Influenza Classification and 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 International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify Diseases The International Statistical Classification of Diseases and Related Health Problems 10th Revision ( ICD -10) is a coding of diseases and signs symptoms abnormal findings J00-J99 - Diseases of the respiratory system (J00-J06 Acute upper respiratory infections ( Acute Nasopharyngitis ( Common cold) J00-J99 - Diseases of the respiratory system (J00-J06 Acute upper respiratory infections ( Acute Nasopharyngitis ( Common cold) The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify Diseases The following is a list of codes for International Statistical Classification of Diseases and Related Health Problems. The Diseases Database is a free Website that provides information about the relationships between medical conditions Symptoms, and Medications. MedlinePlus, with the MedlinePlus Medical Encyclopedia, is a website network containing Health information from the world's largest medical Library eMedicine is an online clinical medical knowledge base that was founded in 1996 by Scott Plantz and Richard Lavely two medical doctors Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books An infectious disease is a clinically evident Disease resulting from the presence of Pathogenic microbial agents including Pathogenic viruses Pathogenic Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands An RNA virus is a Virus that has RNA (ribonucleic acid as its Genetic material. In Biological classification, family ( Latin The Orthomyxoviridae (Derivation of name orthos is Greek for straight myxa is Greek for Mucus) are a family of RNA viruses that The name influenza comes from the Italian: influenza, meaning "influence", (Latin: influentia). Italian ( or lingua italiana) is a Romance language spoken by about 63 million people as a First language, primarily in Italy. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. In humans, common symptoms of the disease are the chills, then fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort. Rigor is a shaking occurring during a high Fever. It occurs because cytokines and Prostaglandins are released as part of an Immune Fever (also known as pyrexia, from the Greek pyretos meaning fire or a febrile response, from the Latin word Febris See also Strep throat. Pharyngitis (ˌfarɪnˈdʒʌɪtɪs is in most cases a Painful inflammation of the Pharynx, and is Myalgia means " Muscle Pain " and is a symptom of many diseases and disorders A headache ( cephalalgia in medical terminology is a condition of pain in the Head; sometimes Neck or upper back pain may also be interpreted In Medicine, a cough ( Latin: tussis) is a sudden and often repetitively occurring defence Reflex which helps to clear the large breathing passages Malaise is a feeling of general discomfort or uneasiness an "out of sorts" feeling often the first indication of an infection or other disease ^[1] In more serious cases, influenza causes pneumonia, which can be fatal, particularly in young children and the elderly. A sequela, (sɨˈkwiːlə plural sequelæ) is a Pathological condition resulting from a Disease, Injury, or other trauma. Pneumonia is an inflammatory illness of the Lung. Frequently it is described as lung Parenchyma / alveolar inflammation and abnormal 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. Acute viral nasopharyngitis or acute coryza, usually known as the common cold, is a highly contagious viral Infectious disease of the ^[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". Nausea ( Latin: Nausea, Greek:, " Sea-sickness " also called wamble) is the sensation of unease and discomfort Vomiting (also called throwing up, emesis) is the forceful expulsion of the contents of one's Stomach through the Mouth and sometimes the Gastroenteritis (also known as gastro, gastric flu, and stomach flu, although unrelated to Influenza) is Inflammation of the ^[3]

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. Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas Feces, faeces, or fæces (see spelling differences) is a waste product from an animal's digestive tract expelled through the Anus Influenza can also be transmitted by saliva, nasal secretions, faeces and blood. For the band see Saliva (band; for the village in Azerbaijan see Səliva. In vertebrates mucus is a slippery secretion produced by and covering Mucous membranes It is a viscous Colloid containing Antiseptic enzymes (such as Feces, faeces, or fæces (see spelling differences) is a waste product from an animal's digestive tract expelled through the Anus Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products 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. The Celsius Temperature scale was previously known as the centigrade scale. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 ^[4][5] Most influenza strains can be inactivated easily by disinfectants and detergents. Disinfectants are Antimicrobial agents that are applied to non-living objects to destroy Microorganisms, the process of which is known as disinfection. A detergent (as a noun is a material intended to assist Cleaning. ^[6][7][8]

Flu spreads around the world in seasonal epidemics, killing millions of people in pandemic years and hundreds of thousands in non-pandemic years. See also Influenza Flu season is the portion of the year in which there is a regular outbreak in flu cases In Epidemiology, an epidemic (from Greek epi- upon + demos people is a classification of a disease that appears as new cases in a A pandemic (from Greek παν pan all + δήμος demos people is an Epidemic of Infectious disease that spreads through 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. In biology strain is a low-level Taxonomic rank used in three related ways Often, these new strains result from the spread of an existing flu virus to humans from other animal species. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. 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. Influenza A virus subtype H5[[Neuraminidase N1]], also known as A(H5N1 or simply H5N1, is a subtype of the Influenza A virus which can cause Note For information about the content tone and sourcing of this article please see the tags at the bottom of this page Fortunately, this virus has not mutated to a form that spreads easily between people. In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism ^[9]

Vaccinations against influenza are usually given to people in developed countries with a high risk of contracting the disease^[10] and to farmed poultry. Vaccination is the administration of Antigenic material (the Vaccine) to produce immunity to a disease The term developed country, or advanced country, is used to categorize countries with developed Economies in which the tertiary and quaternary sectors ^[11] The most common human vaccine is the trivalent influenza vaccine that contains purified and inactivated material from three viral strains. A Vaccine is an Inoculation designed to increase immunity against a specific disease Typically, this vaccine includes material from two influenza A virus subtypes and one influenza B virus strain. Influenzavirus A is a Genus of the Orthomyxoviridae family of Viruses Influenzavirus A includes only one Species: Influenza A virus Influenzavirus B is a genus in the Virus family Orthomyxoviridae. ^[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. Antiviral drugs are a class of Medication used specifically for treating viral Infections Like Antibiotics for Bacteria, specific antivirals Neuraminidase inhibitors are a class of Antiviral drugs targeted at the influenza viruses whose mode of action consists of blocking the function of the viral Neuraminidase

Flu

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

Etymology

The word influenza comes from the Italian language and refers to the cause of a disease; initially, this ascribed illness to unfavorable astrological influences. The Orthomyxoviridae (Derivation of name orthos is Greek for straight myxa is Greek for Mucus) are a family of RNA viruses that For the H5N1 subtype of Avian influenza see H5N1. Avian influenza, sometimes Avian flu, and commonly Bird flu refers See also Influenza Flu season is the portion of the year in which there is a regular outbreak in flu cases Influenza research involves investigating Molecular virology, Pathogenesis, host Immune responses Genomics, and Epidemiology regarding A Vaccine is an Inoculation designed to increase immunity against a specific disease 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 The Influenza Genome Sequencing Project (IGSP is an effort to dramatically improve the availability of genomic sequences and related information about the influenza (flu viruses Influenza A virus subtype H5[[Neuraminidase N1]], also known as A(H5N1 or simply H5N1, is a subtype of the Influenza A virus which can cause Italian ( or lingua italiana) is a Romance language spoken by about 63 million people as a First language, primarily in Italy. Astrology (from Greek grc ἄστρον astron, "constellation star" and grc -λογία -logia) is a group of Systems ^[13] Changes 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 adopted, with an anglicized pronunciation, during an outbreak of the disease in Europe. English is a West Germanic language originating in England and is the First language for most people in the United Kingdom, the United States ^[14] Archaic terms for influenza include epidemic catarrh, grippe (from the French), sweating sickness, and Spanish fever (particularly for the 1918 pandemic strain). French ( français,) is a Romance language spoken around the world by 118 million people as a native language and by about 180 to 260 million people The 1918 flu pandemic (commonly referred to as the Spanish flu) was an Influenza Pandemic that spread to nearly every part of the world ^[15]

