H1N1 Virus

The 2009 flu pandemic is a global outbreak of a new strain of H1N1 influenza virus, often referred to as "swine flu" in the media. Although the virus, first detected in April 2009, contains a combination of genes from swine, avian (bird), and human influenza viruses, it cannot be spread by eating pork or pork products.

The outbreak began in Veracruz, Mexico, with evidence that there had been an ongoing epidemic for months before it was officially recognized as such. The Mexican government closed most of Mexico City's public and private facilities in an attempt to contain the spread of the virus. However the virus continued to spread globally, clinics were overwhelmed by people infected, and the World Health Organization (WHO) and US Centers for Disease Control (CDC) stopped counting cases and in June declared the outbreak to be a pandemic.

While only mild symptoms are experienced by the majority of people, some have more severe symptoms. Mild symptoms may include fever, sore throat, cough, headache, muscle or joint pains, and nausea, vomiting, or diarrhea. Those at risk of a more severe infection include: asthmatics, diabetics, those with obesity, heart disease, the immunocompromised, children with neurodevelopmental conditions, and pregnant women. In addition, even for persons previously very healthy, a small percentage of patients will develop viral pneumonia or acute respiratory distress syndrome. This manifests itself as increased breathing difficulty and typically occurs 3?6 days after initial onset of flu symptoms.. About 50 percent of swine flu hospitalizations globally and about 70 percent of those in the United States seem to involve underlying conditions.

Similar to other influenza viruses, pandemic H1N1 is typically contracted by person to person transmission through respiratory droplets. Symptoms usually last 4?6 days. To avoid spreading the infection, it is recommended that those with symptoms stay home, away from school, work, and crowded places. Those with more severe symptoms or those in an at risk group may benefit from antivirals (oseltamivir or zanamivir). As of December 27 the WHO reported 12,220 confirmed deaths worldwide. WHO http://www.who.int/csr/don/2009_12_30/en/index.html This figure is a sum of confirmed deaths reported by national authorities and the WHO states that total mortality (including deaths unconfirmed or unreported) from the new H1N1 strain is "unquestionably higher" than this. The CDC estimates that, in the USA alone, and as of November 14, there had been 9,820 deaths (range 7,070-13,930) caused by swine flu.

A pandemic (from Greek ??? pan "all" + ????? demos "people") is an epidemic of infectious disease that is spreading through human populations across a large region; for instance a continent, or even worldwide. A widespread endemic disease that is stable in terms of how many people are getting sick from it is not a pandemic. Further, flu pandemics exclude seasonal flu, unless the flu of the season is a pandemic. Throughout history there have been a number of pandemics, such as smallpox and tuberculosis. More recent pandemics include the HIV pandemic and the 2009 flu pandemic.

Influenza A (H1N1) virus is a subtype of influenza A virus and the most common cause of influenza (flu) in humans. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza. H1N1 strains caused a few percent all human flu infections in 2004?2005. Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza).

In June 2009, World Health Organization declared that flu due to a new strain of swine-origin H1N1 was responsible for the 2009 flu pandemic. This strain is often called swine flu by the public media.

Category: File - :1918 flu outbreak2.jpg|thumb|300px|Two American Red Cross nurses demonstrate treatment practices during the influenza pandemic of 1918.

The 1918 flu pandemic (commonly referred to as the Spanish Flu) was an influenza pandemic that spread to nearly every part of the world. It was caused by an unusually virulent and deadly influenza A virus strain of subtype H1N1. Historical and epidemiological data are inadequate to identify the geographic origin of the virus. Most of its victims were healthy young adults, in contrast to most influenza outbreaks which predominantly affect juvenile, elderly, or otherwise weakened patients. The flu pandemic has also been implicated in the sudden outbreak of encephalitis lethargica in the 1920s.

The pandemic lasted from March 1918 to June 1920,Institut Pasteur. La Grippe Espagnole de 1918 (Powerpoint presentation in French). spreading even to the Arctic and remote Pacific islands. It is estimated that anywhere from 50 to 100 million people were killed worldwide which is from three to seven times the casualties of the First World War (15 million), making it the most deadly natural disaster in human history.Centers for Disease Control and Prevention. Jeffery K. Taubenberger and David M. Morens. 1918 Influenza: the Mother of All Pandemics, January, 2006. Retrieved on May 9, 2009. Archived 2009-10-01.Tindall 2007The 1918 Influenza Pandemic. Accessed 2009-05-01. Archived 2009-05-04. An estimated 50 million people, about 3% of the world's population (approximately 1.6 billion at the time), died of the disease. An estimated 500 million, or 1/3 were infected.

Scientists have used tissue samples from frozen victims to reproduce the virus for study. Given the strain's extreme virulence there has been controversy regarding the wisdom of such research. Among the conclusions of this research is that the virus kills via a cytokine storm (overreaction of the body's immune system) which explains its unusually severe nature and the concentrated age profile of its victims. The strong immune systems of young adults ravaged the body, whereas the weaker immune systems of children and middle-aged adults caused fewer deaths.

:For the H5N1 subtype of Avian influenza see Influenza A virus subtype H5N1.

