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21,300 | The booster is equipped with four electrically actuated grid fins, each with a mass of . The grid fins are unevenly spaced for more pitch control and can only rotate in the roll axis. Between the grid fins are Super Heavy's hardpoints, which are used for lifting and catching by the mechanical arms on the integration to... | https://en.wikipedia.org/wiki?curid=59118602 |
21,301 | Starship is a second stage or long-duration spacecraft, and forms the upper part of the rocket. The spacecraft is tall and has a dry mass of less than . Starship's payload volume is about , slightly larger than the International Space Station's pressurized volume, and can be enlarged with a -tall extension. By refuelin... | https://en.wikipedia.org/wiki?curid=59118602 |
21,302 | Starship has a total propellant capacity of across main tanks and header tanks. The header tanks are better insulated due to their position and are reserved for use to flip and land the spacecraft following reentry. About of hydraulic fluid is used for the spacecraft's operations. At the aft end of the Starship spacecr... | https://en.wikipedia.org/wiki?curid=59118602 |
21,303 | The spacecraft has four body flaps to control the spacecraft's orientation and help dissipate energy during atmospheric entry, composed of two forward flaps and two aft flaps. Under the forward flaps, hardpoints are used for lifting and catching the spacecraft via mechanical arms. The flap's hinges are sealed with meta... | https://en.wikipedia.org/wiki?curid=59118602 |
21,304 | Starship's heat shield, composed of thousands of hexagonal black tiles, is designed to be used many times without between-flight maintenance. The tiles are made of silica and are more uniform in shape than the Space Shuttle's heat shield tiles. They are attached with pins rather than glued, with small gaps in between t... | https://en.wikipedia.org/wiki?curid=59118602 |
21,305 | For satellite launch, Starship will possess a large cargo door which will open to release payloads and close upon reentry, instead of a more conventional jettisonable nose-cone fairing. Payloads are integrated directly into Starship's payload bay instead of a cleanroom, which necessitates purging the payload bay with t... | https://en.wikipedia.org/wiki?curid=59118602 |
21,306 | Crewed Starship vehicles would replace the cargo bay with a pressurized crew section and would have a life support system. For long-duration missions, such as crewed flights to Mars, SpaceX describes the interior as potentially including "private cabins, large communal areas, centralized storage, solar storm shelters, ... | https://en.wikipedia.org/wiki?curid=59118602 |
21,307 | Starship is a crewed lunar lander variant of the Starship vehicle that is extensively modified for landing, operation, and takeoff from the lunar surface. It features modified landing legs, a body-mounted solar array, a set of thrusters mounted mid-body to assist with final landing and takeoff, two airlocks, and an ele... | https://en.wikipedia.org/wiki?curid=59118602 |
21,308 | To reach higher-energy targets—such as geosynchronous orbit, the Moon, and Mars—Starship may be refueled by docking with separately launched Starship propellant tanker spacecraft. A Starship propellant depot can be used to cache methane and oxygen on-orbit, and will be used by Starship HLS. | https://en.wikipedia.org/wiki?curid=59118602 |
21,309 | The payload will first integrate onto Starship at a separate facility and then roll out to the launch site. After Super Heavy and Starship are stacked onto a launch mount by lifting from hardpoints, they will be loaded with propellant via the quick disconnect arm and mount. Roughly four hundred truck deliveries are nee... | https://en.wikipedia.org/wiki?curid=59118602 |
21,310 | After two minutes, at an altitude of , Super Heavy is going to cut off its engines and release the interstage latches, causing the rocket stages to separate. The booster will then flip its orientation and ignite its engines briefly. As the booster returns to the launch site via a controlled descent, similar to the Falc... | https://en.wikipedia.org/wiki?curid=59118602 |
21,311 | Meanwhile, the Starship spacecraft accelerates to orbital velocity. Once in orbit, the spacecraft can be refueled by one or more tanker variant Starships, increasing the spacecraft's capacity. To land on bodies without an atmosphere such as the Moon, Starship would turn on its engines and thrusters to slow down. To lan... | https://en.wikipedia.org/wiki?curid=59118602 |
