Viruses are considered by some biologists to be a life form, because they carry genetic material, reproduce, and evolve through natural selection, although they lack some key characteristics, …

Dec 3, 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 …

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 …

1 day 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 cells …

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. If …

3 days ago · RSV usually peaks soon Respiratory syncytial virus is a common cause of cold-like symptoms. But it can be dangerous for infants and the elderly, and is known for filling hospitals …

Viruses are microscopic biological agents that invade living hosts and infect their bodies by reproducing within their cell tissue. Viruses are tiny infectious agents that rely on living cells to …

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 …

3 days ago · The majority of flu viruses collected and analyzed by American laboratories during this respiratory virus season have been subclade K, a variant of a flu strain called H3N2, which …

Viruses are typically described as obligate intracellular parasites, acellular infectious agents that require the presence of a host cell in order to multiply.