History

Further information: Influenza pandemic, Spanish flu

The influenza viruses that caused Hong Kong Flu. Note For information about the content tone and sourcing of this article please see the tags at the bottom of this page The 1918 flu pandemic (commonly referred to as the Spanish flu) was an Influenza Pandemic that spread to nearly every part of the world H3N2 is a subtype of the influenza A virus. Its name derives from the forms of the two kinds of Proteins on the surface of its coat Hemagglutinin (H and (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). ^[16]

The symptoms of human influenza were clearly described by Hippocrates roughly 2,400 years ago. Hippocrates of Cos II or Hippokrates of Kos ( ca. 460 BC – ca ^[17][18] 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. Diphtheria ( Greek διφθερα ( diphthera)—“pair of leather scrolls" is an upper respiratory tract illness characterized by sore Pneumonic plague is the most virulent and least common form of plague, caused by the bacterium Yersinia pestis. Typhoid fever, also known as enteric fever, bilious fever, Yellow Jack or commonly just typhoid, is an illness caused by the Bacterium Typhus is any of several similar diseases caused by Louse -borne bacteria 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. The History of the city of Rome spans 2800 years of the existence of a city that grew from a small Italian village in the 9th century BC into the center Spain () or the Kingdom of Spain (Reino de España is a country located mostly in southwestern Europe on the Iberian Peninsula. 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. ^[19]

The most famous and lethal outbreak was the so-called Spanish flu pandemic (type A influenza, H1N1 subtype), which lasted from 1918 to 1919. The 1918 flu pandemic (commonly referred to as the Spanish flu) was an Influenza Pandemic that spread to nearly every part of the world Influenzavirus A is a Genus of the Orthomyxoviridae family of Viruses Influenzavirus A includes only one Species: Influenza A virus H1[[Neuraminidase N1]] is a subtype of the species Influenza A virus. Older estimates say it killed 40–50 million people,^[20] while current estimates say 50 million to 100 million people worldwide were killed. ^[21] This pandemic has been described as "the greatest medical holocaust in history" and may have killed as many people as the Black Death. The Black Death, or the Black Plague, was one of the deadliest Pandemics in human history widely thought to have been caused by a bacterium named Yersinia ^[19] 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. A cytokine storm is a potentially fatal immune reaction consisting of a Positive feedback loop between Cytokines and Immune cells with highly elevated ^[20] Indeed, symptoms in 1918 were so unusual that initially influenza was misdiagnosed as dengue, cholera, or typhoid. Cholera, sometimes known as Asiatic cholera or epidemic cholera, is an infectious Gastroenteritis caused by the Bacterium 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. A petechia (pɨˈtiːkiə plural petechiae (pɨˈtiːkɪiː is a small (1-2mm red or purple spot on the body caused by a minor Hemorrhage (broken Capillary "^[21] 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. See Pneumonia for a general overview of pneumonia and its other causes An infection is the detrimental Colonization of a host Organism by a foreign Species. Bleeding, technically known as hemorrhaging / haemorrhaging (see American and British spelling differences) is the loss of Blood from Oedema (or Edema in American English formerly known as dropsy or hydropsy, is the increase of Interstitial fluid in any organ &mdash swelling ^[16]

The Spanish flu pandemic was truly global, spreading even to the Arctic and remote Pacific islands. The Arctic is the Region around the Earth 's North Pole, opposite the Antarctic region around the South Pole. The unusually severe disease killed between 2 and 20% of those infected, as opposed to the more usual flu epidemic mortality rate of 0. 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 1%. ^[16][21] 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. ^[22] 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. ^[21]

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. H2N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus H2N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus H3N2 is a subtype of the influenza A virus. Its name derives from the forms of the two kinds of Proteins on the surface of its coat Hemagglutinin (H and H3N2 is a subtype of the influenza A virus. Its name derives from the forms of the two kinds of Proteins on the surface of its coat Hemagglutinin (H and In later pandemics antibiotics were available to control secondary infections and this may have helped reduce mortality compared to the Spanish Flu of 1918. In modern usage an antibiotic is a Chemotherapeutic agent with activity against Microorganisms such as Bacteria, fungi or Protozoa ^[16]

The etiological cause of influenza, the Orthomyxoviridae family of viruses, was first discovered in pigs by Richard Schope in 1931. H3N2 is a subtype of the influenza A virus. Its name derives from the forms of the two kinds of Proteins on the surface of its coat Hemagglutinin (H and Etiology (alternatively aetiology, aitiology) is the study of causation. Pigs, also called hogs or' swine', are Ungulates which have been domesticated as sources of food leather and similar products since ancient times Richard Schope was the discoverer of the Orthomyxoviridae family of viruses ^[24] 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. Patrick Playfair Laidlaw (1881-1940 was a British virologist He was one of the scientists working at the Medical Research Council at Mill Hill who first isolated The Medical Research Council (MRC is a UK organisation dedicated to "promot the balanced development of medical and related biological research The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located ^[25] However, it was not until Wendell Stanley first crystallized tobacco mosaic virus in 1935 that the non-cellular nature of viruses was appreciated. Wendell Meredith Stanley ( August 16, 1904 &ndash June 15, 1971) was an American biochemist, virologist Tobacco mosaic virus (TMV is an RNA virus that infects Plants especially Tobacco and other members of the family Solanaceae. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called

The first significant step towards preventing influenza was the development in 1944 of a killed-virus vaccine for influenza by Thomas Francis, Jr.. Thomas Francis Jr ( July 15, 1900 – October 1, 1969) was an American Physician, Virologist, and Epidemiologist This built on work by Frank Macfarlane Burnet, who showed that the virus lost virulence when it was cultured in fertilized hen's eggs. Sir Frank Macfarlane Burnet, OM, AK, KBE (3 September 1899 – 31 August 1985 usually known as Macfarlane or Mac Burnet, was ^[26] 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. The University of Michigan Ann Arbor ( U of M, U-M, UM or simply Michigan) is a top-ranked Coeducational public research A Vaccine is an Inoculation designed to increase immunity against a specific disease The United States Army is a military organization whose primary mission is to "provide necessary forces and capabilities. ^[27] 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. World War I (abbreviated WWI; also known as the First World War, the Great War, and the War to End All ^[21]

Although there were scares in New Jersey in 1976 (with the Swine Flu), worldwide 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. New Jersey ( is a state in the Mid-Atlantic and Northeastern regions of the United States. Swine Flu (or Swine influenzavirus (SIV flu) refers to a subset of Orthomyxoviridae that creates Influenza in Pigs and are endemic Hong Kong ( officially the Hong Kong Special Administrative Region, is a territory located on China 's south coast on the Pearl River Delta, and borders Influenza A virus subtype H5[[Neuraminidase N1]], also known as A(H5N1 or simply H5N1, is a subtype of the Influenza A virus which can cause Immunity to previous pandemic influenza strains and vaccination may have limited the spread of the virus and may have helped prevent further pandemics. ^[23]

