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.

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 that cells do to …

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 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 …

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.

5 days ago · Limited COVID-19 surveillance data are hampering vaccination and health strategies, researchers say.

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 …

The mechanism by which a virus is transmitted depends on several things, including which organisms the virus is able to infect, which types of cells in those organisms the virus can …

Jun 26, 2024 · A virus is a small infectious agent that can only replicate inside the cells of another organism.

Fundamentally, then, a virus is a package of genetic information protected by a protein shell for delivery into a host cell to be expressed and replicated. The virus eventually takes over the cell …