Influenza Classification & external resources
TEM of negatively stained influenza virons, magnified approximately 100,000 times
ICD-10	J10., J11.
ICD-9	487
DiseasesDB	6791
MedlinePlus	000080
eMedicine	med/1170  ped/3006
MeSH	D007251

Influenza, commonly known as flu, is an infectious disease of birds and mammals caused by RNA viruses of the family Orthomyxoviridae (the influenza viruses). The name influenza comes from the Italian: influenza, meaning "influence", (Latin: influentia). In humans, common symptoms of the disease are the chills, then fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort.^[1] In more serious cases, influenza causes pneumonia, which can be fatal, particularly in young children and the elderly. Although it is sometimes confused with the common cold, influenza is a much more severe disease and is caused by a different type of virus.^[2] Influenza can produce nausea and vomiting, especially in children,^[1] but these symptoms are more characteristic of the unrelated gastroenteritis, which is sometimes called "stomach flu" or "24-hour flu."^[3] Image File history File links Download high-resolution version (700x743, 81 KB) CDC, CDC Public Health Image Library (PHIL), http://phil. ... A section of a cell of Bacillus subtilis, taken with a Tecnai T-12 TEM. The scale bar is 200nm. ... The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or disease. ... The International Statistical Classification of Diseases and Related Health Problems 10th Revision (ICD-10) is a coding of diseases and signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or diseases, as classified by the World Health Organization (WHO). ... // J00-J99 - Diseases of the respiratory system (J00-J06) Acute upper respiratory infections (J00) Acute nasopharyngitis (common cold) (J01) Acute sinusitis (J02) Acute pharyngitis (J03) Acute tonsillitis (J04) Acute laryngitis and tracheitis (J05) Acute obstructive laryngitis (croup) and epiglottitis (J050) Acute obstructive laryngitis (croup) (J051) Acute epiglottitis (J06) Acute upper... // J00-J99 - Diseases of the respiratory system (J00-J06) Acute upper respiratory infections (J00) Acute nasopharyngitis (common cold) (J01) Acute sinusitis (J02) Acute pharyngitis (J03) Acute tonsillitis (J04) Acute laryngitis and tracheitis (J05) Acute obstructive laryngitis (croup) and epiglottitis (J050) Acute obstructive laryngitis (croup) (J051) Acute epiglottitis (J06) Acute upper... The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or disease. ... The following is a list of codes for International Statistical Classification of Diseases and Related Health Problems. ... The Disease Bold textDatabase is a free website that provides information about the relationships between medical conditions, symptoms, and medications. ... MedlinePlus (medlineplus. ... eMedicine is an online clinical medical knowledge base that was founded in 1996. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... This false-colored electron micrograph shows a malaria sporozoite migrating through the midgut epithelia. ... For other uses, see Bird (disambiguation). ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including milk producing sweat glands, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex... An RNA virus is a virus that either uses RNA as its genetic material, or whose genetic material passes through an RNA intermediate during replication. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus The Orthomyxoviridae are a family of RNA viruses which infect vertebrates. ... For other uses, see Latin (disambiguation). ... This article does not cite its references or sources. ... An analogue medical thermometer showing the temperature of 38. ... ώ:For the noisegrind band, see Sore Throat. ... Myalgia means muscle pain and is a symptom of many diseases and disorders. ... A headache (cephalgia in medical terminology) is a condition of pain in the head; sometimes neck or upper back pain may also be interpreted as a headache. ... Exhaustion redirects here. ... Malaise is a feeling of general discomfort or uneasiness, an out of sorts feeling, often the first indication of an infection or other disease. ... This article is about human pneumonia. ... Acute viral nasopharyngitis, or acute coryza, usually known as the common cold, is a highly contagious, viral infectious disease of the upper respiratory system, primarily caused by picornaviruses or coronaviruses. ... For other uses, see Nausea (disambiguation). ... Emesis redirects here. ... See also Bacterial gastroenteritis and Diarrhea Gastroenteritis is a general term referring to inflammation or infection of the gastrointestinal tract, primarily the stomach and intestines. ...

Typically influenza is transmitted from infected mammals through the air by coughs or sneezes, creating aerosols containing the virus, and from infected birds through their droppings. Influenza can also be transmitted by saliva, nasal secretions, faeces and blood. Infections also occur through contact with these body fluids or with contaminated surfaces. Flu viruses can remain infectious for about one week at human body temperature, over 30 days at 0 °C (32 °F), and for much longer periods at very low temperatures.^[4][5] Most influenza strains can be inactivated easily by disinfectants and detergents.^[6][7][8] Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Horse feces Feces, faeces, or fæces (see spelling differences) is a waste product from an animals digestive tract expelled through the anus (or cloaca) during defecation. ... For the band, see Saliva (band). ... Mucus cells. ... Rabbit feces are usually 0. ... For other uses, see Blood (disambiguation). ... For other uses, see Celsius (disambiguation). ... For other uses, see Fahrenheit (disambiguation). ... This is an article about antimicrobial agents. ... Laundry detergents are just one of many possible uses for detergents Detergent is a compound, or a mixture of compounds, intended to assist cleaning. ...