Microbiology

Types of influenza virus

Structure of the influenza virion. A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic Influenzavirus A is a Genus of the Orthomyxoviridae family of Viruses Influenzavirus A includes only one Species: Influenza A virus Influenzavirus B is a genus in the Virus family Orthomyxoviridae. Influenzavirus C is a genus in the Virus family Orthomyxoviridae, which includes those Viruses which cause Influenza. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Influenzavirus A is a Genus of the Orthomyxoviridae family of Viruses Influenzavirus A includes only one Species: Influenza A virus Influenzavirus B is a genus in the Virus family Orthomyxoviridae. Influenzavirus C is a genus in the Virus family Orthomyxoviridae, which includes those Viruses which cause Influenza. The hemagglutinin (HA) and neuraminidase (NA) proteins are shown on the surface of the particle. Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses Sialidase 1 (lysosomal sialidase, also known as NEU1 or neuraminidase, is a human Gene. The viral RNAs that make up the genome are shown as red coils inside the particle and bound to Ribonuclear Proteins (RNPs). In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby

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

The influenza virus is an RNA virus of the family Orthomyxoviridae, which comprises five genera: influenzavirus A, influenzavirus B, influenzavirus C, Isavirus, and Thogotovirus. The International Committee on Taxonomy of Viruses ( ICTV) is a committee which authorizes and organizes the taxonomic classification of Viruses They have See H5N1 flu and Flu for details about the illnesses and H5N1 and H3N2 for details about the causative agents An RNA virus is a Virus that has RNA (ribonucleic acid as its Genetic material. The Orthomyxoviridae (Derivation of name orthos is Greek for straight myxa is Greek for Mucus) are a family of RNA viruses that Infectious salmon anemia or anaemia ( ISA) is a viral Disease of Atlantic Salmon ( Salmo salar) that affects fish farms Thogotovirus is a genus in the Virus family Orthomyxoviridae. ^[28] There are three types of influenza virus: Influenzavirus A, Influenzavirus B, and Influenzavirus C. Influenzavirus A is a Genus of the Orthomyxoviridae family of Viruses Influenzavirus A includes only one Species: Influenza A virus Influenzavirus B is a genus in the Virus family Orthomyxoviridae. Influenzavirus C is a genus in the Virus family Orthomyxoviridae, which includes those Viruses which cause Influenza. Influenza A and C infect multiple species, while influenza B almost exclusively infects humans. ^[29] 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. A pandemic (from Greek παν pan all + δήμος demos people is an Epidemic of Infectious disease that spreads through ^[30] 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. A serovar or serotype is a group of Microorganisms or Viruses based on their cell surface Antigens Serovars allow the epidemiologic classification Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily ^[29] The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are:

• H1N1 caused Spanish Flu. H1[[Neuraminidase N1]] is a subtype of the species Influenza A virus. The 1918 flu pandemic (commonly referred to as the Spanish flu) was an Influenza Pandemic that spread to nearly every part of the world
• H2N2 caused Asian Flu. H2N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus
• H3N2 caused Hong Kong Flu. H3N2 is a subtype of the influenza A virus. Its name derives from the forms of the two kinds of Proteins on the surface of its coat Hemagglutinin (H and
• H5N1 is a pandemic threat in the 2007–08 flu season. Influenza A virus subtype H5[[Neuraminidase N1]], also known as A(H5N1 or simply H5N1, is a subtype of the Influenza A virus which can cause A pandemic (from Greek παν pan all + δήμος demos people is an Epidemic of Infectious disease that spreads through
• H7N7 has unusual zoonotic potential. H7N7 is a subtype of the species Influenza A virus (sometimes called bird flu virus A zoonosis (ˌzoʊəˈnoʊsɨs or zoonose is any Infectious disease that is able to be transmitted (by a vector) from other Animals both wild and domestic ^[31]
• H1N2 is endemic in humans and pigs. H1[[Neuraminidase N2]] is a subtype of the species Influenza A virus (sometimes called bird flu virus
• H9N2, H7N2, H7N3, H10N7. H9N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus H7N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus H7N3 is a subtype of the species Influenza A virus (sometimes called bird flu virus H10N7 is a subtype of the species Influenza A virus (sometimes called bird flu virus

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. Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising ^[32] This type of influenza mutates at a rate 2–3 times lower than type A^[33] and consequently is less genetically diverse, with only one influenza B serotype. ^[29] As a result of this lack of antigenic diversity, a degree of immunity to influenza B is usually acquired at an early age. An antigen (from antibody-generating) or immunogen is a substance that prompts the generation of Antibodies and can cause an immune response Immunity is a material term that describes a state of having sufficient biological defenses to avoid Infection, Disease, or other unwanted biological invasion However, influenza B mutates enough that lasting immunity is not possible. ^[34] 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. Antigenic shift is the process by which at least two different strains of a virus (or different viruses especially Influenza, combine to form a new subtype ^[35]

The influenza C virus infects humans and pigs and can cause severe illness and local epidemics. ^[36] However, influenza C is less common than the other types and usually seems to cause mild disease in children. ^[37][38]

Structure and properties

The following applies for influenza A viruses, although other strains are very similar in structure:^[39]

The influenza A virus particle or virion is 80–120 nm in diameter and usually roughly spherical, although filamentous forms can occur. Influenzavirus A is a Genus of the Orthomyxoviridae family of Viruses Influenzavirus A includes only one Species: Influenza A virus The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International ^[40] 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. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby A nucleic acid is a Macromolecule composed of chains of monomeric Nucleotides In Biochemistry these Molecules carry Genetic information Sense, when applied in a Molecular biology context is a general concept used to compare the polarity of Nucleic acid molecules such as DNA or RNA Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units 5 kilobases total), which encode 11 proteins (HA (hemagglutinin), NA (neuraminidase), NP (nucleoprotein), M1, M2, NS1, NS2(NEP), PA, PB1, PB1-F2, PB2). Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl ^[41] The best-characterised of these viral proteins are hemagglutinin and neuraminidase, two large glycoproteins found on the outside of the viral particles. Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses Sialidase 1 (lysosomal sialidase, also known as NEU1 or neuraminidase, is a human Gene. Not to be confused with Peptidoglycan. Glycoproteins are proteins that contain Oligosaccharide chains ( Glycans) covalently attached Neuraminidase is an enzyme involved in the release of progeny virus from infected cells, by cleaving sugars that bind the mature viral particles. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins 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. Lectins are sugar-binding Proteins which are highly specific for their sugar Moieties. ^[42] The hemagglutinin (HA or H) and neuraminidase (NA or N) proteins are targets for antiviral drugs. Antiviral drugs are a class of Medication used specifically for treating viral Infections Like Antibiotics for Bacteria, specific antivirals ^[43] These proteins are also recognised by antibodies, i. Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily e. they are antigens. An antigen (from antibody-generating) or immunogen is a substance that prompts the generation of Antibodies and can cause an immune response ^[23] 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. A serovar or serotype is a group of Microorganisms or Viruses based on their cell surface Antigens Serovars allow the epidemiologic classification

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). Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses Sialic acid is a generic term for the N - or O -substituted derivatives of Neuraminic acid, a Monosaccharide with a nine- Carbon backbone In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive 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 ^[44] The cell imports the virus by endocytosis. Endocytosis is a process where cells absorb material ( Molecules such as proteins from the outside by engulfing it with their Cell membrane. In the acidic endosome, part of the hemagglutinin protein fuses the viral envelope with the vacuole's membrane, releasing the viral RNA (vRNA) molecules, accessory proteins and RNA-dependent RNA polymerase into the cytoplasm (Stage 2). In Biology, an endosome is a membrane-bound compartment inside cells roughly 300-400 nm in diameter when fully mature RNA-dependent RNA polymerase ( RDRP) or RNA replicase, is an Enzyme that catalyzes the replication of RNA from an RNA template The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. ^[45] These proteins and vRNA form a complex that is transported into the cell nucleus, where the RNA-dependent RNA polymerase begins transcribing complementary positive-sense vRNA (Steps 3a and b). In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed ^[46] 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). The Golgi apparatus (also called the 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. Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) ^[47]

Negative-sense vRNAs that form the genomes of future viruses, RNA-dependent RNA polymerase, and other viral proteins are assembled into a virion. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby 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). ^[48] 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. Sialidase 1 (lysosomal sialidase, also known as NEU1 or neuraminidase, is a human Gene. ^[44] After the release of new influenza viruses, the host cell dies.

