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What makes a virus different?

A virus is best understood as a biological replication system packaged for movement between host cells. Its genome carries information, while the surrounding virion structure protects that genome and helps determine entry into a host cell. The supplied evidence shows that there is no single universal viral design: bacteriophage FLiP has a circular 9,174-nucleotide single-stranded DNA genome, an internal lipid membrane, and an icosahedral capsid about 60 nm wide. Its capsid protein has a double-β-barrel fold resembling structures found in some double-stranded DNA viruses, illustrating that structural relationships can cross genome categories. Virus structure and evolution

How viruses interact with hosts

Replication is not merely a property of the viral genome; it also depends on host-cell context. In cultured human-cell systems, infections by several negative-sense RNA viruses produced virus-associated host-transcriptome signatures that machine-learning models could classify using host expression and k-mer features, even when viral sequences were not used. However, the study used only two immortalized cell lines, selected timepoints, and an in-vitro setting, so clinical generalization remains uncertain. Host responses to viral infection

Viruses as ecosystems, not only pathogens

Many viruses infect bacteria and coexist within microbial communities. In a 6,090-sample analysis of adult stool metagenomes, a computational pipeline detected viral operational taxonomic units and identified two reproducible but weakly separated gut-virome community states; viral features improved disease-classification performance in some datasets. These observations support ecological and diagnostic relevance, but they are observational and catalog-dependent: they do not show that viruses caused the associated health states. Gut virome ecology

Confidence: high for the broad description of viruses as diverse genome-and-particle systems that replicate in hosts; moderate for claims about health associations and genome-agnostic classification because the supplied studies have important model, catalog, and observational limitations. The most decisive missing information for a general theory of viruses is broader comparative evidence across viral groups, hosts, environments, and independently replicated experiments.