• One study found that babies' diapers contained thousands of previously undescribed virus species, according to our partner The Conversation.
  • These viruses mostly belong to the category of "bacteriophages", which make up the largest part of our microbiome and contribute to its "good health".
  • This analysis was conducted by Evelien Adriaenssens, a researcher in intestinal viruses and viromes at the Quadram Institute Bioscience in Norwich (UK).
  • Written in English, this article was translated by The Conversation.

For five years, an international team of scientists from Denmark, Canada and France studied the faeces of 647 Danish babies. The analysis of the contents of these thousands of layers revealed an astonishing discovery: they contained some 10,000 species of viruses, ten times more than the number of bacterial species present in the same children...

And that's not all: most of these viruses had never been described before!

This finding is likely to worry many readers and parents... Viruses have never really had a good reputation, and the situation has not improved in recent years. But what many don't know is that the overwhelming majority of viruses don't make people sick – they don't infect humans or animals at all.

The viruses in question here are mainly "bacteriophages": that is to say, they are viruses that exclusively infect bacteria; They are the ones that make up the bulk of our microbiome. And these are bacteriophages that were found in abundance in the babies' diapers – about 90% of the viruses found in the study were bacteria-killers.

Where do they come from? From the gut microbiota... The human gut microbiome is indeed a complex collection of microorganisms, including bacteria and archaea (two large groups of single-celled organisms without a nucleus), microbial eukaryotes (cells with a nucleus, like ours) and viruses.

The viral component of the gut microbiome, or "virome," consists primarily of bacteriophages that contribute to maintaining a healthy and diverse global microbiome. Because it is not the presence of microbes that is problematic, but an imbalance between its different components...

An atlas to store them all

If finding that babies' diapers are reserves of virus is interesting, for specialists it is only the beginning of labor. They then looked to find out how many of these 10,000 viruses were known and unknown... and how best to describe this unprecedented viral diversity in an accessible form. Which is complex.

Presenting them all in a huge table would be a rather boring (and impractical) read. Instead, they created an "atlas of the diversity of viruses in the infant's gut DNA," in which they grouped and classified the viruses into new families and orders – based on the degree of similarity of their genomes. In doing so, they identified 248 families, of which only 16 were already known.

The researchers proposed naming the 232 newly identified virus families after the children who participated in the study – such as "Sylvesterviridae", "Rigmorviridae" and "Tristanviridae", etc.

An interactive version of the atlas is available online.

Babies have a unique set of viruses

What's interesting about bacteriophages and other viruses in the gut is that each person has a unique "assortment" of them, with very little overlap between two people.

What's more, while each gut virome is unique, it's also stable over time in adults: meaning you carry the same set of viruses with you as you age. But things are different at the beginning of life. Right after birth, a baby has a virome is very different from the one he will have as an adult. It will take years to build up and stabilize its final virome.

It was therefore also interesting to compare the approximately 10,000 viruses identified in the study to large collections of reference viromes of healthy adults... This is how the researchers found that only 800 of these viruses had already been discovered before!

This confirms that after birth, the first bacteriophages to colonize the gastrointestinal tract (digestive tract) of babies during their first months of life will not remain: these "baby bacteriophages" will be gradually and largely replaced by "adult bacteriophages". There will thus be a massive overhaul of the virome, which will be done in a specific way for everyone!

As the authors of the study recall, the establishment of its intestinal microbiome during its first years of life will play an essential role in the maturation of the infant's immune system.

A great intestinal replacement

This replacement could be partially related to the evolution of the bacteria that these viruses infect. For example, Bacteroides, Faecalibacterium and Bifidobacterium are the main predicted hosts for baby bacteriophages.

As an expert on bacteriophages and their hosts, I would like to emphasize the importance of Bifidobacterium species for infant health. These bacteria contribute to the digestion of breast milk and are therefore essential at the beginning of life; On the other hand, they are less abundant with age. It is therefore logical that viruses that infect Bifidobacterium are more present in babies and less in adults.

Conversely, the most abundant group of adult intestinal bacteriophages, that of members of the order Crassvirales, is not as prevalent in the stool of babies. So they acquire them later, as they get older.


With the addition of these 10,000 new species of viruses, belonging to many previously unknown families, from a single group of several hundred Danish babies, it is clear that there is more we don't know about the virome than we do know. The scientific community is working on it, one layer at a time...

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This article is produced by The Conversation and hosted by 20 Minutes.

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