Flu spreads around the world in seasonal epidemics, killing millions of people in pandemic years and hundreds of thousands in non-pandemic years. Three influenza pandemics occurred in the 20th century and killed tens of millions of people, with each of these pandemics being caused by the appearance of a new strain of the virus in humans. Often, these new strains result from the spread of an existing flu virus to humans from other animal species. A deadly avian strain named H5N1 has posed the greatest risk for a new influenza pandemic since it first killed humans in Asia in the 1990s. Fortunately, this virus has not mutated to a form that spreads easily between people.^[9] In epidemiology, an epidemic (from [[Latin language] epi- upon + demos people) is a disease that appears as new cases in a given human population, during a given period, at a rate that substantially exceeds what is expected, based on recent experience (the number of new cases in the population during... For other uses, see Pandemic (disambiguation). ... In biology, Strain can be used two ways. ... For other uses, see Species (disambiguation). ... Influenza A virus subtype H5N1, also known as A(H5N1) or simply H5N1, is a subtype of the Influenza A virus which can cause illness in humans and many other animal species. ... An influenza pandemic is a large scale epidemic of the influenza virus, such as the 1918 Spanish flu. ... For linguistic mutation, see Apophony. ...

Vaccinations against influenza are usually given to people in developed countries with a high risk of contracting the disease,^[10] and to farmed poultry.^[11] The most common human vaccine is the trivalent influenza vaccine that contains purified and inactivated material from three viral strains. Typically this vaccine includes material from two influenza A virus subtypes and one influenza B virus strain.^[12] A vaccine formulated for one year may be ineffective in the following year, since the influenza virus changes rapidly over time and different strains become dominant. Antiviral drugs can be used to treat influenza, with neuraminidase inhibitors being particularly effective. A vial of the vaccine against influenza. ... World map indicating Human Development Index (as of 2004). ... Model of Influenza Virus from NIH The flu vaccine is a vaccine to protect against the highly variable influenza virus. ... Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. ... Influenzavirus B is a genus in the virus family Orthomyxoviridae. ... Antiviral drugs are a class of medication used specifically for treating viral infections. ... Neuraminidase inhibitors are a class of antiviral drugs, whose mode of action relies on blocking the function of viral neuraminidase protein, thus preventing the virus from budding from the host cell. ...

Flu

Influenza Virus Avian influenza Flu season Research Vaccine Treatment Genome project H5N1 strain

Image File history File links Flu_und_legende_color_c. ... Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus The Orthomyxoviridae are a family of RNA viruses which infect vertebrates. ... For the H5N1 subtype of Avian influenza see H5N1. ... Flu season is mostly a colloquial term used to describe the regular outbreak in flu cases, or even cases of the common cold during the late fall or winter. ... Flu research includes molecular virology, pathogenesis, host immune responses, genomics, and epidemiology. ... Model of Influenza Virus from NIH The flu vaccine is a vaccine to protect against the highly variable influenza virus. ... This article is about flu treatment in humans for mild human flu, which includes both efforts to reduce symptoms and treatments for the flu virus itself. ... The Influenza Genome Sequencing Project is funded by the National Institute of Allergy and Infectious Diseases (NIAID) which is a component of the National Institutes of Health (NIH), which is an agency of the United States Department of Health and Human Services. ... Influenza A virus subtype H5N1, also known as A(H5N1) or simply H5N1, is a subtype of the Influenza A virus which can cause illness in humans and many other animal species. ...

Etymology

The term influenza has its origins in 14th-century Italy, where the cause of the disease was ascribed to unfavourable astrological influences. Evolution in medical thought led to its modification to influenza del freddo, meaning "influence of the cold." The word "influenza" was first used in English in 1743 when it was borrowed during an outbreak of the disease in Europe.^[13] Archaic terms for influenza include epidemic catarrh, grippe (from the French.), sweating sickness, and Spanish fever (particularly for the 1918 pandemic strain).^[14] Hand-coloured version of the anonymous Flammarion woodcut (1888). ... The English language is a West Germanic language that originates in England. ... The 1918 flu pandemic (commonly referred to as the Spanish flu) was a category 5 influenza pandemic caused by an unusually severe and deadly Influenza A virus strain of subtype H1N1. ...