Because of the absence of RNA proofreading enzymes, the RNA-dependent RNA polymerase makes a single nucleotide insertion error roughly every 10 thousand nucleotides, which is the approximate length of the influenza vRNA. Proofreading traditionally means reading a proof copy of a text in order to detect and correct any errors Hence, nearly every newly-manufactured influenza virus is a mutant^[49]—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 allows the virus to infect new host species and quickly overcome protective immunity. Antigenic shift is the process by which at least two different strains of a virus (or different viruses especially Influenza, combine to form a new subtype ^[23] This is important in the emergence of pandemics, as discussed below in the section on Epidemiology.

Symptoms and diagnosis

Influenza spreads by aerosols created by coughs or sneezes. Technically an aerosol is a suspension of fine solid particles or liquid droplets in a gas

In humans, influenza's effects are much more severe and last longer than those of the common cold. Acute viral nasopharyngitis or acute coryza, usually known as the common cold, is a highly contagious viral Infectious disease of the Recovery takes about one to two weeks. Influenza, however, can be deadly, especially for the weak, old or chronically ill. ^[23] 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. Coronary disease (or coronary heart disease) refers to the failure of Coronary circulation to supply adequate circulation to Cardiac muscle and surrounding Heart failure is a Cardiac condition that occurs when a problem with the structure or function of the Heart impairs its ability to supply ^[50] Smoking is another risk factor associated with more serious disease and increased mortality from influenza. Tobacco Smoking is the inhalation of smoke from burned dried or cured leaves of the Tobacco plant most often in the form of a Cigarette. A risk factor is a variable associated with an increased risk of Disease or Infection. ^[51]

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 worse 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)^[52]

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. In Medicine, a cough ( Latin: tussis) is a sudden and often repetitively occurring defence Reflex which helps to clear the large breathing passages A sneeze (or sternutation) is a semi-autonomous Convulsive expulsion of Air from the Lungs, most commonly caused by foreign particles Fever (also known as pyrexia, from the Greek pyretos meaning fire or a febrile response, from the Latin word Febris A headache ( cephalalgia in medical terminology is a condition of pain in the Head; sometimes Neck or upper back pain may also be interpreted Nasal congestion is the blockage of the nasal passages usually due to membranes lining the nose becoming swollen from inflamed blood vessels Research on signs and symptoms of influenza found that the best findings for excluding the diagnosis of influenza were:^[53]

Notes to table:

• 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. ^[54] 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. In Probability theory, Bayes' theorem (often called Bayes' law after Thomas Bayes) relates the conditional and marginal probabilities of two 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. The Centers for Disease Control and Prevention (or CDC) is an agency of the United States Department of Health and Human Services based in unincorporated ^[55] Using the CDC data, the following table shows how the likelihood of influenza varies with prevalence:

Two decision analysis studies^[56][57] suggest that during local outbreaks of influenza, the prevalence will be over 70%,^[57] and thus patients with any of the above combinations of symptoms may be treated with neuramidase inhibitors without testing. Decision Analysis (DA is the Discipline comprising the Philosophy, Theory, Methodology, and Professional practice necessary to address 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%. ^[57]

Most people who get influenza will recover in one to two weeks, but others will develop life-threatening complications (such as pneumonia). Pneumonia is an inflammatory illness of the Lung. Frequently it is described as lung Parenchyma / alveolar inflammation and abnormal 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. "^[58] 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. Bronchitis is an Inflammation of the Bronchi. More specifically it may refer to Acute bronchitis, caused by viruses or bacteria and lasting Paranasal sinuses are air-filled spaces communicating with the nasal cavity within the bones of the Skull and face Otitis is a general term for inflammation or infection of the ear in both humans and other animals ^[59]

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. Cytokines are a category of signalling Proteins and Glycoproteins that like Hormones and Neurotransmitters, are used extensively in cellular Chemokines are a family of small Cytokines, or Proteins secreted by cells Proteins are classified as chemokines according to shared structural characteristics Interferons ( IFN s are natural Proteins produced by the cells of the Immune system of most Vertebrates in response to challenges by foreign agents Tumor necrosis factor ( TNF, cachexin or cachectin and formally known as Tumor necrosis factor-alpha) is a Cytokine involved in systemic ^[2][60] 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. Rhinovirus (from the Greek rhin - which means "nose" is a genus of the Picornaviridae family of Viruses Rhinoviruses Acute viral nasopharyngitis or acute coryza, usually known as the common cold, is a highly contagious viral Infectious disease of the ^[61]

Laboratory tests

The available laboratory tests for influenza continue to improve. The United States Centers for Disease Control and Prevention (CDC) maintains an up-to-date summary of available laboratory tests. The United States of America —commonly referred to as the The Centers for Disease Control and Prevention (or CDC) is an agency of the United States Department of Health and Human Services based in unincorporated ^[62] According to the CDC, rapid diagnostic tests have a sensitivity of 70–75% and specificity of 90–95% when compared with viral culture. These tests may be especially useful during the influenza season (prevalence=25%) but in the absence of a local outbreak, or peri-influenza season (prevalence=10%^[57]).

Epidemiology

Seasonal variations

Further information: Flu season

Cumulative Confirmed Human Cases of H5N1. See also Influenza Flu season is the portion of the year in which there is a regular outbreak in flu cases ^[63] The regression curve for deaths is shown extended through the end of April 2007.

Influenza reaches peak prevalence in winter, and because the Northern and Southern Hemispheres have winter at different times of the year, there are actually two different flu seasons each year. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' Southern Hemisphere is the half of a Planet that is South of the Equator —the word hemisphere literally means 'half ball' This is why the World Health Organization (assisted by the National Influenza Centers) makes recommendations for two different vaccine formulations every year; one for the Northern, and one for the Southern Hemisphere. National Influenza Centers (also called National Influenza Centres) are institutions which are formally recognized as such by the World Health Organization (WHO ^[64]

It is not completely clear why outbreaks of the flu occur seasonally rather than uniformly throughout the year. One possible explanation is that, because people are indoors more often during the winter, they are in close contact more often, and this promotes transmission from person to person. Another is that cold temperatures lead to drier air, which may dehydrate mucus, preventing the body from effectively expelling virus particles. The virus may also survive longer on exposed surfaces (doorknobs, countertops, etc. ) in colder temperatures. Increased travel due to the Northern Hemisphere winter holiday season may also play a role. ^[65] A contributing factor is that aerosol transmission of the virus is highest in cold environments (less than 5 °C) with low humidity. ^[66] However, seasonal changes in infection rates also occur in tropical regions, and these peaks of infection are seen mainly during the rainy season. ^[67] Seasonal changes in contact rates from school terms, which are a major factor in other childhood diseases such as measles and pertussis, may also play a role in the flu. Measles (rubeola is a Disease caused by a virus specifically a Paramyxovirus of the genus Morbillivirus. Pertussis, also known as whooping cough, is a highly contagious Disease caused by the Bacterium Bordetella pertussis; it derived its A combination of these small seasonal effects may be amplified by dynamical resonance with the endogenous disease cycles. ^[68] H5N1 exhibits seasonality in both humans and birds. Influenza A virus subtype H5[[Neuraminidase N1]], also known as A(H5N1 or simply H5N1, is a subtype of the Influenza A virus which can cause ^[63]

