The research, led by Peng Zhao, Mengyuan Chen and Ying Kang under the corresponding authorship of Yongfeng Hu and Fan Yang at the NHC Key Laboratory of Systems Biology of Pathogens, part of the Chinese Academy of Medical Sciences and Peking Union Medical College in Beijing, set out to overcome three long-standing obstacles in anellovirus research: fragmented reference datasets, inconsistent taxonomic annotation, and pronounced geographic underrepresentation, particularly of Asian populations. Because most publicly available anellovirus genomes have been sampled from European and North American cohorts, the diversity circulating in other regions has been systematically missed, distorting estimates of global viral richness. To address this gap, the team integrated metagenomic sequencing data from 6,348 Chinese samples with all globally available ANV genomes, constructing an expanded phylogenomic resource that they call the HANVdb Resource.

The scale of the resulting expansion is striking. By harmonizing taxonomy across more than 23,000 accession-level genome records and applying a standardized species-delineation threshold based on ORF1 nucleotide identity, the researchers expanded the represented diversity of human-associated anelloviruses to 771 species-level taxa. Of these, 91 correspond to species formally recognized by the International Committee on Taxonomy of Viruses (ICTV), while a remarkable 680 represent provisional new species (PNS) that had never been catalogued before. That corresponds to an approximately eightfold increase in represented species-level diversity compared with previous reference frameworks, a jump driven largely by the inclusion of Chinese metagenomic data that captured lineages absent from Western-dominated databases.

With this expanded reference in hand, the team turned to the question of what an individual person actually carries. Profiling personal anellomes at species-level and lineage-level resolution revealed extraordinary within-host diversity. The richest individual profile in the analyzed cohorts contained 305 species-level taxa and 2,071 distinct lineages, meaning that a single person can simultaneously host hundreds of anellovirus species and thousands of genetic variants. This level of intra-host diversity rivals, and in many respects exceeds, what has been documented for bacterial communities of the gut microbiome, and it establishes the anellome as one of the most genetically heterogeneous viral communities known to colonize humans.

Beyond raw diversity, the study sought to determine whether the anellome has a stable ecological architecture. By integrating detection frequency, abundance, geographic representation, cross-cohort reproducibility and longitudinal persistence, the researchers identified recurrent “core” anellome components: species and lineages that appear consistently across individuals, cohorts and time points. Longitudinal analysis of publicly available datasets confirmed that these core lineages persist within individuals over years, behaving less like transient infections and more like stable residents of the personal virome. This finding supports the emerging view of anelloviruses as genuine commensals, viruses that establish chronic, largely asymptomatic carriage and whose presence may reflect, and even report on, the immunological state of their host.

That connection to immunity received direct support from the study’s clinical analyses. Several core lineages showed significant inverse associations with CD4 T-cell counts in HIV-infected individuals, meaning that as immune function declined, the abundance of these viral lineages rose. This pattern is consistent with the hypothesis that anellovirus replication is held in check by T-cell-mediated immune control, and it raises the possibility that anellome profiling could serve as a surrogate readout of immune competence. Such a biomarker would be attractive precisely because anelloviruses are so ubiquitous: unlike opportunistic pathogens, they are present in nearly everyone, providing a continuous signal that can be monitored through routine metagenomic sequencing of blood or other specimens.

The study also examined how the anellome is distributed across body compartments. By analyzing paired samples of peripheral blood mononuclear cells (PBMCs) and plasma from the same individuals, the researchers identified compartment-associated differences in diversity, composition and lineage enrichment. Certain lineages were preferentially associated with the cellular fraction, while others dominated the cell-free plasma fraction, indicating that anelloviruses are not passively circulating but instead occupy distinct ecological niches within the bloodstream. This compartmental organization adds a spatial dimension to anellome ecology and suggests that sampling choices, whether one sequences cells or plasma, can materially change the picture of viral diversity obtained.

Among the most technically intriguing findings concerns a specific clade of Betatorquevirus associated with TTMV::RARA, a viral-host gene fusion previously linked to disease. Within the new framework, this clade displayed higher conservation of the ORF2 protein, enrichment of RUNX1 transcription factor motifs, and a PBMC-biased distribution compared with background clades. These molecular signatures hint at mechanistic differences in how this lineage interacts with host cells, potentially including altered replication regulation or integration behavior. While the study stops short of establishing causation, the identification of such lineage-level features provides concrete, testable hypotheses for investigating viral integration-associated disease, an area of growing interest given that anellovirus sequences have been found integrated into tumor genomes in hematologic malignancies.

All of these results are packaged into a reusable analytical infrastructure. The HANVdb Resource includes a curated Human Anellome Reference Dataset v1.0 comprising 10,013 lineages, a standardized pipeline for profiling anellomes from metagenomic sequencing data, and a publicly accessible web interface for downloading reference sequences. The pipeline encompasses reference extraction and clustering, raw-read quality control, host read removal, lineage-level quantification and filtering of low-confidence detections, and the authors validated their assignments through competitive read-level cross-referencing against broad viral databases. Multidimensional scaling and self-organizing map projections of the ORF1 identity matrix provide a discretized map of global anellome sequence space, allowing any new sample to be positioned within the known diversity. The resource, funded by the Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences and the National Natural Science Foundation of China, is released under open access terms to encourage adoption by other groups.

The broader significance of this work lies in reframing how scientists think about the viruses that live within us. Rather than viewing anelloviruses as a diffuse background of incidental infections, the study demonstrates that the human anellome is a structured commensal community, resolvable at species and lineage levels, with stable core members, compartment-specific organization and measurable relationships to host immunity. The eightfold expansion of catalogued diversity underscores how much remains undiscovered, particularly outside well-sampled Western populations, and the strong representation of Asian cohorts in this dataset begins to correct a longstanding geographic bias in virome research. As metagenomic sequencing becomes routine in clinical medicine, tools like the HANVdb Resource may transform anelloviruses from obscure commensals into practical indicators of immune health, and could ultimately clarify their role in the pathogenesis of hematologic disease. For now, the message is clear: the most familiar viruses in the human body are also among the least understood, and mapping them is only just beginning.

Subject of Research: Genomic diversity and ecological structure of the human anellovirus virome (anellome)

Article Title: Defining the genomic and ecological landscapes of the human anellome

Article References: Zhao, P., Chen, M., Kang, Y., Keng, J., Li, X., Feng, B., Sui, H., Dong, J., Sun, L., Jin, Q., Hu, Y., & Yang, F. (2026). Defining the genomic and ecological landscapes of the human anellome. Microbiome. https://doi.org/10.1186/s40168-026-02552-0

Image Credits: AI Generated

DOI: 10.1186/s40168-026-02552-0

Keywords: anellovirus, anellome, human virome, metagenomics, HANVdb, commensal viruses, Betatorquevirus, TTMV::RARA fusion, CD4 T-cell counts, PBMC, plasma, Microbiome journal