History

Further information: Influenza pandemic, Spanish flu

The influenza viruses that caused Hong Kong Flu. (magnified approximately 100,000 times)

The difference between the influenza mortality age-distributions of the 1918 epidemic and normal epidemics. Deaths per 100,000 persons in each age group, United States, for the interpandemic years 1911–1917 (dashed line) and the pandemic year 1918 (solid line).^[15]

The symptoms of human influenza were clearly described by Hippocrates roughly 2,400 years ago.^[16][17] Since then, the virus has caused numerous pandemics. Historical data on influenza are difficult to interpret, because the symptoms can be similar to those of other diseases, such as diphtheria, pneumonic plague, typhoid fever, dengue, or typhus. The first convincing record of an influenza pandemic was of an outbreak in 1580, which began in Asia and spread to Europe via Africa. In Rome over 8,000 people were killed, and several Spanish cities were almost wiped out. Pandemics continued sporadically throughout the 17th and 18th centuries, with the pandemic of 1830–1833 being particularly widespread; it infected approximately a quarter of the people exposed.^[18] An influenza pandemic is a large scale epidemic of the influenza virus, such as the 1918 Spanish flu. ... The 1918 flu pandemic (commonly referred to as the Spanish flu) was a category 5 influenza pandemic caused by an unusually severe and deadly Influenza A virus strain of subtype H1N1. ... Influenza Virus photo from http://www. ... Influenza Virus photo from http://www. ... The Hong Kong Flu was a pandemic outbreak of influenza that began in Hong Kong in 1968 and spread to the United States of America that year. ... Image File history File links W_curve. ... Image File history File links W_curve. ... For other uses, see Hippocrates (disambiguation). ... Plague redirects here. ... For a similar disease with a similar name, see typhus. ... For music group see Dengue Fever (rock band) Dengue and dengue hemorrhagic fever (DHF) are acute febrile diseases, found in the tropics, with a geographical spread similar to malaria. ... For the unrelated disease caused by Salmonella typhi, see Typhoid fever. ... For other uses, see History of Rome (disambiguation). ...

The most famous and lethal outbreak was the so-called Spanish flu pandemic (type A influenza, H1N1 subtype), which lasted from 1918 to 1919. Older estimates say it killed 40–50 million people^[19] while current estimates say 50 million to 100 million people worldwide were killed.^[20] This pandemic has been described as "the greatest medical holocaust in history" and may have killed as many people as the Black Death.^[18] This huge death toll was caused by an extremely high infection rate of up to 50% and the extreme severity of the symptoms, suspected to be caused by cytokine storms.^[19] Indeed, symptoms in 1918 were so unusual that initially influenza was misdiagnosed as dengue, cholera, or typhoid. One observer wrote, "One of the most striking of the complications was hemorrhage from mucous membranes, especially from the nose, stomach, and intestine. Bleeding from the ears and petechial hemorrhages in the skin also occurred."^[20] The majority of deaths were from bacterial pneumonia, a secondary infection caused by influenza, but the virus also killed people directly, causing massive hemorrhages and edema in the lung.^[15] The 1918 flu pandemic (commonly referred to as the Spanish flu) was a category 5 influenza pandemic caused by an unusually severe and deadly Influenza A virus strain of subtype H1N1. ... Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. ... H1N1 is a subtype of the species Influenza A virus (sometimes called bird flu virus). ... This article concerns the mid fourteenth century pandemic. ... A cytokine storm is a potentially fatal immune reaction consisting of a positive feedback loop between cytokines and immune cells. ... Cholera (or Asiatic cholera or epidemic cholera) is an extreme diarrheal disease caused by the bacterium Vibrio cholerae. ... minor Petechia A petechia (IPA pronunciation: ), plural petechiae (IPA pronunciation: ) is a small red or purple spot on the body, caused by a minor hemorrhage (broken capillary blood vessels). ... Bacterial pneumonia is an infection of the lungs by bacteria. ... A secondary infection is an infection by a microorganism subsequent to and simultaneous with an infection by a different microorganism. ... For other uses, see Bleeding (disambiguation). ... This page is about the condition called edema. ...

The Spanish flu pandemic was truly global, spreading even to the Arctic and remote Pacific islands. The unusually severe disease killed between 2 and 20% of those infected, as opposed to the more usual flu epidemic mortality rate of 0.1%.^[15][20] Another unusual feature of this pandemic was that it mostly killed young adults, with 99% of pandemic influenza deaths occurring in people under 65, and more than half in young adults 20 to 40 years old.^[21] This is unusual since influenza is normally most deadly to the very young (under age 2) and the very old (over age 70). The total mortality of the 1918–1919 pandemic is not known, but it is estimated that 2.5% to 5% of the world's population was killed. As many as 25 million may have been killed in the first 25 weeks; in contrast, HIV/AIDS has killed 25 million in its first 25 years.^[20] The red line indicates the 10°C isotherm in July, sometimes used to define the Arctic region border Artificially coloured topographical map of the Arctic region For the ship, see SS Arctic. ... Crude death rate by country Mortality rate is a measure of the number of deaths (in general, or due to a specific cause) in some population, scaled to the size of that population, per unit time. ... For other uses, see AIDS (disambiguation). ...