21,312 | Near touchdown, the Raptor engines will fire, using propellant from the header tanks, causing the spacecraft to flip back to a vertical orientation. At this stage, Raptor engines' gimbaling, throttle, and reaction control system's firing will help precisely maneuver the craft. A pseudospectral optimal control algorithm... | https://en.wikipedia.org/wiki?curid=59118602 |
21,313 | If Starship's rocket stages land on a pad, a mobile hydraulic lift will then move them to a transporter vehicle. If the rocket stages land on a floating platform, they will be transported by a barge to a port and move the rest of the distance by road. After recovery, Super Heavy and Starship will either be positioned o... | https://en.wikipedia.org/wiki?curid=59118602 |
21,314 | Starship's reusability is expected to reduce launch costs, expanding space access to more payloads and entities. Musk has stated that a Starship orbital launch will eventually cost $1 million (or $10 per kilogram). However, Eurospace's director of research Pierre Lionnet stated that Starship's launch cost will likely b... | https://en.wikipedia.org/wiki?curid=59118602 |
21,315 | Starship is also planned to launch the second satellite generation of SpaceX's Starlink constellation, used for delivering global high-speed internet. A space analyst at financial services company Morgan Stanley stated development of Starship and Starlink are intertwined, with Starship launch capacity enabling cheaper ... | https://en.wikipedia.org/wiki?curid=59118602 |
21,316 | As of 19 August 2022, the Superbird-9 communication satellite is Starship's first and only known contract for externally made commercial satellites. The satellite weighs dry mass and plans to launch in 2024 to a geostationary orbit. Also in the near term, the crewed variant of the spacecraft can be used for space touri... | https://en.wikipedia.org/wiki?curid=59118602 |
21,317 | In the farther future, Starship may host point-to-point flights, coined "Earth to Earth" by SpaceX, traveling anywhere on Earth in under one hour. SpaceX president and chief operating officer Gwynne Shotwell predicted point-to-point travel could become cost-competitive with conventional business class flights. Contrari... | https://en.wikipedia.org/wiki?curid=59118602 |
21,318 | Starship's capability may make future space probes more experimental. For example, large space telescopes such as the Large Ultraviolet Optical Infrared Surveyor can be launched on Starship, allowing researchers to detect Earth-like exoplanets. Starship may also be able to launch probes orbiting Neptune or Io, or large... | https://en.wikipedia.org/wiki?curid=59118602 |
21,319 | However, there are differing opinions about how Starship's low launch cost will affect future science payloads' cost. According to Waleed Abdalati, former NASA Chief Scientist, the low launch cost will make satellite replacement cheaper and enable more ambitious missions for budget-limited programs. Though according to... | https://en.wikipedia.org/wiki?curid=59118602 |
21,320 | Starship's lunar lander variant, Starship HLS, is critical to the Artemis program, a current NASA human exploration program of the Moon. The lander is accompanied by Starship tankers and Starship propellant depot variants. The tankers transfer propellant to a depot until it is full, then the depot fuels Starship HLS. B... | https://en.wikipedia.org/wiki?curid=59118602 |
21,321 | The Starship spacecraft's Mars variant is expected to be able to land on Mars and return to Earth. First, the main spacecraft is launched to low Earth orbit, then gets refueled by around five tanker spacecraft before heading towards Mars. After landed on Mars, the Sabatier reaction is used to create liquid methane and ... | https://en.wikipedia.org/wiki?curid=59118602 |
21,322 | SpaceX and Musk have stated their goal of colonizing Mars to ensure the long-term survival of humanity, with an ambition of sending thousand Starship spacecraft to Mars during a Mars launch window. This goal has been evident since before SpaceX's founding, when Musk in 2001 joined the Mars Society and researched about ... | https://en.wikipedia.org/wiki?curid=59118602 |
21,323 | Musk has made many tentative predictions about Starship's first crewed Mars landing, the most recent one being 2029, made in March 2022. However, some are sceptical that SpaceX will meet the prediction, as the company has not detailed technical plans about Starship's life-support systems, radiation protection, and in-o... | https://en.wikipedia.org/wiki?curid=59118602 |