An alternative hypothesis to explain seasonality in influenza infections is an effect of vitamin D levels on immunity to the virus. Vitamin D is a group of fat-soluble Prohormones, the two major forms of which are vitamin D2 (or Ergocalciferol) and vitamin D3 (or ^[69] This idea was first proposed by Robert Edgar Hope-Simpson in 1965. Robert Edgar Hope-Simpson was a General practitioner. He showed that Shingles was caused by reactivation of the Chickenpox Virus. ^[70] He proposed that the cause of influenza epidemics during winter may be connected to seasonal fluctuations of vitamin D, which is produced in the skin under the influence of solar (or artificial) UV radiation. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays This could explain why influenza occurs mostly in winter and during the tropical rainy season, when people stay indoors, away from the sun, and their vitamin D levels fall. Furthermore, some studies have suggested that administering cod liver oil, which contains large amounts of vitamin D, can reduce the incidence of respiratory tract infections. This article is about the fish extract for the traditional Newfoundland song see " Cod Liver Oil (song " ^[71]

Epidemic and pandemic spread

Further information: Flu pandemic

Antigenic drift creates influenza viruses with slightly modified antigens, while antigenic shift generates viruses with entirely novel antigens. Note For information about the content tone and sourcing of this article please see the tags at the bottom of this page Antigenic drift is the process of random accumulation of Mutations in viral genes recognized by the Immune system. Antigenic shift is the process by which at least two different strains of a virus (or different viruses especially Influenza, combine to form a new subtype

How antigenic shift, or reassortment, can result in novel and highly pathogenic strains of human influenza

As influenza is caused by a variety of species and strains of viruses, in any given year some strains can die out while others create epidemics, while yet another strain can cause a pandemic. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable In Epidemiology, an epidemic (from Greek epi- upon + demos people is a classification of a disease that appears as new cases in a A pandemic (from Greek παν pan all + δήμος demos people is an Epidemic of Infectious disease that spreads through Typically, in a year's normal two flu seasons (one per hemisphere), there are between three and five million cases of severe illness and up to 500,000 deaths worldwide, which by some definitions is a yearly influenza epidemic. See also Influenza Flu season is the portion of the year in which there is a regular outbreak in flu cases ^[72] Although the incidence of influenza can vary widely between years, approximately 36,000 deaths and more than 200,000 hospitalizations are directly associated with influenza every year in America. ^[73][74][75] Every ten to twenty years, a pandemic occurs, which infects a large proportion of the world's population and can kill tens of millions of people (see history section).

New influenza viruses are constantly being produced by mutation or by reassortment. In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism Reassortment is the mixing of the genetic material of two similar Viruses that are infecting the same cell ^[29] Mutations can cause small changes in the hemagglutinin and neuraminidase antigens on the surface of the virus. An antigen (from antibody-generating) or immunogen is a substance that prompts the generation of Antibodies and can cause an immune response This is called antigenic drift, which creates an increasing variety of strains over time until one of the variants eventually achieves higher fitness, becomes dominant, and rapidly sweeps through the human population—often causing an epidemic. Antigenic drift is the process of random accumulation of Mutations in viral genes recognized by the Immune system. Fitness (often denoted w in Population genetics models is a central concept in evolutionary theory. ^[76] In contrast, when influenza viruses reassort, they may acquire new antigens—for example by reassortment between avian strains and human strains; this is called antigenic shift. If a human influenza virus is produced with entirely novel antigens, everybody will be susceptible, and the novel influenza will spread uncontrollably, causing a pandemic. ^[77] In contrast to this model of pandemics based on antigenic drift and shift, an alternative approach has been proposed where the periodic pandemics are produced by interactions of a fixed set of viral strains with a human population with a constantly changing set of immunities to different viral strains. ^[78]

Prevention

Vaccination and infection control

Further information: Influenza vaccine

Vaccination against influenza with an influenza vaccine is often recommended for high-risk groups, such as children and the elderly. A Vaccine is an Inoculation designed to increase immunity against a specific disease A Vaccine is an Inoculation designed to increase immunity against a specific disease Influenza vaccines can be produced in several ways; the most common method is to grow the virus in fertilized hen eggs. The chicken ( Gallus gallus, sometimes G gallus domesticus) is a domesticated Fowl which is traditionally believed to have descended from After purification, the virus is inactivated (for example, by treatment with detergent) to produce an inactivated-virus vaccine. Alternatively, the virus can be grown in eggs until it loses virulence and the avirulent virus given as a live vaccine. Virulence (also called pestiferousness) refers to the degree of Pathogenicity of a Microbe, or in other words the relative ability of a Microbe ^[23] The effectiveness of these influenza vaccines is variable. Due to the high mutation rate of the virus, a particular influenza vaccine usually confers protection for no more than a few years. Every year, the World Health Organization predicts which strains of the virus are most likely to be circulating in the next year, allowing pharmaceutical companies to develop vaccines that will provide the best immunity against these strains. ^[64] Vaccines have also been developed to protect poultry from avian influenza. Poultry is the category of Domesticated Birds which some humans keep for the purpose of collecting their eggs, or kill for their Meat and/or For the H5N1 subtype of Avian influenza see H5N1. Avian influenza, sometimes Avian flu, and commonly Bird flu refers These vaccines can be effective against multiple strains and are used either as part of a preventative strategy, or combined with culling in attempts to eradicate outbreaks. Culling is the 'selection' (removal and killing of surplus animals from an animal population ^[79]

It is possible to get vaccinated and still get influenza. The vaccine is reformulated each season for a few specific flu strains but cannot possibly include all the strains actively infecting people in the world for that season. It takes about six months for the manufacturers to formulate and produce the millions of doses required to deal with the seasonal epidemics; occasionally, a new or overlooked strain becomes prominent during that time and infects people although they have been vaccinated (as by the H3N2 Fujian flu in the 2003–2004 flu season). See H5N1 flu and Flu for details about the illnesses and H5N1 and H3N2 for details about the causative agents ^[80] It is also possible to get infected just before vaccination and get sick with the very strain that the vaccine is supposed to prevent, as the vaccine takes about two weeks to become effective. ^[59]

The 2006–2007 season was the first in which the CDC had recommended that children younger than 59 months receive the annual influenza vaccine. ^[81] Vaccines can cause the immune system to react as if the body were actually being infected, and general infection symptoms (many cold and flu symptoms are just general infection symptoms) can appear, though these symptoms are usually not as severe or long-lasting as influenza. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor The most dangerous side-effect is a severe allergic reaction to either the virus material itself or residues from the hen eggs used to grow the influenza; however, these reactions are extremely rare. Allergy is a disorder of the Immune system often also referred to as Atopy. ^[82]

U.S. Navy personnel receiving influenza vaccination

Good personal health and hygiene habits are reasonably effective in avoiding and minimizing influenza. Note For information about the content tone and sourcing of this article please see the tags at the bottom of this page People who contract influenza are most infective between the second and third days after infection and infectivity lasts for around ten days. ^[83] Children are notably more infectious than adults and shed virus from just before they develop symptoms until two weeks after infection. ^[83][84]