Later flu pandemics were not so devastating. They included the 1957 Asian Flu (type A, H2N2 strain) and the 1968 Hong Kong Flu (type A, H3N2 strain), but even these smaller outbreaks killed millions of people. In later pandemics antibiotics were available to control secondary infections and this may have helped reduce mortality compared to the Spanish Flu of 1918.^[15] The Avian Flu was a pandemic outbreak of influenza that originated in China in 1957 and spread worldwide that same year. ... The Asian Flu was a pandemic outbreak of influenza that originated in China in 1957 and spread worldwide that same year. ... The Hong Kong Flu was a pandemic outbreak of influenza that began in Hong Kong in 1968 and spread to the United States of America that year. ... H3N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus). ... Staphylococcus aureus - Antibiotics test plate. ...

The etiological cause of influenza, the Orthomyxoviridae family of viruses, was first discovered in pigs by Richard Schope in 1931.^[23] This discovery was shortly followed by the isolation of the virus from humans by a group headed by Patrick Laidlaw at the Medical Research Council of the United Kingdom in 1933.^[24] However, it was not until Wendell Stanley first crystallized tobacco mosaic virus in 1935 that the non-cellular nature of viruses was appreciated. An influenza pandemic is a large scale epidemic of the influenza virus, such as the 1918 Spanish flu. ... The Pandemic Severity Index (PSI) is a scale or index created in January 2007 by the United States Centers for Disease Control and Prevention (CDC) designed to mimic the system for indexing the severity of hurricanes (which is the Saffir-Simpson Hurricane Scale for tropical cyclones). ... The Asian Flu was a pandemic outbreak of influenza that originated in China in 1957 and spread worldwide that same year. ... The 1918 flu pandemic (commonly referred to as the Spanish flu) was a category 5 influenza pandemic caused by an unusually severe and deadly Influenza A virus strain of subtype H1N1. ... H1N1 is a subtype of the species Influenza A virus (sometimes called bird flu virus). ... The Asian Flu was a pandemic outbreak of influenza that originated in China in 1957 and spread worldwide that same year. ... The Asian Flu was a pandemic outbreak of influenza that originated in China in 1957 and spread worldwide that same year. ... H3N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus). ... H3N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus). ... This article is about the medical term. ... For other uses, see Pig (disambiguation). ... Richard Schope was the discoverer of the Orthomyxoviridae family of viruses. ... Patrick Laidlaw was one of the scientists working at the Medical Research Council at Mill hill who first isolated influenza virus from humans. ... Current MRC logo The Medical Research Council (MRC) is a UK organisation dedicated to promot[ing] the balanced development of medical and related biological research in the UK. // The MRC is one of seven Research Councils and is answerable to, although politically independent from, the Office of Science and Innovation... Wendell Meredith Stanley (August 16, 1904 - June 15, 1971) was an American biochemist, virologist and Nobel prize laureate. ... This article does not cite any references or sources. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the...

The first significant step towards preventing influenza was the development in 1944 of a killed-virus vaccine for influenza by Thomas Francis, Jr.. This built on work by Frank Macfarlane Burnet, who showed that the virus lost virulence when it was cultured in fertilized hen's eggs.^[25] Application of this observation by Francis allowed his group of researchers at the University of Michigan to develop the first influenza vaccine, with support from the U.S. Army.^[26] The Army was deeply involved in this research due to its experience of influenza in World War I, when thousands of troops were killed by the virus in a matter of months.^[20] Dr. Thomas Francis, Jr. ... Sir Frank Macfarlane Burnet OM, AK, KBE (3 September 1899 – 31 August 1985), usually known as Macfarlane or Mac Burnet, was an Australian virologist best known for his contributions to immunology. ... The University of Michigan, Ann Arbor (U of M, UM, U-M or simply Michigan) is a coeducational public research university in the state of Michigan. ... Model of Influenza Virus from NIH The flu vaccine is a vaccine to protect against the highly variable influenza virus. ... The United States Army is the largest and oldest branch of the armed forces of the United States. ... “The Great War ” redirects here. ...

Although there were scares in New Jersey in 1976 (with the Swine Flu), world wide in 1977 (with the Russian Flu), and in Hong Kong and other Asian countries in 1997 (with H5N1 avian influenza), there have been no major pandemics since the 1968 Hong Kong Flu. Immunity to previous pandemic influenza strains and vaccination may have limited the spread of the virus and may have helped prevent further pandemics.^[22] This article is about the U.S. state. ... Swine Flu is a form of Type A influenza that is normally virulent only in pigs. ... Influenza A virus subtype H5N1, also known as A(H5N1) or simply H5N1, is a subtype of the Influenza A virus which can cause illness in humans and many other animal species. ...

Microbiology

Types of influenza virus

Structure of the influenza virion. The hemagglutinin (HA) and neuraminidase (NA) proteins are shown on the surface of the particle. The viral RNAs that make up the genome are shown as red coils inside the particle and bound to Ribonuclear Proteins (RNPs).