21,324 | Starbase consists of a manufacturing facility and launch site, and is located at Boca Chica, Texas. Both facilities operate for twenty-four hours a day, and a maximum of 450 full-time employees may be onsite. The site is planned to consist of two launch sites, one payload processing facility, one seven-acre solar farm,... | https://en.wikipedia.org/wiki?curid=59118602 |
21,325 | At McGregor, Texas, the Rocket Development facility tests all Raptor engines. The facility has two main test stands: one horizontal stand for both engine types and one vertical stand for sea-level-optimized rocket engines. Other test stands are used for checking Starship's reaction control thrusters and Falcon's Merlin... | https://en.wikipedia.org/wiki?curid=59118602 |
21,326 | At Florida, a facility at Cocoa purifies silica for Starship heat-shield tiles, producing a slurry which is then shipped to another facility at Cape Canaveral. In the past, workers at this facility constructed the Starship Mk2 prototype in competition with Starbase's crews. Within the state, the Kennedy Space Center is... | https://en.wikipedia.org/wiki?curid=59118602 |
21,327 | Starbase is planned to host two launch sites, named Pad A and B. A launch site at Starbase has large facilities, such as a tank farm, launch pad, and an integration tower. Smaller facilities are present at the launch site: tanks surrounding the area contain methane, oxygen, nitrogen, helium, hydraulic fluid, etc.; subc... | https://en.wikipedia.org/wiki?curid=59118602 |
21,328 | An integration tower or launch tower consists of steel truss sections, a lightning rod on top, and a pair of mechanical arms that can lift, catch and recover the booster called "Mechazilla". The mechanical arms are attached onto a carriage and controlled by a pulley at the top of the tower. The pulley is linked to a wi... | https://en.wikipedia.org/wiki?curid=59118602 |
21,329 | Since 2021, the company is constructing a Starship launch pad in Cape Canaveral, Florida in Kennedy Space Center's Launch Complex 39A, which is currently used to launch Crew Dragon capsules to the International Space Station. SpaceX plans to make a separate pad at 39A's north, named Launch Complex 49. Because of Launch... | https://en.wikipedia.org/wiki?curid=59118602 |
21,330 | "Phobos" and "Deimos" are the names of two Starship offshore launch platforms, both of which were in renovation as of March 2022. Before being purchased from Valaris plc in June 2020, they were nearly-identical oil platforms named Valaris 8501 and Valaris 8500. Their main decks are long by wide; their four columns are ... | https://en.wikipedia.org/wiki?curid=59118602 |
21,331 | Reception to Starship's development among local communities has been mixed, especially from cities near the Starbase spaceport. Proponents of SpaceX's arrival said the company would provide money, education, and job opportunities to the country's poorest areas. Fewer than one-fifth of those twenty-five or older in the ... | https://en.wikipedia.org/wiki?curid=59118602 |
21,332 | Opponents of the development said the company encourages Brownsville's gentrification, with an ever-increasing property valuation. Though Starbase had been originally planned to launch Falcon rockets when the original environmental assessment was completed in 2014, the site in 2019 was subsequently used to develop Star... | https://en.wikipedia.org/wiki?curid=59118602 |
21,333 | A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. | https://en.wikipedia.org/wiki?curid=19167679 |
21,334 | Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, more than 9,000 virus species have been described in detail of the millions of types of viruses in the environment. Viruses are found in almost... | https://en.wikipedia.org/wiki?curid=19167679 |
21,335 | When infected, a host cell is often forced to rapidly produce thousands of copies of the original virus. When not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles, or virions, consisting of (i) the genetic material, i.e., long molecules of DNA or RNA that... | https://en.wikipedia.org/wiki?curid=19167679 |
21,336 | The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogou... | https://en.wikipedia.org/wiki?curid=19167679 |
