HANDOUT - 18.05.2022, USA, ---: Diese elektronenmikroskopische Aufnahme aus dem Jahr 2003, die von den Centers for Disease Control and Prevention zur Verfügung gestellt wurde, zeigt reife, ovale Affenpockenviren (l) und kugelförmige unreife Virionen (r), die aus einer menschlichen Hautprobe im Zusammenhang mit dem Präriehundeausbruch von 2003 stammt. Die Zahl der beim Robert Koch-Institut (RKI) erfassten Affenpocken-Nachweise in Deutschland ist auf mehr als 200 gestiegen. (zu dpa «RKI: Nun knapp 230 Fälle von Affenpocken in elf Bundesländern») Foto: Cynthia S. Goldsmith/Russell Regner/CDC/AP/dpa - ACHTUNG: Nur zur redaktionellen Verwendung und nur mit vollständiger Nennung des vorstehenden Credits +++ dpa-Bildfunk +++

The causative agent of the current outbreak of monkeypox has mutated surprisingly, according to a study. Compared to related viruses from 2018 and 2019, there are around 50 differences in the genome, writes a team from Portugal in the journal “Nature Medicine”.

This is far more than would have been expected based on previous estimates for this type of pathogen: roughly six to twelve times more. The divergent branch could be a sign of accelerated evolution. The work is mainly based on analyzes of Portuguese cases.

So far, experts had spoken of a generally rather slow development with regard to this type of virus – especially compared to the very numerous mutations of Sars-CoV-2.

The authors of the study suspect that the current outbreak is due to one or more imports from a country in which the virus is permanently present. Superspreader events and international travel then seemed to have promoted further spread. “Our data provide additional evidence of ongoing viral evolution and possible adaptation to humans,” writes the team led by João Paulo Gomes from the National Institute of Health Doutor Ricardo Jorge (INSA) in Lisbon.

The expert on the evolution of viruses, Richard Neher (Basel), explained that the mutation rate was “indeed surprisingly high”. The mutations would have a very specific pattern. The authors suspected that enzymes of the human immune system are responsible for these changes in the genome.

“Even within the current outbreak, we are seeing this accelerated mutation. The rate is roughly one mutation per genome per month – with some uncertainty,” said Neher. Sars-CoV-2 has about two mutations per genome per month, but this genome is about seven times smaller. However, such comparisons of mutation rates are not very meaningful and say little about the relative evolutionary mutability of the viruses.

When asked whether the mutations made the current spread possible in the first place, the scientist explained that, to his knowledge, there were no indications of this, but that it could not be ruled out. Most of the mutations would “probably have no dramatic effects”.

As Neher describes, many laboratories have now analyzed the genome of monkeypox cases – most of these sequences belonged to the cluster described in the study.