Diagram of influenza virus nomenclature (for a Fujian flu virus)

The influenza virus is an RNA virus of the family Orthomyxoviridae, which comprises 5 genera: influenzavirus A, influenzavirus B, influenzavirus C, Isavirus, and Thogotovirus.^[27] There are three types of influenza virus: Influenzavirus A, Influenzavirus B, and Influenzavirus C. Influenza A and C infect multiple species, while influenza B almost exclusively infects humans.^[28] Wild aquatic birds are the natural hosts for a large variety of influenza A viruses. Occasionally viruses are transmitted to other species and may then cause devastating outbreaks in domestic poultry or give rise to human influenza pandemics.^[29] The type A viruses are the most virulent human pathogens among the three influenza types and cause the most severe disease. The Influenza A virus can be subdivided into different serotypes based on the antibody response to these viruses.^[28] The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are: For other uses, see Genus (disambiguation). ... Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. ... Influenzavirus B is a genus in the virus family Orthomyxoviridae. ... Influenzavirus C is a genus in the virus family Orthomyxoviridae. ... For other uses, see Species (disambiguation). ... Influenza A virus, the virus that causes Avian flu. ... Influenzavirus B is a genus in the virus family Orthomyxoviridae. ... Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus Influenzavirus C is a genus in the virus family Orthomyxoviridae, which includes those viruses which cause influenza. ... Image File history File links 3D_Influenza_virus. ... Image File history File links 3D_Influenza_virus. ... Hemagglutinin, as depicted in a simplified molecular model. ... Neuraminidase is a glycoside hydrolase enzyme (EC 3. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... The International Committee on Taxonomy of Viruses (ICTV) is a committee which authorizes and organizes the taxonomic classification of viruses. ... See H5N1 flu and Flu for details about the illnesses and H5N1 and H3N2 for details about the causitive agents. ... An RNA virus is a virus that either uses RNA as its genetic material, or whose genetic material passes through an RNA intermediate during replication. ... Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus The Orthomyxoviridae are a family of RNA viruses which infect vertebrates. ... Infectious salmon anemia or anaemia (ISA) is a viral disease of Atlantic Salmon (Salmo salar) which affect fish farms in Canada, Norway and Scotland, causing severe losses to infected farms. ... Thogotovirus is a genus in the virus family Orthomyxoviridae. ... Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. ... Influenzavirus B is a genus in the virus family Orthomyxoviridae. ... Influenzavirus C is a genus in the virus family Orthomyxoviridae. ... For other uses, see Pandemic (disambiguation). ... A serovar or serotype is a grouping of microorganisms or viruses based on their cell surface antigens. ... Each antibody binds to a specific antigen; an interaction similar to a lock and key. ...

• H1N1 caused "Spanish Flu."
• H2N2 caused "Asian Flu."
• H3N2 caused "Hong Kong Flu."
• H5N1 is a pandemic threat in 2007–8 flu season.
• H7N7 has unusual zoonotic potential.^[30]
• H1N2 is endemic in humans and pigs.
• H9N2, H7N2, H7N3, H10N7.

Influenza B virus is almost exclusively a human pathogen and is less common than influenza A. The only other animal known to be susceptible to influenza B infection is the seal.^[31] This type of influenza mutates at a rate 2–3 times lower than type A^[32] and consequently is less genetically diverse, with only one influenza B serotype.^[28] As a result of this lack of antigenic diversity, a degree of immunity to influenza B is usually acquired at an early age. However, influenza B mutates enough that lasting immunity is not possible.^[33] This reduced rate of antigenic change, combined with its limited host range (inhibiting cross species antigenic shift), ensures that pandemics of influenza B do not occur.^[34] H1N1 is a subtype of the species Influenza A virus (sometimes called bird flu virus). ... The 1918 flu pandemic (commonly referred to as the Spanish flu) was a category 5 influenza pandemic caused by an unusually severe and deadly Influenza A virus strain of subtype H1N1. ... The Asian Flu was a pandemic outbreak of influenza that originated in China in 1957 and spread worldwide that same year. ... H3N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus). ... Influenza A virus subtype H5N1, also known as A(H5N1) or simply H5N1, is a subtype of the Influenza A virus which can cause illness in humans and many other animal species. ... For other uses, see Pandemic (disambiguation). ... H7N7 is a subtype of the species avian influenza virus (bird flu virus). ... Zoonosis is any infectious disease that can be transmitted from animals, both wild and domestic, to humans. ... H1N2 is a subtype of the species avian influenza virus (bird flu virus) currently endemic in both human and pig populations. ... H9N2 is a subtype of the species avian influenza virus (bird flu virus). ... H7N2 is a subtype of the species avian influenza virus (bird flu virus). ... H7N3 is a subtype of the species avian influenza virus (bird flu virus). ... H10N7 is a subtype of the species avian influenza virus (bird flu virus). ... Families Odobenidae Otariidae Phocidae Pinnipeds (fin-feet, lit. ... An antigen or immunogen is a molecule that stimulates an immune response. ... Immunity is a medical term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. ... Antigenic shift is the process by which two different strains of influenza combine to form a new subtype having a mixture of the surface antigens of the two original strains. ...