21,337 | Viruses spread in many ways. One transmission pathway is through disease-bearing organisms known as vectors: for example, viruses are often transmitted from plant to plant by insects that feed on plant sap, such as aphids; and viruses in animals can be carried by blood-sucking insects. Many viruses, including influenza... | https://en.wikipedia.org/wiki?curid=19167679 |
21,338 | Viral infections in animals provoke an immune response that usually eliminates the infecting virus. Immune responses can also be produced by vaccines, which confer an artificially acquired immunity to the specific viral infection. Some viruses, including those that cause HIV/AIDS, HPV infection, and viral hepatitis, ev... | https://en.wikipedia.org/wiki?curid=19167679 |
21,339 | The word is from the Latin neuter referring to poison and other noxious liquids, from the same Indo-European base as Sanskrit , Avestan , and ancient Greek (all meaning 'poison'), first attested in English in 1398 in John Trevisa's translation of Bartholomeus Anglicus's "De Proprietatibus Rerum". "Virulent", from Latin... | https://en.wikipedia.org/wiki?curid=19167679 |
21,340 | Viruses are found wherever there is life and have probably existed since living cells first evolved. The origin of viruses is unclear because they do not form fossils, so molecular techniques are used to investigate how they arose. In addition, viral genetic material occasionally integrates into the germline of the hos... | https://en.wikipedia.org/wiki?curid=19167679 |
21,341 | In the past, there were problems with all of these hypotheses: the regressive hypothesis did not explain why even the smallest of cellular parasites do not resemble viruses in any way. The escape hypothesis did not explain the complex capsids and other structures on virus particles. The virus-first hypothesis contraven... | https://en.wikipedia.org/wiki?curid=19167679 |
21,342 | The evidence for an ancestral world of RNA cells and computer analysis of viral and host DNA sequences are giving a better understanding of the evolutionary relationships between different viruses and may help identify the ancestors of modern viruses. To date, such analyses have not proved which of these hypotheses is ... | https://en.wikipedia.org/wiki?curid=19167679 |
21,343 | Scientific opinions differ on whether viruses are a form of life or organic structures that interact with living organisms. They have been described as "organisms at the edge of life", since they resemble organisms in that they possess genes, evolve by natural selection, and reproduce by creating multiple copies of the... | https://en.wikipedia.org/wiki?curid=19167679 |
21,344 | Viruses display a wide diversity of sizes and shapes, called 'morphologies'. In general, viruses are much smaller than bacteria and more than a thousand bacteriophage viruses would fit inside an "Escherichia coli" bacterium's cell. Many viruses that have been studied are spherical and have a diameter between 20 and 300... | https://en.wikipedia.org/wiki?curid=19167679 |
21,345 | A complete virus particle, known as a "virion", consists of nucleic acid surrounded by a protective coat of protein called a capsid. These are formed from protein subunits called capsomeres. Viruses can have a lipid "envelope" derived from the host cell membrane. The capsid is made from proteins encoded by the viral ge... | https://en.wikipedia.org/wiki?curid=19167679 |
21,346 | The poxviruses are large, complex viruses that have an unusual morphology. The viral genome is associated with proteins within a central disc structure known as a nucleoid. The nucleoid is surrounded by a membrane and two lateral bodies of unknown function. The virus has an outer envelope with a thick layer of protein ... | https://en.wikipedia.org/wiki?curid=19167679 |
21,347 | Mimivirus is one of the largest characterised viruses, with a capsid diameter of 400 nm. Protein filaments measuring 100 nm project from the surface. The capsid appears hexagonal under an electron microscope, therefore the capsid is probably icosahedral. In 2011, researchers discovered the largest then known virus in s... | https://en.wikipedia.org/wiki?curid=19167679 |
21,348 | Some viruses that infect Archaea have complex structures unrelated to any other form of virus, with a wide variety of unusual shapes, ranging from spindle-shaped structures to viruses that resemble hooked rods, teardrops or even bottles. Other archaeal viruses resemble the tailed bacteriophages, and can have multiple t... | https://en.wikipedia.org/wiki?curid=19167679 |
