STOCKHOLM/CHICAGO >> The World Health Organization on Thursday confirmed that a case of the viral infection mpox in Sweden was linked to an outbreak in Africa, the first sign of its spread outside the continent a day after the WHO declared the disease a global public health emergency.

Swedish health officials said at a press conference that the person was infected while in Africa with the clade Ib type of mpox involved in the recent outbreak. The person is receiving treatment.

“This case in Sweden is a warning call for public health authorities to be vigilant and implement robust surveillance and contact-tracing strategies to detect possible new cases early on,” Dr. Jonas Albarnaz, an expert in pox viruses at The Pirbright Institute, said in a statement.

Dr. Brian Ferguson of the University of Cambridge said the case in a Swedish traveler was concerning but not surprising, given the severity and spread of the outbreak in Africa.

“There will likely be more here and in other parts of the world as there are currently no mechanisms in place to stop imported cases of mpox happening,” he said.

The WHO on Wednesday declared the outbreak in Africa a public health emergency of international concern or PHEIC after cases in the Democratic Republic of Congo spread to nearby countries. A PHEIC is WHO’s highest level of alert.

The global vaccine group Gavi told Reuters it has up to $500 million to spend on getting shots to countries affected by the escalating mpox outbreak in Africa.

Both U.S. and Canadian officials have said they have not identified any cases so far.

“This is the first clade I mpox case to be reported outside of the African continent,” CDC spokesman David Daigle said in a statement, noting that the agency is watching the outbreak closely.

The CDC recently issued a Health Alert Network update and updated Travel Health Notice to inform U.S. clinicians, travelers, and public health partners about the spread of clade I mpox into countries that have historically not reported cases of mpox

Clade Ib, the strain of the virus behind the current outbreak, is a new variant of clade I that is endemic in the Congo. Clade Ib appears to spread more easily through routine close contact, including sexual contact.

Clade I mpox tends to cause a higher number of severe infections and have a higher mortality rate than clade II mpox, according to U.S. health officials.

In 2022, WHO declared a public health emergency over an outbreak of mpox caused by clade II, which led to more than 95,000 cases across 115 non-endemic countries.