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Viruses Live in The Guts of Healthy Babies

Yes, even healthy newborns have a diversity of viruses in the gut - this is their virome (community of viruses), and it undergoes changes over time. In fact, the entire infant microbiome (community of microbes) is highly dynamic and the composition of bacteria, viruses and bacteriophages changes with age. One interesting finding is that initially newborn babies have a lot of bacteriophages (viruses that infect bacteria), but that these decline over the first two years of age. From Medical Xpress:

Viruses flourish in guts of healthy babies

Bacteria aren't the only nonhuman invaders to colonize the gut shortly after a baby's birth. Viruses also set up house there, according to new research at Washington University School of Medicine in St. Louis. All together, these invisible residents are thought to play important roles in human health.The study, published online Sept. 14 in Nature Medicine, reports data from eight healthy infants and is one of the first surveys of viruses that reside in the intestine. The investigators analyzed stool samples to track how the babies' bacterial gut microbiomes and viromes changed over the first two years of life.

"We are just beginning to understand the interplay between all the different types of life within our gut," said senior author Lori R. Holtz, MD, assistant professor of pediatrics. "They are not stand-alone communities. We also are seeing that the environment of the infant gut is extremely dynamic, which differs from the relative stability that has been shown in adults."The earliest stool samples were taken at 1-4 days of life, and even at this early time point, Holtz noted, viruses were present

"We were surprised that right from the beginning quite a diversity of viruses was found in the gut," said Holtz, also a pediatric gastroenterologist who treats patients at St. Louis Children's Hospital. "It prompts the question—where do these viruses come from? We don't know yet whether diet, method of the baby's delivery or other environmental influences play a role."

Analyzing genomic material in the stool samples, the researchers noted that some of the viruses they identified are known to infect cells of the human host, but others actually infect the bacteria. In fact, the researchers found that the kinds of viruses that infect bacteria, not human cells, were the most rich and diverse earliest in an infant's life and then their numbers declined. They also showed that strains of bacteria did the opposite, starting out with low numbers early and becoming more diverse as the babies grew into their toddler years.

The investigators suspect that the changes in population dynamics they observed in these viruses and bacteria are caused by a predator-prey relationship. The viruses that exclusively kill bacteria are called bacteriophage, literally "bacteria eater." The early diversity of bacteriophage means lots of predators with no prey. Since bacteriophage can't survive without their bacterial prey, the high bacteriophage numbers quickly go down. Faced with few predators, bacteria are then free to flourish and colonize the gut. "The predator-prey dynamic is still a hypothesis at this point," Holtz said. 

The researchers also observed a relatively large diversity of a type of virus that infects human cells called anellovirus. Anelloviruses are of interest to researchers because they appear to reflect a person's immune status, with more viruses present when the immune system is weaker"One child had at least 47 anellovirus strains at the 12-month sampling," Holtz said. "It's important to remember that these are healthy children living in the community. 

The researchers also noted that almost all of the anelloviruses identified in this study were previously unknown. Such data, originating from only eight babies in St. Louis, hints at the size and difficulty of the task of even determining a healthy baseline for the virome. Such a baseline is required before scientists can understand what roles gut viromes may play in conditions like obesity, diabetes, colitis and Crohn's disease."At this point, we're just trying to establish what is normal," Holtz said.

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