21,349 | An enormous variety of genomic structures can be seen among viral species; as a group, they contain more structural genomic diversity than plants, animals, archaea, or bacteria. There are millions of different types of viruses, although fewer than 7,000 types have been described in detail. As of January 2021, the NCBI ... | https://en.wikipedia.org/wiki?curid=19167679 |
21,350 | A virus has either a DNA or an RNA genome and is called a DNA virus or an RNA virus, respectively. The vast majority of viruses have RNA genomes. Plant viruses tend to have single-stranded RNA genomes and bacteriophages tend to have double-stranded DNA genomes. | https://en.wikipedia.org/wiki?curid=19167679 |
21,351 | Viral genomes are circular, as in the polyomaviruses, or linear, as in the adenoviruses. The type of nucleic acid is irrelevant to the shape of the genome. Among RNA viruses and certain DNA viruses, the genome is often divided up into separate parts, in which case it is called segmented. For RNA viruses, each segment o... | https://en.wikipedia.org/wiki?curid=19167679 |
21,352 | A viral genome, irrespective of nucleic acid type, is almost always either single-stranded (ss) or double-stranded (ds). Single-stranded genomes consist of an unpaired nucleic acid, analogous to one-half of a ladder split down the middle. Double-stranded genomes consist of two complementary paired nucleic acids, analog... | https://en.wikipedia.org/wiki?curid=19167679 |
21,353 | For most viruses with RNA genomes and some with single-stranded DNA (ssDNA) genomes, the single strands are said to be either positive-sense (called the 'plus-strand') or negative-sense (called the 'minus-strand'), depending on if they are complementary to the viral messenger RNA (mRNA). Positive-sense viral RNA is in ... | https://en.wikipedia.org/wiki?curid=19167679 |
21,354 | Genome size varies greatly between species. The smallest—the ssDNA circoviruses, family "Circoviridae"—code for only two proteins and have a genome size of only two kilobases; the largest—the pandoraviruses—have genome sizes of around two megabases which code for about 2500 proteins. Virus genes rarely have introns and... | https://en.wikipedia.org/wiki?curid=19167679 |
21,355 | In general, RNA viruses have smaller genome sizes than DNA viruses because of a higher error-rate when replicating, and have a maximum upper size limit. Beyond this, errors when replicating render the virus useless or uncompetitive. To compensate, RNA viruses often have segmented genomes—the genome is split into smalle... | https://en.wikipedia.org/wiki?curid=19167679 |
21,356 | Viruses undergo genetic change by several mechanisms. These include a process called antigenic drift where individual bases in the DNA or RNA mutate to other bases. Most of these point mutations are "silent"—they do not change the protein that the gene encodes—but others can confer evolutionary advantages such as resis... | https://en.wikipedia.org/wiki?curid=19167679 |
21,357 | Segmented genomes confer evolutionary advantages; different strains of a virus with a segmented genome can shuffle and combine genes and produce progeny viruses (or offspring) that have unique characteristics. This is called reassortment or 'viral sex'. | https://en.wikipedia.org/wiki?curid=19167679 |
21,358 | Genetic recombination is the process by which a strand of DNA (or RNA) is broken and then joined to the end of a different DNA (or RNA) molecule. This can occur when viruses infect cells simultaneously and studies of viral evolution have shown that recombination has been rampant in the species studied. Recombination is... | https://en.wikipedia.org/wiki?curid=19167679 |
21,359 | Viral populations do not grow through cell division, because they are acellular. Instead, they use the machinery and metabolism of a host cell to produce multiple copies of themselves, and they assemble in the cell. When infected, the host cell is forced to rapidly produce thousands of copies of the original virus. | https://en.wikipedia.org/wiki?curid=19167679 |
21,360 | Their life cycle differs greatly between species, but there are six basic stages in their life cycle: | https://en.wikipedia.org/wiki?curid=19167679 |
21,361 | "Attachment" is a specific binding between viral capsid proteins and specific receptors on the host cellular surface. This specificity determines the host range and type of host cell of a virus. For example, HIV infects a limited range of human leucocytes. This is because its surface protein, gp120, specifically intera... | https://en.wikipedia.org/wiki?curid=19167679 |
