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Scientists comment on reports of a case of Clade 1 Mpox in Sweden.
Dr Jonas Albarnaz, a Research Fellow specialising in pox viruses at The Pirbright Institute, said:
“There are diagnostic PCR tests that can differentiate between clade 1 and clade 2 mpox virus based on genetic differences between these two virus strains. So far, sequencing of the virus genome has been used to confirm clade 1b cases in Africa. However, the availability of these new clade 1b genomes will allow the development of diagnostic PCR tests to differentiate between clade 1 and clade 1b as well.
“This news of a case of Clade 1 mpox in Sweden is concerning for two main reasons. First, this is the first clade 1 mpox virus case outside Africa. This indicates that the extent of the international spread of clade 1 outbreak in DRC might be larger than we knew yesterday. And second, clade 1 mpox virus is associated with a more severe disease and higher mortality rates than the clade 2 virus responsible for the international mpox outbreak in 2022.
“This is hard to predict whether we will see further cases of Clade 1 mpox outside of Africa, but 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. It’s also critical to determine what is the link between this clade 1 monkeypox virus detected in Sweden and the ongoing outbreak in DRC.”
Some background on previous mpox cases and outbreaks outside of Africa:
“The 2003 outbreak in the USA was associated with prairie dogs infected with clade 2 that had been imported from Africa. Prior to the 2022 international outbreak of clade 2, a few clade 2 cases were reported outside Africa but they were imported from endemic countries in Africa.”
Dr Brian Ferguson, Associate Professor of Immunology, University of Cambridge, said:
“The appearance of a case mpox disease caused by clade 1 mpox virus in Sweden is clearly a concerning development. It is not surprising, given the severity and spread of the outbreak in Africa, that travel between continents has brought this case to Europe. There will likely be more here and in and other parts of the world as there are currently no mechanisms in place to stop imported cases of mpox happening. The timing of this case comes less than 24 hours after the WHO’s PHEIC declaration and only 15 months after the WHO ended the previous mpox PHEIC in May 2023. The lack of activity in the intervening period has resulted in what could now become a new global outbreak. There should have been a greater effort to produce and distribute vaccines to the affected areas, but this has not happened. It is possible to address these problems but this requires rapid international co-operation.”
Prof Francois Balloux, Professor of Computational Systems Biology and Director, UCL Genetics Institute, UCL, said:
“The recent case of mpox detected in Sweden was likely diagnosed as clade I through whole genome sequencing. Whether the case belonged to the I or Ib lineage has not been released so far. The person who has been diagnosed in Sweden has been infected during a stay in a part of Africa where mpox is endemic. As such, there is no evidence for transmission in Europe at this stage. Given the sizeable number of recent mpox clade I cases in parts of Africa, it is not surprising that a case has been diagnosed in a European country. At this stage, Sweden is not taking additional measures beyond those already in place. It is to be expected that other imported cases of mpox clade I will be identified outside Africa over the coming months.”
Declared interests
Dr Jonas Albarnaz: I was part of the UKRI Mpox Research Consortium (led by Geoff Smith and Bryan Charleston), but this funding has ended.
Dr Brian Ferguson: No conflict of interests to declare.