It can be a virus that is isolated from its natural reservoir or isolated as the result of spread to an animal or human host where the virus had not been identified before.

Mar 29, 2023 · A virus is a small piece of genetic information in a “carrying case” — a protective coating called a capsid. Viruses aren’t made up of cells, so they don’t have all the equipment …

Oct 13, 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 …

2 days ago · A Washington state man has been infected with a strain of bird flu previously only detected in animals and never before in humans.

Apr 12, 2025 · When a virus enters the body, the innate immune system reacts first. This non-specific defense includes barriers like skin, as well as cells that engulf and destroy invaders.

2 days ago · A virus is an infectious microbe consisting of a segment of nucleic acid (either DNA or RNA) surrounded by a protein coat. A virus cannot replicate alone; instead, it must infect …

Oct 19, 2023 · In humans, viruses can cause many diseases. For example, the flu is caused by the influenza virus. Typically, viruses cause an immune response in the host, and this kills the …