21,362 | "Penetration" or "viral entry" follows attachment: Virions enter the host cell through receptor-mediated endocytosis or membrane fusion. The infection of plant and fungal cells is different from that of animal cells. Plants have a rigid cell wall made of cellulose, and fungi one of chitin, so most viruses can get insid... | https://en.wikipedia.org/wiki?curid=19167679 |
21,363 | "Uncoating" is a process in which the viral capsid is removed: This may be by degradation by viral enzymes or host enzymes or by simple dissociation; the end-result is the releasing of the viral genomic nucleic acid. | https://en.wikipedia.org/wiki?curid=19167679 |
21,364 | "Replication" of viruses involves primarily multiplication of the genome. Replication involves the synthesis of viral messenger RNA (mRNA) from "early" genes (with exceptions for positive-sense RNA viruses), viral protein synthesis, possible assembly of viral proteins, then viral genome replication mediated by early or... | https://en.wikipedia.org/wiki?curid=19167679 |
21,365 | "Assembly" – Following the structure-mediated self-assembly of the virus particles, some modification of the proteins often occurs. In viruses such as HIV, this modification (sometimes called maturation) occurs after the virus has been released from the host cell. | https://en.wikipedia.org/wiki?curid=19167679 |
21,366 | "Release" – Viruses can be released from the host cell by lysis, a process that kills the cell by bursting its membrane and cell wall if present: this is a feature of many bacterial and some animal viruses. Some viruses undergo a lysogenic cycle where the viral genome is incorporated by genetic recombination into a spe... | https://en.wikipedia.org/wiki?curid=19167679 |
21,367 | The genetic material within virus particles, and the method by which the material is replicated, varies considerably between different types of viruses. | https://en.wikipedia.org/wiki?curid=19167679 |
21,368 | The range of structural and biochemical effects that viruses have on the host cell is extensive. These are called 'cytopathic effects'. Most virus infections eventually result in the death of the host cell. The causes of death include cell lysis, alterations to the cell's surface membrane and apoptosis. Often cell deat... | https://en.wikipedia.org/wiki?curid=19167679 |
21,369 | Some viruses cause no apparent changes to the infected cell. Cells in which the virus is latent and inactive show few signs of infection and often function normally. This causes persistent infections and the virus is often dormant for many months or years. This is often the case with herpes viruses. | https://en.wikipedia.org/wiki?curid=19167679 |
21,370 | Viruses are by far the most abundant biological entities on Earth and they outnumber all the others put together. They infect all types of cellular life including animals, plants, bacteria and fungi. Different types of viruses can infect only a limited range of hosts and many are species-specific. Some, such as smallpo... | https://en.wikipedia.org/wiki?curid=19167679 |
21,371 | A novel virus is one that has not previously been recorded. 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. It can be an emergent virus, one that represents a new virus, but it can also be an ext... | https://en.wikipedia.org/wiki?curid=19167679 |
21,372 | Classification seeks to describe the diversity of viruses by naming and grouping them on the basis of similarities. In 1962, André Lwoff, Robert Horne, and Paul Tournier were the first to develop a means of virus classification, based on the Linnaean hierarchical system. This system based classification on phylum, clas... | https://en.wikipedia.org/wiki?curid=19167679 |
21,373 | The ICTV developed the current classification system and wrote guidelines that put a greater weight on certain virus properties to maintain family uniformity. A unified taxonomy (a universal system for classifying viruses) has been established. Only a small part of the total diversity of viruses has been studied. As of... | https://en.wikipedia.org/wiki?curid=19167679 |
21,374 | The general taxonomic structure of taxon ranges and the suffixes used in taxonomic names are shown hereafter. As of 2021, the ranks of subrealm, subkingdom, and subclass are unused, whereas all other ranks are in use. | https://en.wikipedia.org/wiki?curid=19167679 |
21,375 | The Nobel Prize-winning biologist David Baltimore devised the Baltimore classification system. The ICTV classification system is used in conjunction with the Baltimore classification system in modern virus classification. | https://en.wikipedia.org/wiki?curid=19167679 |
