A mutated version of the virus at the origin of this epidemic?

Thousands of confirmed cases of monkeypox around the world, new contaminations received every day, and a virus that is raising more and more fears on the globe. On Thursday, the World Health Organization (WHO) called on countries to be vigilant and transparent in the face of this outbreak of an unusual scale, and brought together international experts to determine whether the situation constitutes a “health emergency”. “. of international concern”, as is the case for the Covid-19 pandemic.

An unusual upsurge

in early May, an abnormal upsurge is caused outside the countries of West and Central Africa, where the virus is endemic but usually generates relatively few cases there. Since the three cases of monkeypox identified a little over six weeks ago in the United Kingdom, none of which had recently traveled outside the country, the contaminations have been increasing.

“More than 3,200 confirmed cases of monkeypox and one death have been reported to WHO in 48 countries, including Nigeria,” WHO Director General Tedros Adhanom Ghebreyesus said. In France, 330 cases have been filed, according to the latest figures from Public Health France.

“In addition, since the beginning of the year, nearly 1,500 suspected cases (…) and around 70 deaths have been reported in Central Africa, mainly in the Democratic Republic of Congo, but also in the Central African Republic and Cameroon”, continued the head of the WHO. “We did not expect to have such a large number of cases. And it is a bit difficult to see what is the tip of the iceberg”, in particular because screening is not easy, said Philippe Duneton, executive director of Unitaid, an organization which helps poor countries to prevent, diagnose and treat diseases.

47 mutations retained in the current strain

In the current outbreak, of which Europe is so far the global epicenter, the majority of cases so far involved men who have sex with men (MSM). Although transmission can occur through close contact, such as sexual intercourse, smallpox is not a sexually transmitted infection.

How can this epidemic emerging from its endemic cradle be explained? This is the answer that researchers from the Institute of Evolutionary Biology at the University of Edinburgh in Scotland are trying to find, who have analyzed the monkeypox genome and uncovered an abnormally high number of mutations. Unlike Covid-19, which is an RNA virus and is capable of carrying dozens of mutations, monkeypox is an enveloped double-stranded DNA virus from the Poxviridae family. And in this family, to which classic smallpox belongs, the mutation rate of the virus is rather one to two mutations per year. However, by comparing the current strain of monkeypox to the strains that improved contamination between 2017 and 2019, the researchers discovered no less than 47 mutations in the new version.

Among them, 42 bear the distinct signature of an antiviral enzyme called “Apobec3”, which is supposed to help the immune system force the virus to make mistakes when it replicates, and thus cause it to self-destruct. While monkeypox was originally “considered a zoonotic virus with limited human-to-human transmission, this long branch [de mutations] may be proof of an adaptation of the virus to humans,” say the researchers. And now, it is to infected humans that it is recommended to avoid pets so that they do not transmit the virus to them.

“Sustained human-to-human transmission” for several years

Known in humans since 1970, monkey pox, or “simian orthopoxvirus”, is nevertheless a disease considered rare, caused by a virus transmitted to humans by infected animals. Thus, many cases in Africa have been attributed to contact with wild animals. Or, in the current outbreak, human-to-human transmission is at the forefront. So much so that the WHO considers it likely that the actual number of cases is higher, and considers that the virus must have already been circulating before the current outbreak – possibly since 2017 – without its transmission being detected.

A hypothesis that is supported by the analysis made by the Scottish researchers, who estimated that “the pattern we see in these monkeypox genomes since 2017 indicates replication in humans, and that the inheritance of the specific changes that have occurred between 2017 and 2018, and then in viruses from 2022, means that there has been sustained human-to-human transmission, since at least 2017”.

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