Since influenza spreads through aerosols and contact with contaminated surfaces, it is important to persuade people to cover their mouths while sneezing and to wash their hands regularly. Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas ^[81] Surface sanitizing is recommended in areas where influenza may be present on surfaces. ^[85] Alcohol is an effective sanitizer against influenza viruses, while quaternary ammonium compounds can be used with alcohol to increase the duration of the sanitizing action. In Chemistry, an alcohol is any Organic compound in which a Hydroxyl group ( - O[[hydrogen H]]) is bound to a Carbon Quaternary ammonium cations, also known as quats, are positively charged Polyatomic ions of the structure NR4+ with R being ^[86] In hospitals, quaternary ammonium compounds and halogen-releasing agents such as sodium hypochlorite are commonly used to sanitize rooms or equipment that have been occupied by patients with influenza symptoms. Sodium hypochlorite is a Chemical compound with the formula NaClO ^[86] During past pandemics, closing schools, churches and theaters slowed the spread of the virus but did not have a large effect on the overall death rate. ^[87][88]

Treatment

Further information: Influenza treatment

People with the flu are advised to get plenty of rest, drink a lot of liquids, avoid using alcohol and tobacco and, if necessary, take medications such as paracetamol (acetaminophen) to relieve the fever and muscle aches associated with the flu. 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 Tobacco Smoking is the inhalation of smoke from burned dried or cured leaves of the Tobacco plant most often in the form of a Cigarette. Paracetamol ( INN) (ˌpærəˈsiːtəmɒl -ˈsɛtə- or acetaminophen ( USAN) is a widely-used Analgesic and Antipyretic Medication Children and teenagers with flu symptoms (particularly fever) should avoid taking aspirin during an influenza infection (especially influenza type B), because doing so can lead to Reye's syndrome, a rare but potentially fatal disease of the liver. Aspirin, or acetylsalicylic acid (ASA (əˌsɛtɨlsælɨˌsɪlɨk ˈæsɨd is a Salicylate drug, often used as an Analgesic to relieve Influenzavirus B is a genus in the Virus family Orthomyxoviridae. Reye's syndrome is a potentially fatal Disease that causes numerous detrimental effects to many organs especially the Brain and Liver. The liver is a vital organ in the human body and is present in Vertebrates and some other animals ^[89] Since influenza is caused by a virus, antibiotics have no effect on the infection; unless prescribed for secondary infections such as bacterial pneumonia, they may lead to resistant bacteria. In modern usage an antibiotic is a Chemotherapeutic agent with activity against Microorganisms such as Bacteria, fungi or Protozoa An infection is the detrimental Colonization of a host Organism by a foreign Species. See Pneumonia for a general overview of pneumonia and its other causes Antiviral medication is sometimes effective, but viruses can develop resistance to the standard antiviral drugs.

The two classes of anti-virals are neuraminidase inhibitors and M2 inhibitors (adamantane derivatives). Adamantane (tricyclodecane is a colourless crystalline compound with a Camphor -like odour Neuraminidase inhibitors are currently preferred for flu virus infections. The CDC recommended against using M2 inhibitors during the 2005–06 influenza season. ^[90]

Neuraminidase inhibitors

Antiviral drugs such as oseltamivir (trade name Tamiflu) and zanamivir (trade name Relenza) are neuraminidase inhibitors that are designed to halt the spread of the virus in the body. Oseltamivir ( INN) (ɒsəlˈtæmɨvɪr is an Antiviral drug that is used in the treatment and Prophylaxis of both Influenzavirus A and Influenzavirus Zanamivir ( INN) (zəˈnæmɨvɪr is a Neuraminidase inhibitor used in the treatment of and Prophylaxis of both Influenzavirus A and Influenzavirus Neuraminidase inhibitors are a class of Antiviral drugs targeted at the influenza viruses whose mode of action consists of blocking the function of the viral Neuraminidase ^[91] These drugs are often effective against both influenza A and B. ^[92] The Cochrane Collaboration reviewed these drugs and concluded that they reduce symptoms and complications. The Cochrane Collaboration is a group of over 11500 volunteers in more than 90 countries who apply a rigorous systematic process to review the effects of interventions tested in biomedical ^[93] Different strains of influenza viruses have differing degrees of resistance against these antivirals, and it is impossible to predict what degree of resistance a future pandemic strain might have. ^[94]

M2 inhibitors (adamantanes)

The antiviral drugs amantadine and rimantadine are designed to block a viral ion channel (M2 protein) and prevent the virus from infecting cells. Antiviral drugs are a class of Medication used specifically for treating viral Infections Like Antibiotics for Bacteria, specific antivirals Amantadine is the Organic compound known formally as 1-aminoadamantane Rimantadine ( INN, sold under the trade name Flumadine) is an orally administered Antiviral drug used to treat and in rare cases prevent Influenzavirus Ion channels are pore-forming Proteins that help establish and control the small Voltage Gradient across the Plasma membrane of all living The M2 protein is a Proton -selective Ion channel Protein, integral in the Viral envelope of the Influenza A Virus. These drugs are sometimes effective against influenza A if given early in the infection but are always ineffective against influenza B. ^[92] Measured resistance to amantadine and rimantadine in American isolates of H3N2 has increased to 91% in 2005. H3N2 is a subtype of the influenza A virus. Its name derives from the forms of the two kinds of Proteins on the surface of its coat Hemagglutinin (H and ^[95]

Research

Further information: Influenza research

CDC scientist working on influenza under high bio-safety conditions

Research on influenza includes studies on molecular virology, how the virus produces disease (pathogenesis), host immune responses, viral genomics, and how the virus spreads (epidemiology). Influenza research involves investigating Molecular virology, Pathogenesis, host Immune responses Genomics, and Epidemiology regarding Molecular Virology is the study of viruses at the molecular level The term pathogenesis means step by step development of a disease due to a series of changes in the structure and /or function of a cell/tissue/organ being caused by a microbial, chemical or physical An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Genomics is the study of an organism's entire Genome. The field includes intensive efforts to determine the entire DNA sequence of organisms and fine-scale Genetic Epidemiology is the study of factors affecting the Health and Illness of populations and serves as the foundation and Logic of interventions made in the These studies help in developing influenza countermeasures; for example, a better understanding of the body's immune system response helps vaccine development, and a detailed picture of how influenza invades cells aids the development of antiviral drugs. A vaccine is a biological preparation which is used to establish or improve immunity to a particular disease One important basic research program is the Influenza Genome Sequencing Project, which is creating a library of influenza sequences; this library should help clarify which factors make one strain more lethal than another, which genes most affect immunogenicity, and how the virus evolves over time. The Influenza Genome Sequencing Project (IGSP is an effort to dramatically improve the availability of genomic sequences and related information about the influenza (flu viruses Immunogenicity is the ability of a particular substance which is called the Antigen, to provoke an Immune response. eVolution is the third Album by eLDee, it was due to be released in 2008 ^[96]

Research into new vaccines is particularly important, as current vaccines are very slow and expensive to produce and must be reformulated every year. The sequencing of the influenza genome and recombinant DNA technology may accelerate the generation of new vaccine strains by allowing scientists to substitute new antigens into a previously developed vaccine strain. Recombinant DNA is a form of synthetic DNA that is engineered through the combination or insertion of one or more DNA strands thereby combining DNA sequences ^[97] New technologies are also being developed to grow viruses in cell culture, which promises higher yields, less cost, better quality and surge capacity. Cell culture is the process by which prokaryotic, or eukaryotic cells are grown under controlled conditions ^[98] Research on a universal influenza A vaccine, targeted against the external domain of the transmembrane viral M2 protein (M2e), is being done at the University of Ghent by Walter Fiers, Xavier Saelens and their team^{[99][100][101]} and has now successfully concluded Phase I clinical trials. The M2 protein is a Proton -selective Ion channel Protein, integral in the Viral envelope of the Influenza A Virus. Ghent University (in Dutch Universiteit Gent, abbreviated UGent) is one of the three large Flemish universities. Walter Fiers (b Ieper, Belgium, 1931 is a Belgian molecular biologist Xavier Saelens (b 1965 is a Belgian scientist and currently his main research interest is finding a universal Influenza Vaccine.