21,376 | The Baltimore classification of viruses is based on the mechanism of mRNA production. Viruses must generate mRNAs from their genomes to produce proteins and replicate themselves, but different mechanisms are used to achieve this in each virus family. Viral genomes may be single-stranded (ss) or double-stranded (ds), RN... | https://en.wikipedia.org/wiki?curid=19167679 |
21,377 | Examples of common human diseases caused by viruses include the common cold, influenza, chickenpox, and cold sores. Many serious diseases such as rabies, Ebola virus disease, AIDS (HIV), avian influenza, and SARS are caused by viruses. The relative ability of viruses to cause disease is described in terms of virulence.... | https://en.wikipedia.org/wiki?curid=19167679 |
21,378 | Viruses have different mechanisms by which they produce disease in an organism, which depends largely on the viral species. Mechanisms at the cellular level primarily include cell lysis, the breaking open and subsequent death of the cell. In multicellular organisms, if enough cells die, the whole organism will start to... | https://en.wikipedia.org/wiki?curid=19167679 |
21,379 | Some viruses can cause lifelong or chronic infections, where the viruses continue to replicate in the body despite the host's defence mechanisms. This is common in hepatitis B virus and hepatitis C virus infections. People chronically infected are known as carriers, as they serve as reservoirs of infectious virus. In p... | https://en.wikipedia.org/wiki?curid=19167679 |
21,380 | Viral epidemiology is the branch of medical science that deals with the transmission and control of virus infections in humans. Transmission of viruses can be vertical, which means from mother to child, or horizontal, which means from person to person. Examples of vertical transmission include hepatitis B virus and HIV... | https://en.wikipedia.org/wiki?curid=19167679 |
21,381 | Horizontal transmission is the most common mechanism of spread of viruses in populations. Horizontal transmission can occur when body fluids are exchanged during sexual activity, by exchange of saliva or when contaminated food or water is ingested. It can also occur when aerosols containing viruses are inhaled or by in... | https://en.wikipedia.org/wiki?curid=19167679 |
21,382 | Epidemiology is used to break the chain of infection in populations during outbreaks of viral diseases. Control measures are used that are based on knowledge of how the virus is transmitted. It is important to find the source, or sources, of the outbreak and to identify the virus. Once the virus has been identified, th... | https://en.wikipedia.org/wiki?curid=19167679 |
21,383 | A pandemic is a worldwide epidemic. The 1918 flu pandemic, which lasted until 1919, was a category 5 influenza pandemic caused by an unusually severe and deadly influenza A virus. The victims were often healthy young adults, in contrast to most influenza outbreaks, which predominantly affect juvenile, elderly, or other... | https://en.wikipedia.org/wiki?curid=19167679 |
21,384 | Although viral pandemics are rare events, HIV—which evolved from viruses found in monkeys and chimpanzees—has been pandemic since at least the 1980s. During the 20th century there were four pandemics caused by influenza virus and those that occurred in 1918, 1957 and 1968 were severe. Most researchers believe that HIV ... | https://en.wikipedia.org/wiki?curid=19167679 |
21,385 | Several highly lethal viral pathogens are members of the "Filoviridae". Filoviruses are filament-like viruses that cause viral hemorrhagic fever, and include ebolaviruses and marburgviruses. Marburg virus, first discovered in 1967, attracted widespread press attention in April 2005 for an outbreak in Angola. Ebola viru... | https://en.wikipedia.org/wiki?curid=19167679 |
21,386 | Except for smallpox, most pandemics are caused by newly evolved viruses. These "emergent" viruses are usually mutants of less harmful viruses that have circulated previously either in humans or other animals. | https://en.wikipedia.org/wiki?curid=19167679 |
21,387 | Severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) are caused by new types of coronaviruses. Other coronaviruses are known to cause mild infections in humans, so the virulence and rapid spread of SARS infections—that by July 2003 had caused around 8,000 cases and 800 deaths—was unexpec... | https://en.wikipedia.org/wiki?curid=19167679 |
