What type of pathogens are viruses?

Viruses are categorized as non-living particles that replicate inside host cells. Unlike bacteria or fungi, which are classified as living organisms because they can metabolize and reproduce independently, viruses lack the cellular structure necessary for independent life. They cannot carry out metabolic processes on their own and rely entirely on invading a host’s cells to replicate and propagate.

Once inside a host cell, viruses take over the cell's machinery to produce new virus particles. This dependency on host cells distinguishes viruses clearly from multicellular and unicellular organisms, which can live and reproduce independently in various environments. Thus, the classification of viruses as non-living particles that replicate within host cells captures their unique biological nature.