox, also known as monkeypox, was first identified by scientists in 1958 when there were outbreaks of a "pox-like" disease in monkeys. Until recently, most human cases were seen in people in central and West Africa who had close contact with infected animals.

In 2022, the virus was confirmed to spread via sexual intercourse for the first time and triggered outbreaks in more than 70 countries across the world that had not previously reported mpox.

Mpox belongs to the same family of viruses as smallpox but causes milder symptoms like fever, chills and body aches. People with more serious cases can develop lesions on the face, hands, chest and genitals.

The number of cases has jumped dramatically. Last week, the Africa CDC reported that mpox has now been detected in at least 13 African countries. Compared with the same period last year, the agency said cases are up 160% and deaths have increased by 19%.

Earlier this year, scientists reported the emergence of a new form of mpox in a Congolese mining town that can kill up to 10% of people and may spread more easily.

Unlike in previous mpox outbreaks, where lesions were mostly seen on the chest, hands and feet, the new form of mpox causes milder symptoms and lesions on the genitals.

That makes it harder to spot, meaning people might also sicken others without knowing they're infected, said Dr. Placide Mbala-Kingebeni, a Congolese researcher who led the research into the new form of mpox.

WHO said mpox was recently identified for the first time in four East African countries: Burundi, Kenya, Rwanda and Uganda. All of those outbreaks were linked to the epidemic in Congo.

WHO director-general Tedros Adhanom Ghebreyesus said there was concern for the further spread of the disease within Africa and beyond.

In the Ivory Coast and South Africa, health authorities have reported outbreaks of a different and less dangerous version of mpox that spread worldwide in 2022.

Kamituga, the region in Congo where the new form of mpox was first spotted, is home to a significant transient population traveling through Africa and beyond.

Still, given the resources in rich countries to stop mpox, scientists suspect that if new outbreaks linked to Congo were to be identified, transmission could be stopped relatively quickly.

Unlike COVID-19 or measles, mpox is not airborne and typically requires close, skin-to-skin contact to spread.

WHO's emergency declaration is meant to spur donor agencies and countries into action. However, the global response to previous declarations has been mixed.

Africa CDC Director General Dr. Jean Kaseya said the agency's declaration of a public health emergency was meant "to mobilize our institutions, our collective will and our resources to act swiftly and decisively." He appealed to Africa's international partners for help, saying that the escalating caseload in Africa had largely been ignored.

Dr. Boghuma Titanji, an infectious diseases expert at Emory University, said the last WHO emergency declaration for mpox "did very little to move the needle" on getting things like diagnostic tests, medicines and vaccines to Africa.

During the global outbreak of mpox in 2022, gay and bisexual men made up the vast majority of cases and the virus was mostly spread through close contact.

Although some similar patterns have been seen in Africa, children under 15 now account for more than 70% of the mpox cases and 85% of deaths in Congo.

Greg Ramm, Save the Children's Congo director, said the organization was particularly worried about the spread of mpox in the crowded camps for refugees in the east, noting there were 345,000 children "crammed into tents in unsanitary conditions." He said the country's health system was already "collapsing" under the strain of malnutrition, measles and cholera.

Emory's Titanji said it was unclear why children were so disproportionately hit by mpox in Congo. She said it might be because kids are more susceptible to the virus or that social factors, like overcrowding and exposure to parents who caught the disease, might explain it.

The 2022 outbreak of mpox in dozens of countries was largely shut down with the use of vaccines and treatments in rich countries, in addition to convincing people to avoid risky behavior. But barely any vaccines or treatments have been available in Africa.

Marks, of the London School of Hygiene and Tropical Medicine, said that immunization would likely help – including inoculating people against smallpox.

"We need a large supply of vaccine so that we can vaccinate populations most at risk," he said.

Congolese authorities have asked for 4 million doses mostly for young children, but no doses have yet been received, said Cris Kacita Osako, coordinator of Congo's Monkeypox Response Committee.