21,388 | A related coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2), thought to have originated in bats, emerged in Wuhan, China in November 2019 and spread rapidly around the world. Infections with the virus caused the COVID-19 pandemic that started in 2020. Unprecedented restrictions in peacetime were... | https://en.wikipedia.org/wiki?curid=19167679 |
21,389 | Viruses are an established cause of cancer in humans and other species. Viral cancers occur only in a minority of infected persons (or animals). Cancer viruses come from a range of virus families, including both RNA and DNA viruses, and so there is no single type of "oncovirus" (an obsolete term originally used for acu... | https://en.wikipedia.org/wiki?curid=19167679 |
21,390 | Hepatitis viruses can develop into a chronic viral infection that leads to liver cancer. Infection by human T-lymphotropic virus can lead to tropical spastic paraparesis and adult T-cell leukaemia. Human papillomaviruses are an established cause of cancers of cervix, skin, anus, and penis. Within the "Herpesviridae", K... | https://en.wikipedia.org/wiki?curid=19167679 |
21,391 | The body's first line of defence against viruses is the innate immune system. This comprises cells and other mechanisms that defend the host from infection in a non-specific manner. This means that the cells of the innate system recognise, and respond to, pathogens in a generic way, but, unlike the adaptive immune syst... | https://en.wikipedia.org/wiki?curid=19167679 |
21,392 | RNA interference is an important innate defence against viruses. Many viruses have a replication strategy that involves double-stranded RNA (dsRNA). When such a virus infects a cell, it releases its RNA molecule or molecules, which immediately bind to a protein complex called a dicer that cuts the RNA into smaller piec... | https://en.wikipedia.org/wiki?curid=19167679 |
21,393 | When the adaptive immune system of a vertebrate encounters a virus, it produces specific antibodies that bind to the virus and often render it non-infectious. This is called humoral immunity. Two types of antibodies are important. The first, called IgM, is highly effective at neutralising viruses but is produced by the... | https://en.wikipedia.org/wiki?curid=19167679 |
21,394 | Antibodies can continue to be an effective defence mechanism even after viruses have managed to gain entry to the host cell. A protein that is in cells, called TRIM21, can attach to the antibodies on the surface of the virus particle. This primes the subsequent destruction of the virus by the enzymes of the cell's prot... | https://en.wikipedia.org/wiki?curid=19167679 |
21,395 | A second defence of vertebrates against viruses is called cell-mediated immunity and involves immune cells known as T cells. The body's cells constantly display short fragments of their proteins on the cell's surface, and, if a T cell recognises a suspicious viral fragment there, the host cell is destroyed by 'killer T... | https://en.wikipedia.org/wiki?curid=19167679 |
21,396 | Not all virus infections produce a protective immune response in this way. HIV evades the immune system by constantly changing the amino acid sequence of the proteins on the surface of the virion. This is known as "escape mutation" as the viral epitopes escape recognition by the host immune response. These persistent v... | https://en.wikipedia.org/wiki?curid=19167679 |
21,397 | Because viruses use vital metabolic pathways within host cells to replicate, they are difficult to eliminate without using drugs that cause toxic effects to host cells in general. The most effective medical approaches to viral diseases are vaccinations to provide immunity to infection, and antiviral drugs that selectiv... | https://en.wikipedia.org/wiki?curid=19167679 |
21,398 | Vaccination is a cheap and effective way of preventing infections by viruses. Vaccines were used to prevent viral infections long before the discovery of the actual viruses. Their use has resulted in a dramatic decline in morbidity (illness) and mortality (death) associated with viral infections such as polio, measles,... | https://en.wikipedia.org/wiki?curid=19167679 |
21,399 | Antiviral drugs are often nucleoside analogues (fake DNA building-blocks), which viruses mistakenly incorporate into their genomes during replication. The life-cycle of the virus is then halted because the newly synthesised DNA is inactive. This is because these analogues lack the hydroxyl groups, which, along with pho... | https://en.wikipedia.org/wiki?curid=19167679 |
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