Diff: Virus
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A '''virus''' is a small infectious agent that can replicate only inside a living cell. Viruses contain genetic material, either DNA or RNA, packaged in a protective protein coat. Some also have a lipid envelope taken from a host-cell membrane. |
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Viruses are microscopic infectious agents that occupy a unique position between living and non-living entities. They are composed of genetic material enclosed in a protein coat and lack the cellular machinery necessary for independent metabolism. Viruses are known for their ability to replicate and spread within host cells, often causing diseases in various organisms, including humans, animals, plants, and even bacteria. |
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Viruses infect animals, plants, fungi, bacteria, archaea, and other organisms. They are central to infectious disease, ecology, evolution, molecular biology, vaccine development, and biotechnology. |
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== Structure and Composition == |
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Viruses consist of genetic material, either DNA or RNA, surrounded by a protein coat called a capsid. Some viruses also possess an outer lipid envelope derived from the host cell's membrane. The capsid protects the genetic material and aids in the virus's attachment to host cells. The genetic material carries the instructions for viral replication and hijacks the host cell's machinery to produce new virus particles. |
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== Structure == |
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A complete virus particle outside a cell is called a virion. The basic parts are: |
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== Replication and Life Cycle == |
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The life cycle of a virus involves several stages: |
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* A genome made of DNA or RNA. |
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* A protein coat called a capsid. |
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* In some viruses, an envelope containing lipids and viral proteins. |
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* Surface proteins that help attach to host cells. |
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# Attachment: The virus attaches to specific receptors on the surface of a host cell. |
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# Penetration: The virus or its genetic material enters the host cell. |
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# Replication and Transcription: The virus's genetic material is replicated and transcribed within the host cell, leading to the production of new viral components. |
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# Assembly: New virus particles are assembled using the replicated genetic material and synthesized proteins. |
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# Release: New virus particles are released from the host cell, often causing cell lysis or other forms of cellular damage. |
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The genome may be single-stranded or double-stranded, segmented or unsegmented, circular or linear. This affects how the virus replicates and how it is classified. |
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== Replication == |
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Viruses do not have the full machinery needed for independent metabolism or reproduction. They must enter a host cell and use that cell's machinery to make viral components. |
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A simplified replication cycle includes: |
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* Attachment to a suitable host-cell receptor. |
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* Entry into the cell or delivery of the genome. |
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* Release of the viral genome inside the cell. |
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* Genome replication and viral protein production. |
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* Assembly of new virions. |
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* Release by cell lysis, budding, exocytosis, or another route. |
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Different viruses use different strategies. For example, retroviruses use reverse transcriptase, many DNA viruses replicate in the nucleus, and many RNA viruses replicate in the cytoplasm. |
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== Classification == |
== Classification == |
Viruses are classified based on several factors, including their genetic material, structure, and mode of replication. The International Committee on Taxonomy of Viruses (ICTV) categorizes viruses into different families, genera, and species. Major virus families include: |
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Viruses are classified by genome type, structure, replication strategy, host range, evolutionary relationships, and taxonomic evidence. The International Committee on Taxonomy of Viruses provides official virus taxonomy resources, including current species lists and taxonomy releases. |
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* Retroviridae: Includes viruses with RNA genomes that replicate using a reverse transcriptase enzyme, such as HIV. |
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* Herpesviridae: Encompasses DNA viruses that cause diseases like herpes and chickenpox. |
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* Picornaviridae: Comprises small RNA viruses responsible for diseases like the common cold and polio. |
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Common broad categories include: |
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== Viral Diseases == |
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Viruses are responsible for a wide range of diseases in humans and other organisms. Some well-known viral diseases include: |
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* DNA viruses. |
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* RNA viruses. |
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* Reverse-transcribing viruses. |
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* Enveloped and non-enveloped viruses. |
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* Animal, plant, fungal, bacterial, and archaeal viruses. |
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* Influenza: Caused by the influenza virus, leading to respiratory infections. |