The influenza C virus infects humans and pigs, and can cause severe illness and local epidemics.^[35] However, influenza C is less common than the other types and usually seems to cause mild disease in children.^[36][37]

Structure and properties

The following applies for Influenza A viruses, although other strains are very similar in structure:^[38] Genera Influenzavirus A Influenzavirus B Influenzavirus C Isavirus Thogotovirus Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. ...

The influenza A virus particle or virion is 80–120 nm in diameter and usually roughly spherical, although filamentous forms can occur.^[39] Unusually for a virus, the influenza A genome is not a single piece of nucleic acid; instead, it contains eight pieces of segmented negative-sense RNA (13.5 kilobases total), which encode 11 proteins (HA (hemagglutinin), NA (neuraminidase), NP (nucleoprotein), M1, M2, NS1, NS2(NEP), PA, PB1, PB1-F2, PB2).^[40] The best-characterised of these viral proteins are hemagglutinin and neuraminidase, two large glycoproteins found on the outside of the viral particles. Neuraminidase is an enzyme involved in the release of progeny virus from infected cells, by cleaving sugars that bind the mature viral particles. By contrast, hemagglutinin is a lectin that mediates binding of the virus to target cells and entry of the viral genome into the target cell.^[41] The hemagglutinin (HA or H) and neuraminidase (NA or N) proteins are targets for antiviral drugs.^[42] These proteins are also recognised by antibodies, i.e. they are antigens.^[22] The responses of antibodies to these proteins are used to classify the different serotypes of influenza A viruses, hence the H and N in H5N1. This article is about the unit of length. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... Look up nucleic acid in Wiktionary, the free dictionary. ... Sense, when applied in a molecular biology context, is a general concept used to compare the polarity of nucleic acid molecules, particularly RNA, to other nucleic acid molecules. ... For other uses, see RNA (disambiguation). ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... Hemagglutinin, as depicted in a simplified molecular model. ... Neuraminidase is a glycoside hydrolase enzyme (EC 3. ... N-linked protein glycosylation (N-glycosylation of N-glycans) at Asn residues (Asn-x-Ser/Thr motifs) in glycoproteins[1]. Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to their polypeptide backbones. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Lectins are a type of receptor proteins of non-immune origin that specifically interact with sugar molecules (carbohydrates) without modifying them. ... Antiviral drugs are a class of medication used specifically for treating viral infections. ... Each antibody binds to a specific antigen; an interaction similar to a lock and key. ... An antigen or immunogen is a molecule that stimulates an immune response. ... A serovar or serotype is a grouping of microorganisms or viruses based on their cell surface antigens. ...

Infection and replication

Host cell invasion and replication by the influenza virus. The steps in this process are discussed in the text.

Influenza viruses bind through hemagglutinin onto sialic acid sugars on the surfaces of epithelial cells; typically in the nose, throat and lungs of mammals and intestines of birds (Stage 1 in infection figure).^[43] The cell imports the virus by endocytosis. In the acidic endosome, part of the haemagglutinin protein fuses the viral envelope with the vacuole's membrane, releasing the viral RNA (vRNA) molecules, accessory proteins and RNA-dependent RNA transcriptase into the cytoplasm (Stage 2).^[44] These proteins and vRNA form a complex that is transported into the cell nucleus, where the RNA-dependent RNA transcriptase begins transcribing complementary positive-sense vRNA (Steps 3a and b).^[45] The vRNA is either exported into the cytoplasm and translated (step 4), or remains in the nucleus. Newly-synthesised viral proteins are either secreted through the Golgi apparatus onto the cell surface (in the case of neuraminidase and hemagglutinin, step 5b) or transported back into the nucleus to bind vRNA and form new viral genome particles (step 5a). Other viral proteins have multiple actions in the host cell, including degrading cellular mRNA and using the released nucleotides for vRNA synthesis and also inhibiting translation of host-cell mRNAs.^[46] Hemagglutinin, as depicted in a simplified molecular model. ... Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. ... This article is about the epithelium as it relates to animal anatomy. ... Human respiratory system The lungs flank the heart and great vessels in the chest cavity. ... In anatomy, the intestine is the segment of the alimentary canal extending from the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine. ... Endocytosis (IPA: ) is a process whereby cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane. ... In biology an endosome is a membrane-bound compartment inside cells. ... RNA replicase is a polymerase enzyme that catalyzes the self-replication of single-stranded RNA. it is RNA dependent RNA plwhich is not haVING PRROFREEDING ACTIVITY. THIS IS ANOTHER EXTENSION IN THE CENTRADOGMA. IT IS MADE UP OF THREE SUBUNIT. Categories: | ... Schematic showing the cytoplasm, with major components of a typical animal cell. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ... The interaction of mRNA in a eukaryote cell. ... A nucleotide is a chemical compound that consists of 3 portions: a heterocyclic base, a sugar, and one or more phosphate groups. ... Translation is the second stage of protein biosynthesis (part of the overall process of gene expression). ...

