Having older siblings may influence the mixture of viruses in babies’ guts, known as the gut virome.
While there has been a wealth of research on how gut bacteria influence our health, we know much less about the importance of viruses in the gut, which can have good and bad effects.
At birth, the guts of most babies are devoid of viruses, but in the first few years of life, viruses that infect gut cells directly and those that infect gut bacteria – known as bacteriophages – start to colonise the intestines. These viruses enter the gut along with food or are ingested when babies interact with other people and their surroundings.
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To better understand the early influences on children’s gut viromes, and both at the University of Copenhagen, and their colleagues analysed faecal samples from 645 infants aged 1 living in Copenhagen, collected as part of a previous study on asthma.
To do this, they filtered out viruses from stool samples before sequencing the DNA genomes of the viruses, revealing more than 16,000 different viral species from the babies’ guts, of which over 90 per cent were bacteriophages. The researchers then compared the composition of infants’ gut viromes with a range of environmental factors the babies had been exposed to, according to survey responses.
They found that having older siblings was linked to an increased diversity of viruses in babies’ guts and greater variation in the abundance of different gut viruses.
“This makes sense – babies with older siblings will often be exposed to a greater range of bacteria and viruses that may, for example, come from nursery or school,” says Deng.
Eating eggs later than average in the first year of life was also linked to greater differences in the abundance of different gut viruses. But rather than there being a direct effect of eggs on the virome, it is more likely that when a baby first eats eggs correlates with other lifestyle and dietary factors that affect gut viruses, says Stokholm.
Babies who lived in a rural rather than urban area had a greater abundance of viruses that infect certain bacteria, such as those found in yogurt, but the reason for this link is also unclear, says Stokholm.
Further research is needed to establish exactly how changes in the virome may influence people’s health as babies and later in life.
“It’s been proposed for many years that it’s good to have a wide diversity of gut bacteria, but with gut viruses, this is totally new land, so it’s difficult to say whether it’s good or bad to have higher diversity or a more even distribution of different viral species,” says Stokholm.
“This is an exciting study as it includes a very large sample set and includes detailed environmental influences that have not yet been examined in relation to the infant gut virome,” says at Washington University in St. Louis, Missouri.
As the infant virome sets the stage for the adult virome, it may influence our future health, says Holtz. In the future, altering infants’ exposure to environmental factors could help them develop an optimal virome, says Holtz.
However, this study only focuses on viruses with a DNA genome, rather than an RNA genome, leaving much to be discovered, says Holtz. What’s more, the participants were mainly white, so further research on more diverse populations is needed, she says.
bioRxiv