The US government has purchased from Sanofi Pasteur and Chiron Corporation several million doses of vaccine meant to be used in case of an influenza pandemic of H5N1 avian influenza and is conducting clinical trials with these vaccines. Sanofi pasteur Chiron Corporation was a Multinational biotechnology firm based in Emeryville California that was acquired by Novartis International AG on April 20 Note For information about the content tone and sourcing of this article please see the tags at the bottom of this page Influenza A virus subtype H5[[Neuraminidase N1]], also known as A(H5N1 or simply H5N1, is a subtype of the Influenza A virus which can cause ^[102] The UK government is also stockpiling millions of doses of antiviral drugs (oseltamivir (Tamiflu), zanimivir (Relanza)) to give to its citizens in the event of an outbreak; the UK Health Protection Agency has also gathered a limited amount of HPAI H5N1 vaccines for experimental purposes. The Health Protection Agency ( HPA) originally established as a special health authority (SpHA in 2003, is an Non-Departmental Public Body charged

Infection in other animals

H5N1

Influenza A virus subtype H5N1 Genetic structure Infection Human mortality Global spread in 2004, 2005, 2006, 2007 Social impact Pandemic

Further information: Influenzavirus A, H5N1 and Transmission and infection of H5N1

Influenza infects many animal species, and transfer of viral strains between species can occur. Influenzavirus A is a Genus of the Orthomyxoviridae family of Viruses Influenzavirus A includes only one Species: Influenza A virus Influenza A virus subtype H5[[Neuraminidase N1]], also known as A(H5N1 or simply H5N1, is a subtype of the Influenza A virus which can cause H5N1 genetic structure is the molecular structure of the H5N1 virus's RNA. Transmission and infection of H5N1 from infected avian sources to humans is a concern due to the Global spread of H5N1 that constitutes a Pandemic threat Human mortality from H5N1 or the human fatality ratio from H5N1 or the case-fatality rate of H5N1 refer to the ratio of Human and bird cases 1959-1997 A highly pathogenic strain of H5N1 caused Flu outbreaks with significant spread to numerous farms See also Global spread of H5N1, The global spread of (highly pathogenic H5N1 in Birds is considered a significant pandemic threat See also Global spread of H5N1, The global spread of (highly pathogenic H5N1 in Birds is considered a significant pandemic threat See also Global spread of H5N1, The global spread of (highly pathogenic H5N1 in birds is considered a significant pandemic threat See also Global spread of H5N1, The global spread of (highly pathogenic H5N1 in Birds is considered a significant pandemic threat Financial According to the New York Times, due to the H5N1 threat as of March 2006 "governments worldwide have spent billions planning Note For information about the content tone and sourcing of this article please see the tags at the bottom of this page Influenzavirus A is a Genus of the Orthomyxoviridae family of Viruses Influenzavirus A includes only one Species: Influenza A virus Influenza A virus subtype H5[[Neuraminidase N1]], also known as A(H5N1 or simply H5N1, is a subtype of the Influenza A virus which can cause Transmission and infection of H5N1 from infected avian sources to humans is a concern due to the Global spread of H5N1 that constitutes a Pandemic threat Birds are thought to be the main animal reservoirs of influenza viruses. Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. In Biology, a host is an organism that harbors a Virus or Parasite, or a mutual or Commensal Symbiont, typically providing nourishment ^[103] Sixteen forms of hemagglutinin and nine forms of neuraminidase have been identified. Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses Sialidase 1 (lysosomal sialidase, also known as NEU1 or neuraminidase, is a human Gene. All known subtypes (HxNy) are found in birds, but many subtypes are endemic in humans, dogs, horses, and pigs; populations of camels, ferrets, cats, seals, mink, and whales also show evidence of prior infection or exposure to influenza. The dog ( Canis lupus familiaris) is a domesticated Subspecies of the gray wolf, a Mammal of the Canidae family of the order The horse ( Equus caballus) is a hoofed ( Ungulate) Mammal, one of eight living species of the family Equidae. Pigs, also called hogs or' swine', are Ungulates which have been domesticated as sources of food leather and similar products since ancient times Camels are Even-toed ungulates within the Genus Camelus. The Dromedary, one-humped or Arabian camel has a single hump and the The ferret is a domestic Mammal of the type Mustela putorius furo. WikipediaManual of Style (spelling, articles should conform to one overall spelling style of English typically the one most linked to the article topic (if it is geographic Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising There are two living species of " mink," the American Mink and the European Mink. Whales are marine mammals which are neither Dolphins (ie members of the families Delphinidae or Platanistoidae) nor Porpoises Orcas ^[34] Variants of flu virus are sometimes named according to the species the strain is endemic in or adapted to. The main variants named using this convention are: Bird Flu, Human Flu, Swine Flu, Horse Flu and Dog Flu. For the H5N1 subtype of Avian influenza see H5N1. Avian influenza, sometimes Avian flu, and commonly Bird flu refers See also Influenza Human flu refers to a subset of Orthomyxoviridae that create Influenza in Humans and are endemic in humans Swine Flu (or Swine influenzavirus (SIV flu) refers to a subset of Orthomyxoviridae that creates Influenza in Pigs and are endemic Equine influenza ( Horse flu) refers to varieties of Influenzavirus A that are endemic in Horses Horse flu viruses were first isolated in 1956 Canine influenza or dog flu refers to varieties of Influenzavirus A that create Influenza in canines. (Cat flu generally refers to Feline viral rhinotracheitis or Feline calicivirus and not infection from an influenza virus. Cat flu is feline upper Respiratory tract disease It is generally a Misnomer since it usually does not refer to an infection by an Influenza Feline viral rhinotracheitis (FVR is an upper respiratory infection of Cats caused by feline herpesvirus 1, of the family Herpesviridae. Feline calicivirus (FCV is a Virus of the family Caliciviridae that causes disease in Cats It is one of the two important viral ) In pigs, horses and dogs, influenza symptoms are similar to humans, with cough, fever and loss of appetite. ^[34] The frequency of animal diseases are not as well-studied as human infection, but an outbreak of influenza in harbour seals caused approximately 500 seal deaths off the New England coast in 1979–1980. History See also History of New England New England's earliest inhabitants were Algonquian -speaking Native Americans including the ^[104] On the other hand, outbreaks in pigs are common and do not cause severe mortality. ^[34]

Flu symptoms in birds are variable and can be unspecific. ^[105] The symptoms following infection with low-pathogenicity avian influenza may be as mild as ruffled feathers, a small reduction in egg production, or weight loss combined with minor respiratory disease. ^[106] Since these mild symptoms can make diagnosis in the field difficult, tracking the spread of avian influenza requires laboratory testing of samples from infected birds. For the H5N1 subtype of Avian influenza see H5N1. Avian influenza, sometimes Avian flu, and commonly Bird flu refers Some strains such as Asian H9N2 are highly virulent to poultry and may cause more extreme symptoms and significant mortality. H9N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus ^[107] In its most highly pathogenic form, influenza in chickens and turkeys produces a sudden appearance of severe symptoms and almost 100% mortality within two days. The chicken ( Gallus gallus, sometimes G gallus domesticus) is a domesticated Fowl which is traditionally believed to have descended from A turkey is either of two extant Species of large Birds in the Genus Meleagris native to North America. ^[108] As the virus spreads rapidly in the crowded conditions seen in the intensive farming of chickens and turkeys, these outbreaks can cause large economic losses to poultry farmers. Intensive farming or intensive agriculture is an Agricultural production system characterized by the high Inputs of Capital, Fertilizers

