What exactly is the human virome, and why should you care?
The human virome is the collection of all viruses—both those that infect human cells (eukaryotic viruses) and those that infect bacteria (bacteriophages)—that reside in and on your body. It is astonishingly abundant: an estimated 10^13 viral particles inhabit a single human, outnumbering bacteria by about ten to one [7]. This viral community is not a random assortment; it is shaped by your age, diet, geography, and even antibiotic use [5]. For instance, the gut virome in industrialized populations is dominated by a group of bacteriophages called CrAss-like phages, which are rare in non-industrialized groups [5]. This matters because these viruses do not just sit idly—they actively interact with your bacterial microbiome and your immune system, influencing health and disease [4][7].
A key point is that the virome is highly personalized. A 2022 study of skin viromes from 42 individuals found that each person's viral signature was unique and stable over six months, enough to be used for forensic identification [8]. This individuality means that how the virome affects your health may be different from how it affects someone else's.
How does the virome influence your risk of disease?
The virome can both protect and harm, depending on the context. In the gut, bacteriophages help regulate bacterial populations—for example, by killing harmful bacteria or by transferring genes that confer antibiotic resistance [1][4]. A 2026 study on laying hens with fatty liver hemorrhagic syndrome found that the gut virome in sick birds had significantly lower diversity and richness (P < 0.05) and carried a higher diversity of antibiotic resistance genes, suggesting that virome disruption contributes to metabolic disease [1]. Similarly, in children with diarrhea, the gut virome shifted away from healthy bacteriophages (like Microviridae and Caudovirales) toward disease-causing viruses (like Adenoviridae and Caliciviridae) [3]. This indicates that a balanced virome is important for gut health.
The virome also plays a role in chronic diseases. A 2023 review highlighted that phages can influence cancer risk through lysogeny—where a virus integrates into a bacterial genome and alters bacterial behavior, potentially promoting chronic inflammation or cancer [6]. In the respiratory tract, the virome in healthy individuals is characterized by low viral abundance and high variability, but in chronic respiratory diseases, this balance is disrupted [10]. For example, anelloviruses dominate the upper airways in health, while herpesviruses and Streptococcus phages are more common in the lower airways [10]. These shifts can modulate host immunity and disease progression.
What are the biggest unknowns about the virome's impact?
Despite progress, the field is still in its infancy. A major challenge is that most viral sequences in a typical sample—often called 'viral dark matter'—cannot be matched to known viruses [5][7]. This means we are only seeing a fraction of the picture. A 2024 perspective outlined ten computational hurdles, including the lack of a universal marker gene for viruses and their low abundance in samples, which makes detection difficult [2]. For example, the human virome is so diverse and dynamic that even advanced sequencing methods miss many viruses [2].
Another gap is understanding what a 'healthy' virome looks like. The National Institutes of Health Human Virome Program, launched in 2023, aims to define the virome across diverse populations and lifespans, but this work is ongoing [9]. For now, we know that virome composition varies by body site (gut, skin, oral, respiratory) and that disruptions are linked to disease, but we cannot yet say what the optimal virome is for a given person [4][9]. This limits our ability to use the virome for personalized medicine, though early efforts like fecal virome transplantation for Clostridioides difficile infection show promise [4][5].
Sources used in this answer
Characterization of the gut phageome and functional genes carried by phages in laying hens with fatty liver hemorrhagic syndrome.
In laying hens with fatty liver disease, the gut virome showed significantly lower diversity and richness, and carried a higher diversity of antibiotic resistance genes, linking virome disruption to metabolic disease [1].
Ten computational challenges in human virome studies
Ten computational challenges hinder virome research, including the lack of a universal viral marker gene and low viral abundance, which limit detection and analysis [2].
Viral metagenomics of the gut virome of diarrheal children with Rotavirus A infection
In children with diarrhea, the gut virome shifted away from healthy bacteriophages (Microviridae, Caudovirales) toward disease-causing viruses (Adenoviridae, Caliciviridae), showing virome composition changes with disease [3].
The gut virome: A new microbiome component in health and disease
The gut virome is highly heterogeneous across populations and linked to geography, diet, and lifestyle; it interacts with bacteria and host to influence health, and shows promise for diagnostics and therapies like fecal virome transplantation [4].
The human gut virome: composition, colonization, interactions, and impacts on human health
The gut virome is established at birth, stable in adulthood, and highly individual; it is dominated by CrAss-like phages in industrialized populations, and its disruption is linked to disease [6].
Human virome: Implications in cancer
The human virome is implicated in cancer through phage regulation of bacterial flora via lysogeny, which can increase susceptibility to chronic inflammation and cancer [10].
The human virome: assembly, composition and host interactions
The human virome consists of approximately 10^13 viral particles per individual, with great heterogeneity; most sequence data remains unidentified 'viral dark matter' [11].
The application of the skin virome for human identification
Skin virome analysis from 42 individuals identified 59 stable viral biomarkers that were significantly different across subjects (P < 0.001), demonstrating potential for forensic human identification [12].
Oral virome in health and disease.
The oral virome is largely unexplored; the NIH Human Virome Program aims to characterize commensal viruses across the lifespan to understand health and disease associations [13].
The Human Respiratory Virome in Health and Disease: Interactions, Dysbiosis, and Methodological Challenges
The respiratory virome in healthy individuals has low biomass and high temporal variability, with Anelloviruses in upper airways and Streptococcus phages in lower airways; disruptions are linked to chronic respiratory diseases [15].