A recent genetic study suggests that the monkeypox virus mutated at a much faster rate than expected, likely going through a period of “accelerated evolution”. How to explain such a phenomenon?
The Ile-de-France Regional Health Agency (ARS) reported this weekend the first confirmed case of monkey pox in a child in the region. Until then, the virus had only affected adults. The latest report shows 330 confirmed cases of infection in France. More broadly, the virus is believed to have infected more than 3,500 people in 48 countries since its detection outside Africa last May.
Historically, monkeypox was transmitted through close skin contact with open skin lesions, contaminated equipment, bodily fluids, or projected respiratory droplets. However, the speed at which this pathogen appears to spread suggests that it may infect its hosts a little differently. Some specialists then suggested that new mutations could be a possible cause.
In a recent study published in the journal Nature Medicine, researchers have tested this hypothesis. To do this, they collected a fifteen samples of viruses and reconstructs their genetic information. To their surprise, the researchers then discovered that the actual mutation rate was six to twelve times higher than expected.
An accelerated evolution
Concretely, the virus would carry approximately fifty new mutations not seen in previous strains detected from 2018 to 2019. But researchers generally don’t expect such viruses to gain more than one or two mutations each year.
In theory, as a large double-stranded DNA virus, this pathogen is indeed much more capable of correcting replication errors than an RNA virus. This means that the strain currently at the center of concern should have accumulated only a handful of mutations since it began circulating in 2018. For the study authors, these new genetic data reveal a “ potential human adaptation“. Several identified mutations indeed carry telltale clues that they may have emerged as a result of the virus coming into contact with the human immune system.
A family of anti-virus enzymes called APOBEC3 is particularly singled out. These enzymes attack viruses by forcing them to make mistakes when copying their genetic code. This type of approach usually causes the virus to break down. If not, then a virus can pick up some mutations in its genetic code. It could be that these types of battles happened repeatedly and brought the monkeypox virus to capture many mutations in a short time.
A course still uncertain
According to the study, the mutation rate of the virus began to increase in 2018. In the meantime, it is possible that the virus has been circulating in humans at low levels. It’s also possible that the virus spread among animals in non-endemic countries without us noticing, before suddenly swinging into humans this year.
For now, the virus remains relatively harmless. Remember that strains can be classified into two clades (or lineages). One is from West Africa, the other from the Congo Basin. Viruses in each clade have different mortality rates. The West African clade has a mortality rate of about 1%, while the second has a rate of 10%. The current epidemic appears to be caused by the West African clade.
While a direct treatment for monkeypox has not yet been tested, doctors give patients antiviral drugs and antibodies taken from people immunized with the smallpox vaccine.
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