An avian-adapted, highly pathogenic strain of H5N1 (called HPAI A(H5N1), for "highly pathogenic avian influenza virus of type A of subtype H5N1") causes H5N1 flu, commonly known as "avian influenza" or simply "bird flu", and is endemic in many bird populations, especially in Southeast Asia. Transmission and infection of H5N1 from infected avian sources to humans is a concern due to the Global spread of H5N1 that constitutes a Pandemic threat In Epidemiology, an Infection is said to be endemic (from Greek en- in or within + demos people in a Population when This Asian lineage strain of HPAI A(H5N1) is spreading globally. Human and bird cases 1959-1997 A highly pathogenic strain of H5N1 caused Flu outbreaks with significant spread to numerous farms It is epizootic (an epidemic in non-humans) and panzootic (a disease affecting animals of many species, especially over a wide area), killing tens of millions of birds and spurring the culling of hundreds of millions of other birds in an attempt to control its spread. In Epizoology, an epizootic (from Greek epi- upon + zoion animal is a Disease that appears as new cases in a given animal population Culling is the 'selection' (removal and killing of surplus animals from an animal population Most references in the media to "bird flu" and most references to H5N1 are about this specific strain. ^[109][110]

At present, HPAI A(H5N1) is an avian disease, and there is no evidence suggesting efficient human-to-human transmission of HPAI A(H5N1). In almost all cases, those infected have had extensive physical contact with infected birds. ^[111] In the future, H5N1 may mutate or reassort into a strain capable of efficient human-to-human transmission. Due to its high lethality and virulence, its endemic presence, and its large and increasing biological host reservoir, the H5N1 virus was the world's pandemic threat in the 2006–07 flu season, and billions of dollars are being raised and spent researching H5N1 and preparing for a potential influenza pandemic. Virulence (also called pestiferousness) refers to the degree of Pathogenicity of a Microbe, or in other words the relative ability of a Microbe In Epidemiology, an Infection is said to be endemic (from Greek en- in or within + demos people in a Population when Note For information about the content tone and sourcing of this article please see the tags at the bottom of this page ^[112]

Economic impact

Further information: Social impact of H5N1

Influenza produces direct costs due to lost productivity and associated medical treatment, as well as indirect costs of preventative measures. Financial According to the New York Times, due to the H5N1 threat as of March 2006 "governments worldwide have spent billions planning Variable costs are expenses that change in proportion to the activity of a business Productivity in Economics refers to measures of output from production processes per unit of input Indirect costs are costs that are not directly accountable to a particular function or product these are fixed costs In the United States, influenza is responsible for a total cost of over $10 billion per year, while it has been estimated that a future pandemic could cause hundreds of billions of dollars in direct and indirect costs. ^[113] However, the economic impacts of past pandemics have not been intensively studied, and some authors have suggested that the Spanish influenza actually had a positive long-term effect on per-capita income growth, despite a large reduction in the working population and severe short-term depressive effects. The 1918 flu pandemic (commonly referred to as the Spanish flu) was an Influenza Pandemic that spread to nearly every part of the world A recession is a contraction phase of the Business cycle. The U ^[114] Other studies have attempted to predict the costs of a pandemic as serious as the 1918 Spanish flu on the U.S. economy, where 30% of all workers became ill, and 2. The Economy of the United States is the largest national economy in the world 5% were killed. A 30% sickness rate and a three-week length of illness would decrease the gross domestic product by 5%. Additional costs would come from medical treatment of 18 million to 45 million people, and total economic costs would be approximately $700 billion. ^[115]

Preventative costs are also high. Governments worldwide have spent billions of U. S. dollars preparing and planning for a potential H5N1 avian influenza pandemic, with costs associated with purchasing drugs and vaccines as well as developing disaster drills and strategies for improved border controls. Emergency management (or disaster management) is the discipline of dealing with and avoiding risks Border controls are measures used by a Country to monitor or regulate its Borders The control of the flow of people animals and goods across a border may be controlled ^[112] On November 1, 2005, President George W. Bush unveiled the National Strategy to Safeguard Against the Danger of Pandemic Influenza^[116] backed by a request to Congress for $7. Events 996 - Emperor Otto III issues a deed to Gottschalk Bishop of Freising which is the oldest known document using the name Ostarrîchi Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. George Walker Bush ( born July 6 1946 is the forty-third and current President of the United States. The United States Congress is the bicameral Legislature of the federal government of the United States of America, consisting of two houses 1 billion to begin implementing the plan. ^[117] Internationally, on January 18, 2006, donor nations pledged US$2 billion to combat bird flu at the two-day International Pledging Conference on Avian and Human Influenza held in China. Events 350 - Generallus Magnentius deposes Roman Emperor Constans and proclaims himself Emperor Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. ^[118]

As of 2006, over ten billion dollars have been spent, and over two hundred million birds have been killed to try to contain H5N1 avian influenza. ^[119] However, as these efforts have been largely ineffective at controlling the spread of the virus, other approaches are being tried: for example, the Vietnamese government in 2005 adopted a combination of mass poultry vaccination, disinfecting, culling, information campaigns and bans on live poultry in cities. Vietnam (ˌviːɛtˈnɑːm Việt Nam) officially ^[120] As a result of such measures, the cost of poultry farming has increased, while the cost to consumers has gone down due to demand for poultry falling below supply. This has resulted in devastating losses for many farmers. Poor poultry farmers cannot afford mandated measures which isolate their bird livestock from contact with wild birds (among other measures), thus risking losing their livelihood altogether. Multinational poultry farming is increasingly becoming unprofitable as H5N1 avian influenza becomes endemic in wild birds worldwide. ^[121] Financial ruin for poor poultry farmers, which can be as severe as threatening starvation, has caused some to commit suicide and many others to stop cooperating with efforts to deal with this virus—further increasing the human toll, the spread of the disease, and the chances of a pandemic mutation. ^[122][123]

See also

• Virus
• List of viruses
• List of epidemics

Information concerning flu research can be found at

References and notes

Further reading

External links

• Info on influenza at CDC
• Influenza (Mayo Clinic)
• Fact Sheet Overview of influenza at World Health Organization
• Health encyclopedia entry at NHS Direct
• BioHealthBase Bioinformatics Resource Center Database of influenza sequences and related information. The Centers for Disease Control and Prevention (or CDC) is an agency of the United States Department of Health and Human Services based in unincorporated NHS Direct is the name of a 24 hour confidential Telephone, Online and interactive digital TV health advice and information service provided by the National
• Overview of influenza at MedicineNet
• Congressional Research Service (CRS) Reports regarding Influenza Law-related government reports at University of North Texas
• Influenza Surveillance and Contingency Plans (by country/region)
• Orthomyxoviridae The Universal Virus Database of the International Committee on Taxonomy of Viruses
• Influenza Virus Resource from the NCBI
• InfluenzaWorld Resource for all influenza-related information. WebMD is a medical and wellness information service primarily known for its public Internet site which provides health information a symptom checklist pharmacy information blogs of The International Committee on Taxonomy of Viruses ( ICTV) is a committee which authorizes and organizes the taxonomic classification of Viruses They have The National Center for Biotechnology Information ( NCBI) is part of the United States National Library of Medicine (NLM a branch of the National Institutes
• European Influenza Surveillance Scheme
• Review of Influenza origin, virology, clinical syndromes and management from thenakedscientists. com at Cambridge University Pathology Dept.