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  1. Virus - Wikipedia

    A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. [1] Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and …

  2. Viruses: Definition, Types, Characteristics & Facts

    Mar 29, 2023 · Viruses are small germs that have to infect a host — like humans, animals, plants — to reproduce. Learn more about types of viruses and how they work.

  3. Virus | Definition, Structure, & Facts | Britannica

    Dec 17, 2025 · Virus, infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria. Viruses possess unique infective properties and thus often …

  4. What Is a Virus? Definition, Structure, and How Viruses Work

    Apr 12, 2025 · A virus’s life truly begins once it meets a host. The process starts with attachment—when a virus latches onto the surface of a suitable cell using specialized proteins. If the virus is a key, the …

  5. Virus - National Human Genome Research Institute

    3 days ago · Virus. Well, we all have learned a lot more about viruses in the last two years with the Covid-19 outbreak/global pandemic. Viruses infect humans. But, in fact, viruses infect many …

  6. Viruses - National Geographic Society

    Oct 19, 2023 · Viruses are tiny infectious agents that invade host cells and cause disease. Although they are harmful, viruses also have interesting technological potential.

  7. What Is a Virus and How Does It Work? - Biology Insights

    A virus is a non-cellular infectious agent, significantly smaller than typical cells, ranging from about 20 to 250 nanometers in size. Its fundamental structure consists of genetic material, which can be either …