Negative-sense vRNAs that form the genomes of future viruses, RNA-dependent RNA transcriptase, and other viral proteins are assembled into a virion. Hemagglutinin and neuraminidase molecules cluster into a bulge in the cell membrane. The vRNA and viral core proteins leave the nucleus and enter this membrane protrusion (step 6). The mature virus buds off from the cell in a sphere of host phospholipid membrane, acquiring hemagglutinin and neuraminidase with this membrane coat (step 7).^[47] As before, the viruses adhere to the cell through hemagglutinin; the mature viruses detach once their neuraminidase has cleaved sialic acid residues from the host cell.^[43] After the release of new influenza viruses, the host cell dies. In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... Neuraminidase is a glycoside hydrolase enzyme (EC 3. ...

Because of the absence of RNA proofreading enzymes, the RNA-dependent RNA transcriptase makes a single nucleotide insertion error roughly every 10 thousand nucleotides, which is the approximate length of the influenza vRNA. Hence, nearly every newly-manufactured influenza virus is a mutant^[48] - antigenic drift. The separation of the genome into eight separate segments of vRNA allows mixing or reassortment of vRNAs if more than one viral line has infected a single cell. The resulting rapid change in viral genetics produces antigenic shifts and allow the virus to infect new host species and quickly overcome protective immunity.^[22] This is important in the emergence of pandemics, as discussed below in the section on Epidemiology. Proofreading means reading a proof copy of a text in order to detect and correct any errors. ... Antigenic shift is the process by which two different strains of influenza combine to form a new subtype having a mixture of the surface antigens of the two original strains. ...

Symptoms and diagnosis

Influenza spreads by aerosols created by coughs or sneezes.

In humans, influenza's effects are much more severe than those of the common cold, and last longer. Recovery takes about one to two weeks. Influenza, however, can be deadly, especially for the weak, old or chronically ill.^[22] The flu can worsen chronic health problems. People with emphysema, chronic bronchitis or asthma may experience shortness of breath while they have the flu, and influenza may cause worsening of coronary heart disease or congestive heart failure.^[49] Smoking is another risk factor associated with more serious disease and increased mortality from influenza.^[50] Aerosol, is a term derived from the fact that matter floating in air is a suspension (a mixture in which solid or liquid or combined solid-liquid particles are suspended in a fluid). ... Acute viral nasopharyngitis, or acute coryza, usually known as the common cold, is a highly contagious, viral infectious disease of the upper respiratory system, primarily caused by picornaviruses or coronaviruses. ... Coronary heart disease (CHD), also called coronary artery disease (CAD), ischaemic heart disease, atherosclerotic heart disease, is the end result of the accumulation of atheromatous plaques within the walls of the arteries that supply the myocardium (the muscle of the heart) with oxygen and nutrients. ... Congestive heart failure (CHF), also called congestive cardiac failure (CCF) or just heart failure, is a condition that can result from any structural or functional cardiac disorder that impairs the ability of the heart to fill with or pump a sufficient amount of blood throughout the body. ... The cigarette is the most common method of smoking tobacco. ... A risk factor is a variable associated with an increased risk of disease or infection but risk factors are not necessarily causal. ...

Symptoms

Symptoms of influenza can start quite suddenly one to two days after infection. Usually the first symptoms are chills or a chilly sensation but fever is also common early in the infection, with body temperatures as high as 39 °C (approximately 103 °F). Many people are so ill that they are confined to bed for several days, with aches and pains throughout their bodies, which are worst in their backs and legs.^[1] Symptoms of influenza may include:

• Body aches, especially joints and throat
• Coughing and sneezing
• Extreme coldness and fever
• Fatigue
• Headache
• Irritated watering eyes
• Nasal congestion
• Reddened eyes, skin (especially face), mouth, throat and nose
• Abdominal pain (in children with Influenza B)^[51]

It can be difficult to distinguish between the common cold and influenza in the early stages of these infections,^[2] but usually the symptoms of the flu are more severe than their common-cold equivalents. Research on signs and symptoms of influenza found that the best findings for excluding the diagnosis of influenza were:^[52] For other uses, see Sneeze (disambiguation). ... An analogue medical thermometer showing the temperature of 38. ... Exhaustion redirects here. ... A headache (cephalgia in medical terminology) is a condition of pain in the head; sometimes neck or upper back pain may also be interpreted as a headache. ... Nasal congestion is the blockage of the nasal passages usually due to membranes lining the nose becoming swollen from inflamed blood vessels. ...