Avian influenza, sometimes avian flu, and commonly bird flu, refers to "influenza caused by viruses adapted to birds." "Avian influenza strains are those well adapted to birds"EUROPEAN CENTRE FOR DISEASE PREVENTION AND CONTROL. Chapter Two : Avian Influenza by Timm C. Harder and Ortrud Werner in Influenza Report 2006Large-scale sequencing of human influenza reveals the dynamic nature of viral genome evolution Nature magazine presents a summary of what has been discovered in the Influenza Genome Sequencing Project.Avian Influenza A (H5N1) Infection in Humans by The Writing Committee of the World Health Organization (WHO) Consultation on Human Influenza A/H5 in the September 29, 2005 New England Journal of MedicineThe Threat of Pandemic Influenza: Are We Ready? Workshop Summary (2005) Full text of online book by INSTITUTE OF MEDICINE OF THE NATIONAL ACADEMIES[http://www.cdc.gov/ncidod/EID/vol11no10/05-0644-G1.htm] CDC has a phylogenetic tree showing the relationship between dozens of highly pathogenic varieties of the Z genotype of avian flu virus H5N1 and ancestral strains.Evolutionary characterization of the six internal genes of H5N1 human influenza A virus Of the greatest concern is highly pathogenic avian influenza (HPAI).

"Bird flu" is a phrase similar to "swine flu," "dog flu," "horse flu," or "human flu" in that it refers to an illness caused by any of many different strains of influenza viruses that have adapted to a specific host. All known viruses that cause influenza in birds belong to the species influenza A virus. All subtypes (but not all strains of all subtypes) of influenza A virus are adapted to birds, which is why for many purposes avian flu virus is the influenza A virus (note that the "A" does not stand for "avian").

Adaptation is non-exclusive. Being adapted towards a particular species does not preclude adaptations, or partial adaptations, towards infecting different species. In this way strains of influenza viruses are adapted to multiple species, though may be preferential towards a particular host. For example, viruses responsible for influenza pandemics are adapted to both humans and birds. Recent influenza research into the genes of the Spanish flu virus shows it to have genes adapted to both birds and humans; with more of its genes from birds than less deadly later pandemic strains.

Human flu is a term used to refer to influenza cases caused by Orthomyxoviridae that are endemic to human populations (as opposed to infection relying upon zoonosis). It is an arbitrary categorization scheme, and is not associated with phylogenetics-based taxonomy. Human flu-causing viruses can belong to any of three major influenza-causing Orthomyxoviruses ? Influenza A virus, Influenza B virus and Influenza C virus.

The annually updated trivalent influenza vaccine contains two hemagglutinin (HA) surface glycoprotein components from Influenza A virus strains and one from B influenza.

Most human flu is a non-pandemic flu that is slightly different from the main human flus that existed in last year's flu season period. This type of flu is also called "common flu" or "seasonal flu" or "annual flu". It causes yearly flu epidemics that are generally not deadly except to the very old or very young.

Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Influenzavirus A includes only one species: Influenza A virus which causes influenza in birds and some mammals. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon. Some isolates of influenza A virus cause severe disease both in domestic poultry and, rarely, in humans. Occasionally viruses are transmitted from wild aquatic birds to domestic poultry and this may cause an outbreak or give rise to human influenza pandemics.

Influenza A viruses are negative sense, single-stranded, segmented RNA viruses.

There are several subtypes, labeled according to an H number (for the type of hemagglutinin) and an N number (for the type of neuraminidase). There are 16 different H antigens (H1 to H16) and nine different N antigens (N1 to N9). The newest H type (H16) was isolated from black-headed gulls caught in Sweden and the Netherlands in 1999 and reported in the literature in 2005.CIDRAP - Center for Infectious Disease Research And Policy Pandemic Influenza Overview

Each virus subtype has mutated into a variety of strains with differing pathogenic profiles; some pathogenic to one species but not others, some pathogenic to multiple species.

Influenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called "Influenza B virus".

Influenza B viruses are only known to infect humans and seals, giving them influenza. This limited host range is apparently responsible for the lack of Influenzavirus B caused influenza pandemics in contrast with those caused by the morphologically similar Influenzavirus A as both mutate by both genetic drift and reassortment.

Further diminishing the impact of this virus "in man, influenza B viruses evolve slower than A viruses and faster than C viruses". Influenzavirus B mutates at a rate 2-3 times lower than type A. However, influenza B mutates enough that lasting immunity is not possible. For example at the U.S.'s Food and Drug Administration's (FDA) Center for Biologics Evaluation and Research's Vaccines and Related Biological Products Advisory Committee's 101st meeting of February 16, 2005, an extensive discussion and vote was held concerning next year's flu vaccine virus selection including which influenza B strain to use in the formulation of the flu vaccine:

"For Influenza B, the question was asked: are there new strains present? And the answer was yes, and in 2004, the majority of the viruses were similar to a strain called B/Shanghai/361/2002, which is from the so-called B/Yamagata/1688 hemagglutinin lineage. That lineage was not the one that was being used in the vaccine that was current last year. In a minority of the strains that were found during the epidemiological studies were similar to the strain that was in the vaccine for last year, which was B/Hong Kong/330/2001, which belongs to the HA lineage that we represent with the strain B/Victoria/287. In answer to the question were these new viruses spreading, the answer, of course, is definitely yes. The Fujian-like viruses had become widespread around the world and were predominant everywhere, and these B/Shanghai-like strains at the time we were holding this meeting in February were predominant not only in North America and the United States, but also in Asia and Europe."Transcript of U.S. FDA Center for Biologics Evaluation and Research Vaccines and Related Biological Products Advisory Committee's 101st meeting of February 16, 2005. origin.www.fda.gov DOC format Google provided HTML format

Influenzavirus C is a genus in the virus family Orthomyxoviridae, which includes those viruses which cause influenza. The only species in this genus is called "Influenza C virus".

Influenza C viruses are known to infect humans and pigs, giving them influenza. Flu due to the type C species is rare compared to types A or B, but can be severe and can cause local epidemics.

Types A and B have 8 RNA segments and encode 11 proteins. Subtype C has 7 RNA segments and encodes 9 proteins.