Babies' gut consists of more than 200 previously unknown viral families within their intestines, which likely plays an important role in protecting children from chronic diseases like asthma and diabetes later on in life, according to scientists.
While it has been known for decades that gut bacteria in young children are vital to protect them from chronic diseases later on in life, the knowledge about the many viruses found there is minimal.
To explore, a team from the University of Copenhagen spent five years studying and mapping the diaper contents of 647 healthy Danish one-year-olds.
"We found an exceptional number of unknown viruses in the faeces of these babies. Not just thousands of new virus species -- but to our surprise, the viruses represented more than 200 families of yet to be described viruses," said Professor Dennis Sandris Nielsen of the Department of Food Science, at the varsity.
"This means that, from early on in life, healthy children are tumbling about with an extreme diversity of gut viruses, which probably have a major impact on whether they develop various diseases later on in life," he added.
In the research paper, published in Nature Microbiology, the team found and mapped a total of 10,000 viral species in the children's faeces -- a number ten times larger than the number of bacterial species in the same children.
These viral species are distributed across 248 different viral families, of which only 16 were previously known.
"Our hypothesis is that, because the immune system has not yet learned to separate the wheat from the chaff at the age of one, an extraordinarily high species richness of gut viruses emerges, and is likely needed to protect against chronic diseases like asthma and diabetes later on in life," said Shiraz Shah, a senior researcher at Copenhagen Prospective Studies on Asthma in Childhood (COPSAC).
Further, the team identified 90 per cent of the viruses as bacterial viruses -- known as bacteriophages. These viruses have bacteria as their hosts and do not attack the children's own cells, meaning that they do not cause disease.
The remaining 10 per cent of viruses are eukaryotic -- that is, they use human cells as hosts. These can be both friends and foes for us.
"It is thought-provoking that all children run around with 10-20 of these virus types that infect human cells. So, there is a constant viral infection taking place, which apparently doesn't make them sick. We just know very little about what's really at play. My guess is that they're important for training our immune system to recognise infections later. But it may also be that they are a risk factor for diseases that we have yet to discover," Sandris Nielsen said.
The researchers have yet to discover where the many viruses in the one-year-olds come from. They presume it is from the environment: via dirty fingers, pets, dirt that kids put in their mouths and other things.
Learning more about the role that bacteria and viruses play in a well-trained immune system, can hopefully lead us to being able to avoid many of the chronic diseases -- from arthritis to depression -- that afflict so many people today, Shah said.