has there been human-to-human transmission of the monkeypox virus since 2017?

The first results genetic analysis of the strain of the smallpox from the monkey collected in Portugal revealed that the strain which infected 780 people outside Africa was, at the time of writing, phylogenetically related to that of 2017-2019, isolated in Singapore, Israel in Nigeria and the United Kingdom .

Today, two specialists in virus evolution from the University of Edinburgh in Scotland provided genetic analysis much more detailed and which provides keys to understanding why this strain of monkeypox virus spreads between humans as well.

47 mutations in the 2022 monkeypox strain

Between the strain of 2022 and its most recent ancestors of 2017-2019, there are 47 nucleotides of difference. That is to say, in the space of a few years, the virus has accumulated 47 mutations. That’s a lot when you know that the mutation rate of smallpoxanother orthopoxvirus, is one or two mutations per year.

This unusual number of mutations could be a sign that the monkeypox virus has adapted to humans. A hypothesis under study at this very moment and which does not yet give a clear answer. In fact, the majority of the mutations observed are due to the action of a enzyme antiviral drug, Apobec3, which acts against viruses by introducing mutations into their DNA in the hope of rendering them non-viable and blocking their replication.

Apobec3 causes deaminations, it mainly targets TC base duos, transforming them into TT (or their equivalent AG to AA), and GG, converting them to AG (or their equivalent AA to AC). Among the 47 mutations identified, 42 are TC to TT deaminations and 3 from GG to AG. The remaining two are the result of other mechanisms.

The enzyme Apobec3 is therefore the main source of mutations in the genome virus from monkey pox. This observation raises several questions. Did it act in non-human reservoirs before emerging in humans? The Apobec anti-viral system exists in rodents but it does not leave the same signatures in the genome of the viruses on which it acts.

Long-standing human-to-human circulation?

Are these mutations the witness of an adaptation over several years of the virus to the human being? On this point, scientists suggest that “ the pattern we see in these MPXV (monkeypoxvirus) genomes since 2017 indicates replication in humans and that the inheritance of specific changes that occurred between 2017 and 2018 and then in viruses from 2022 onwards means that there is had sustained human-to-human transmission since at least 2017 “.

In 2017, cases of monkey pox, animals and humans, were reported in several Central and West African countries, including several thousand a year in the Democratic Republic of the Congo. These were mostly animal-to-human transmissions. If there was sustained human-to-human transmission, as scientists believe, before the current situation, it went unnoticed. Further results are awaited to understand why there are as many cases of monkeypox outside of Africa.

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