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* COVID-19: Caused by the novel coronavirus SARS-CoV-2, resulting in a global pandemic. |
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* HIV/AIDS: Caused by the human immunodeficiency virus, leading to a weakened immune system. |
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* Measles: Caused by the measles virus, causing fever and rash. |
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* Hepatitis: Caused by various hepatitis viruses, affecting the liver. |
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Virus names and virus species names are not always the same thing. ICTV guidance treats taxonomy as a formal scientific system, while common virus names are often used in medicine and public communication. |
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== Vaccination and Treatment == |
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Vaccination is a crucial strategy to prevent viral infections. Vaccines stimulate the immune system to produce antibodies against specific viruses, providing immunity. Antiviral medications are also used to treat some viral infections by inhibiting viral replication. However, developing antiviral drugs can be challenging due to the complex nature of viral life cycles. |
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== Viral Disease == |
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Many viruses cause disease, but many others do not cause obvious disease in a particular host. Disease depends on the virus, the host, immune status, exposure route, dose, and tissue affected. |
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== Importance in Research == |
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Studying viruses has led to significant advancements in molecular biology, immunology, and virology. Viruses have served as model systems to understand fundamental cellular processes and mechanisms of genetic regulation. Research on viruses has also paved the way for gene therapy, genetic engineering, and novel drug development. |
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Human viral diseases include influenza, measles, COVID-19, HIV infection, viral hepatitis, chickenpox, shingles, rabies, dengue, norovirus infection, and many common respiratory infections. |
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== Viruses and Evolution == |
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Viruses play a role in the evolution of organisms by influencing genetic diversity and adaptation. Horizontal gene transfer, a process in which genetic material is transferred between organisms, can occur through viral infections, contributing to genetic variation and evolutionary innovation. |
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Viral disease can be caused by: |
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== Conclusion == |
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Viruses, though simple in structure, have a profound impact on the natural world and human health. Their ability to cause diseases and manipulate host cells has driven extensive research and innovation in science and medicine. |
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* Direct cell damage. |
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* Immune-mediated injury. |
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* Persistent infection. |
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* Cancer-promoting changes in infected cells. |
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* Secondary complications, such as bacterial infection after a viral illness. |
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== See Also == |
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== Prevention == |
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Prevention depends on the virus. Measures can include vaccination, ventilation, hand hygiene, safer sex, blood screening, vector control, isolation during infectious periods, protective equipment, and animal vaccination. |
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* [[Microorganisms]] |
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Vaccination is one of the most important tools against viral disease. Some vaccines prevent infection very effectively. Others mainly reduce severe disease, hospitalisation, or death. |
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== Treatment == |
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Antibiotics do not treat viral infections. They act against bacteria, not viruses. Antiviral medicines are available for some viral infections, including HIV, influenza, herpesviruses, hepatitis B, hepatitis C, and COVID-19, but many viral infections are managed with supportive care. |
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Antiviral treatment works best when it targets a specific step in the viral life cycle, such as entry, genome replication, protein processing, or release. Resistance can develop, especially when viruses mutate rapidly or treatment pressure is incomplete. |
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== Role in Science == |
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Viruses have shaped modern biology. They have helped researchers understand genes, transcription, translation, cancer biology, immunity, and cell signalling. Viral tools are used in gene therapy, vaccines, protein production, and laboratory delivery systems. |
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Viruses also affect evolution. They can move genetic material between organisms, apply selection pressure to host populations, and leave viral sequences in host genomes over long periods. |
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== See Also == |
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* [[Virology]] |
* [[Virology]] |
* [[Vaccination]] |
* [[Vaccination]] |
* [[AntiVirus]] |
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* [[Bacteria]] |
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== References == |
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* [https://www.ncbi.nlm.nih.gov/books/NBK8174/ NCBI Bookshelf: Structure and classification of viruses] |
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* [https://ictv.global/ ICTV: Official virus taxonomy resources] |
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* [https://ictv.global/taxonomy ICTV: Current virus taxonomy release] |
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* [https://www.cdc.gov/vaccines/by-disease/index.html CDC: Vaccines by disease] |
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[[Category:Medicine]] |
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[[Category:Virology]] |
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[[Category:Microbiology]] |