Notes to table: The sensitivity of a binary classification test or algorithm, such as a blood test to determine if a person has a certain disease, or an automated system to detect faulty products in a factory, is a parameter that expresses something about the tests performance. ... The sensitivity of a binary classification test or algorithm, such as a blood test to determine if a person has a certain disease, or an automated system to detect faulty products in a factory, is a parameter that expresses something about the tests performance. ... The specificity is a statistical measure of how well a binary classification test correctly identifies the negative cases, or those cases that do not meet the condition under study. ...

• Sensitivity is the proportion of people who tested positive of all the positive people tested. In this case, being positive or negative is having influenza or not, and being tested positive or negative is having the symptom or not. For instance, 86% of those with influenza had fever.
• Specificity is the proportion of people who tested negative of all the negative people tested. In this case, the ones without fever only constitute 25% of those without influenza. In other words, the majority of people with fever do not have influenza.
• All three findings, especially fever, were less sensitive in patients over 60 years of age.

Since anti-viral drugs are effective in treating influenza if given early (see treatment section, below), it can be important to identify cases early. Of the symptoms listed above, the combinations of findings below can improve diagnostic accuracy.^[53] Unfortunately, even combinations of findings are imperfect. However, Bayes Theorem can combine pretest probability with clinical findings to adequately diagnose or exclude influenza in some patients. The pretest probability has a strong seasonal variation; the current prevalence of influenza among patients in the United States receiving sentinel testing is available at the CDC.^[54] Using the CDC data, the following table shows how the likelihood of influenza varies with prevalence: The sensitivity of a binary classification test or algorithm, such as a blood test to determine if a person has a certain disease, or an automated system to detect faulty products in a factory, is a parameter that expresses something about the tests performance. ... The specificity is a statistical measure of how well a binary classification test correctly identifies the negative cases, or those cases that do not meet the condition under study. ... Bayes theorem is a result in probability theory, which gives the conditional probability distribution of a random variable A given B in terms of the conditional probability distribution of variable B given A and the marginal probability distribution of A alone. ... The Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, is recognized as the leading United States agency for protecting the public health and safety of people. ...

Two decision analysis studies^[55][56] suggest that during local outbreaks of influenza, the prevalence will be over 70%^[56] and thus patients with any of the above combinations of symptoms may be treated with neuramidase inhibitors without testing. Even in the absence of a local outbreak, treatment may be justified in the elderly during the influenza season as long as the prevalence is over 15%.^[56] Decision analysis (DA) is the discipline comprising the philosophy, theory, methodology, and professional practice necessary to address important decisions in a formal manner. ...

Most people who get influenza will recover in one to two weeks, but others will develop life-threatening complications (such as pneumonia). According to the World Health Organization: "Every winter, tens of millions of people get the flu. Most are only ill and out of work for a week, yet the elderly are at a higher risk of death from the illness. We know the world-wide death toll exceeds a few hundred thousand people a year, but even in developed countries the numbers are uncertain, because medical authorities don't usually verify who actually died of influenza and who died of a flu-like illness."^[57] Even healthy people can be affected, and serious problems from influenza can happen at any age. People over 50 years old, very young children and people of any age with chronic medical conditions, are more likely to get complications from influenza: such as pneumonia, bronchitis, sinus, and ear infections.^[58] This article is about human pneumonia. ... WHO redirects here. ... Bronchitis is an inflammation of the bronchi (medium-size airways) in the lungs. ... This article does not cite any references or sources. ... Otitis media (also known as glue ear) is an inflammation of the middle ear, usually associated with a buildup of fluid. ...

Common symptoms of the flu such as fever, headaches, and fatigue come from the huge amounts of proinflammatory cytokines and chemokines (such as interferon or tumor necrosis factor) produced from influenza-infected cells.^[2][59] In contrast to the rhinovirus that causes the common cold, influenza does cause tissue damage, so symptoms are not entirely due to the inflammatory response.^[60] Cytokines are a category of less-widely-known signalling proteins and glycoproteins that, like hormones and neurotransmitters, are used extensively in cellular communication. ... Chemokines are a family of pro-inflammatory activation-inducible cytokines, or small protein signals secreted by cells. ... Interferons (IFNs) are natural proteins produced by the cells of the immune system of most vertebrates in response to challenges by foreign agents such as viruses, bacteria, parasites and tumor cells. ... In medicine, tumor necrosis factor alpha (TNFα, cachexin or cachectin) is an important cytokine involved in systemic inflammation and the acute phase response. ... Species Human rhinovirus A (HRV-A) Human rhinovirus B (HRV-B) Rhinovirus (from the Greek rhin-, which means nose) is a genus of the Picornaviridae family of viruses. ... Acute viral nasopharyngitis, or acute coryza, usually known as the common cold, is a highly contagious, viral infectious disease of the upper respiratory system, primarily caused by picornaviruses or coronaviruses. ...

Laboratory tests

The available laboratory tests for influenza continue to improve. The United States