During the first year of life, the human gut is filled with bacteria and viruses that can affect an individual's health. A recent study identified as many as 10,000 virus species, many of them unknown, in the faeces of newborns.
An infant’s intestine in the first year of life is an almost completely unexplored universe. Now the mystery is a little less obscure thanks to a study published in the scientific journal Nature Microbiology by researchers from Danish, Canadian and French universities.
The authors wanted to focus not so much on the bacteria, which had already been the subject of thousands of studies, but on the viruses present. They analysed stool samples from 647 children in the group (a cohort, in technical terms) that had been set up in 2010 for the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC). The researchers carefully examined the materials that had been collected and stored during the first 12 months of the infants’ lives, and thus managed to identify an incredible 10,000 virus species in their faeces, from 248 viral families, only 16 of which were already known. The other 232 were all described and named after the child in which they were isolated (they therefore have names like Sylvesterviridae, Rigmorviridae, Lauraviridae and Natasjaviridae).
Researchers discovered that in 90% of cases, these are not viruses that are dangerous to humans, but bacterial viruses, better known as bacteriophages (or more simply phages). This type of microorganism has been known for a long time, but it has attracted increasing interest in recent years, both as a target for potential therapies and for its role in the complex balance of the microbiota (the set of microorganisms that populate the intestine and other parts of our body).
Two different types of virus
There are generally, two types of bacteriophages: those known as virulent, and those, which are more common, known as temperate. The first kind reproduce within the bacteria they infect and produce 30-100 new viral particles in each cell, causing the death of the bacterium itself. However, temperate bacteriophages integrate their own genetic material into that of the infected bacterium, making their 'victim' more resistant and, for example, teaching it to metabolise nutrients more efficiently.
While the former are of interest for possible therapeutic applications, the latter are interesting for the transfer of genetic information and hybridisation between different species- phenomena that have yet to be completely understood, but are vital for studying the evolution of life and, probably, of many diseases.
The remaining 10% of the viruses found were micro-organisms typically adapted to human cells, and potentially pathogenic, although not all dangerous viruses become so. Indeed, it is thought that in the vast majority of cases, they serve to train the immune system to recognise a threat, part of the continually developing abilities that are typical of the first post-natal months.
Influence on adult diseases
As the researchers point out, what happens during these complex interactions may determine the health of the child, and also that of the adult the child will become. This is why mapping is an essential first step.
In the meantime, the authors are continuing both the in-depth study of the basic mechanisms of some of the viruses and phages they isolated, and to study their relationships with typical childhood diseases like asthma or ADHD.
