The human virome: why viruses could be as important for good health as gut bacteria

By Samuel J. White, Philippe B. Wilson, York St John University

We often hear about the importance of the human microbiome – the vast collection of bacteria and fungi that live on and inside us – when it comes to our health. But there’s another, equally important part of this microbial community that remains far less known: the virome.

The virome consists of all the viruses that inhabit our bodies. This includes those that infect humans cells, bacteriophages (viruses that infect bacteria) and the viruses we aquire from our diet and environment.

Viruses are the most abundant biological entities on Earth, with an estimated 10³¹ viral particles globally and about 10¹³ in each human being.

For centuries, viruses have been seen mainly as causes of disease. But research suggests that viruses influence our health in important ways.

Bacteriophages, for instance, play a crucial role in regulating the bacterial populations in our gut. By keeping harmful bacteria in check, they help prevent conditions such as inflammatory bowel disease (IBD) and obesity.

Certain bacteriophages can also enhance the immune system’s ability to combat bacterial infections. They do this by breaking down the outer membranes of harmful bacteria – releasing antigens that stimulate immune responses.

Some viruses that interact directly with our immune system even help maintain its balance – potentially protecting us from illnesses. For instance, herpesvirus, which causes cold sores and mononucleosis (mono), can alter immune responses. It does this in many ways – such as by promoting the production of specialised immune cells, altering the gene expression of cells and even suppressing anti-inflammatory responses. These changes may potentially reduce risk of developing secondary infections and allergic responses later in life.

Conversely, some viruses might contribute to chronic inflammation by persistently activating immune pathways.

The balance of these interactions is critical. A healthy virome helps fend off infections and support overall health. But an imbalanced virome may contribute to poor health and disease.

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