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VirusTotal is a service that allows you to scan files, domains, IPs and URLs for malware and other threats. You can also share your submissions with the security community and access various tools, API, reports and intelligence.
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Learn about viruses, submicroscopic infectious agents that replicate only inside living cells. Explore their diversity, transmission, evolution, and interactions with hosts and antiviral drugs.
- Overview
- Definition
- Host range and distribution
A virus is an infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria.
What are viruses made of?
A virus particle is made up of genetic material housed inside a protein shell, or capsid. The genetic material, or genome, of a virus may consist of single-stranded or double-stranded DNA or RNA and may be linear or circular in form.
What size are viruses?
Most viruses vary in diameter from 20 nanometres (nm; 0.0000008 inch) to 250–400 nm. The largest viruses measure about 500 nm in diameter and are about 700–1,000 nm in length.
Are all viruses spherical in shape?
Viruses occupy a special taxonomic position: they are not plants, animals, or prokaryotic bacteria (single-cell organisms without defined nuclei), and they are generally placed in their own kingdom. In fact, viruses should not even be considered organisms, in the strictest sense, because they are not free-living—i.e., they cannot reproduce and carry on metabolic processes without a host cell.
All true viruses contain nucleic acid—either DNA (deoxyribonucleic acid) or RNA (ribonucleic acid)—and protein. The nucleic acid encodes the genetic information unique for each virus. The infective, extracellular (outside the cell) form of a virus is called the virion. It contains at least one unique protein synthesized by specific genes in the nucleic acid of that virus. In virtually all viruses, at least one of these proteins forms a shell (called a capsid) around the nucleic acid. Certain viruses also have other proteins internal to the capsid; some of these proteins act as enzymes, often during the synthesis of viral nucleic acids. Viroids (meaning “viruslike”) are disease-causing organisms that contain only nucleic acid and have no structural proteins. Other viruslike particles called prions are composed primarily of a protein tightly complexed with a small nucleic acid molecule. Prions are very resistant to inactivation and appear to cause degenerative brain disease in mammals, including humans.
Viruses are quintessential parasites; they depend on the host cell for almost all of their life-sustaining functions. Unlike true organisms, viruses cannot synthesize proteins, because they lack ribosomes (cell organelles) for the translation of viral messenger RNA (mRNA; a complementary copy of the nucleic acid of the nucleus that associates with ribosomes and directs protein synthesis) into proteins. Viruses must use the ribosomes of their host cells to translate viral mRNA into viral proteins.
Viruses are also energy parasites; unlike cells, they cannot generate or store energy in the form of adenosine triphosphate (ATP). The virus derives energy, as well as all other metabolic functions, from the host cell. The invading virus uses the nucleotides and amino acids of the host cell to synthesize its nucleic acids and proteins, respectively. Some viruses use the lipids and sugar chains of the host cell to form their membranes and glycoproteins (proteins linked to short polymers consisting of several sugars).
The true infectious part of any virus is its nucleic acid, either DNA or RNA but never both. In many viruses, but not all, the nucleic acid alone, stripped of its capsid, can infect (transfect) cells, although considerably less efficiently than can the intact virions.
The virion capsid has three functions: (1) to protect the viral nucleic acid from digestion by certain enzymes (nucleases), (2) to furnish sites on its surface that recognize and attach (adsorb) the virion to receptors on the surface of the host cell, and, in some viruses, (3) to provide proteins that form part of a specialized component that enables the virion to penetrate through the cell surface membrane or, in special cases, to inject the infectious nucleic acid into the interior of the host cell.
Logic originally dictated that viruses be identified on the basis of the host they infect. This is justified in many cases but not in others, and the host range and distribution of viruses are only one criterion for their classification. It is still traditional to divide viruses into three categories: those that infect animals, plants, or bacteria.
Virtually all plant viruses are transmitted by insects or other organisms (vectors) that feed on plants. The hosts of animal viruses vary from protozoans (single-celled animal organisms) to humans. Many viruses infect either invertebrate animals or vertebrates, and some infect both. Certain viruses that cause serious diseases of animals and humans are carried by arthropods. These vector-borne viruses multiply in both the invertebrate vector and the vertebrate host.
Mar 29, 2023 · Learn what viruses are, how they infect hosts and cause diseases, and what types of viruses exist. Find out how viruses reproduce, how they are classified and how they can be treated.
Learn what viruses are, how they infect cells, and how they vary in structure and genome. Explore the diversity and evolution of viruses with examples and interactive features.
- No, because they are not living things. Good question, though.
- Another aspect is that we are constantly running into new viruses. Why? Viruses can be divided into two groups: one group of viruses spreads only b...
- This is an excellent question and is the subject of current scientific research! Short answer — we don't know and the answer may be different for d...
- I think "chemical unit" is the wrong phrase to use here. A simple stone or pebble at a microscopic scale can be compared to a rough mountain range...
- It would be possible, but not practical. Having free roaming proteins in your body to attract viruses is like having pools of acid in the ocean to...
- No, viruses do *not* have that trait of living organisms - growth and development. Viruses only reproduce - if they find host (cell). Do viruses di...
- No the scientific community is split on whether a virus is alive or not but freezing a sample will actually preserve it. Researchers have found and...
- Viral infections are hard to treat because viruses live inside your body's cells. They are "protected" from medicines, which usually move through y...
- So they can attach to the host as stealthily as possible. Too large of a pathogen could alert the immune system to a threat before the virus even g...
- From What I can gather, according to this:https://www.ncbi.nlm.nih.gov/pubmed/203115, Hydrogen peroxide can make viruses inactive.
Learn about the virus that causes COVID-19, how it spreads, and how to protect yourself and others. Find the latest information, advice, and resources from the World Health Organization.
Mar 13, 2020 · Once a person is infected with a virus, their body becomes a reservoir of virus particles which can be released in bodily fluids – such as by coughing and sneezing – or by shedding skin or in...
