Sweden reports 1st case of deadlier mpox outside Africa

Sweden has just announced the country's first case of clade 1 mpox, a deadlier version of mpox that previously had been reported only in Africa.

Mpox, formerly known as monkeypox, is caused by a group of viruses with two main branches in their family tree: clade 1 and clade 2. The latter caused the global mpox emergency in 2022 and 2023, which affected countries all over the world, including the U.S., the U.K. and Sweden. In comparison, clade 1 mpox viruses cause more severe disease and death and had never been seen outside Africa — until now.

On Thursday (Aug. 15), the Public Health Agency of Sweden announced the detection of a clade 1 virus in an individual who sought medical treatment in Stockholm. The person was likely infected "during a stay in the part of Africa where there is a major outbreak of mpox clade I," the agency reported.

Clade 1 viruses are a major contributor to ongoing mpox outbreaks in the Democratic Republic of the Congo (DRC) and other African nations, including Burundi, the Central African Republic and the Republic of Congo. The World Health Organization (WHO) declared these outbreaks a public Health emergency of international concern on Wednesday (Aug. 14), flagging a fairly new clade 1 virus as being of particular concern.

Related: Mpox cases are far outpacing last year's numbers, CDC reports

Scientists first detected this form of the virus, dubbed clade 1b, in the DRC. It has since sparked infections in African countries where mpox had never been reported, such as Burundi, Kenya, Rwanda and Uganda.

The Public Health Agency of Sweden did not clarify which subtype of clade 1 virus was detected in their case. Clade 1b is estimated to have a case-fatality rate between 3% and 6%, while in general, clade 1 viruses have reported rates up to 10%. By comparison, in the 2022-2023 outbreak, clade 2 viruses had fatality rates as as low as 0.2%