Influenza suina 2010 Influenza suina Images

Infobox_Disease

Name=Influenza
Image=EM of influenza virus.jpg
Caption=TEM of negatively stained influenza virions, magnified approximately 100,000 times
Width=226
DiseasesDB=6791
ICD10=
ICD9=
MedlinePlus=000080
eMedicineSubj=med
eMedicineTopic=1170
eMedicine_mult=
MeshID=D007251
Influenza''', commonly referred to as the '''flu , is an infectious disease caused by RNA viruses of the family Orthomyxoviridae (the influenza viruses), that affects birds and mammals. The most common symptoms of the disease are chills, fever, sore throat, muscle pains, severe headache, coughing, weakness/fatigue and general discomfort.

cite web

url=http://www.merck.com/mmhe/sec17/ch198/ch198d.html
title=Influenza: Viral Infections: Merck Manual Home Edition
publisher=www.merck.com
accessdate=2008-03-15
last=
first=
Sore throat, fever and coughs are the most frequent symptoms. In more serious cases, influenza causes pneumonia, which can be fatal, particularly for the young and the elderly. Although it is often confused with other influenza-like illnesses, especially the common cold, influenza is a more severe disease than the common cold and is caused by a different type of virus. Typically, influenza is transmitted through the air by coughs or sneezes, creating aerosols containing the virus. Influenza can also be transmitted by direct contact with bird droppings or nasal secretions, or through contact with contaminated surfaces. Airborne aerosols have been thought to cause most infections, although which means of transmission is most important is not absolutely clear. As the virus can be inactivated by soap, frequent hand washing reduces the risk of infection. Influenza spreads around the world in seasonal epidemics, resulting in the deaths of between people every year, Vaccinations against influenza are usually given to people in developed countries The TIV carries no risk of transmitting the disease, and it has very low reactivity. A vaccine formulated for one year may be ineffective in the following year, since the influenza virus evolves rapidly, and new strains quickly replace the older ones. Antiviral drugs can be used to treat influenza, with neuraminidase inhibitors being particularly effective.

Classification

Types of influenza virus

. The hemagglutinin (HA) and neuraminidase (NA) proteins are shown on the surface of the particle. The viral RNAs that make up the genome are shown as red coils inside the particle and bound to Ribonuclear Proteins (RNPs). In virus classification influenza viruses are RNA viruses that make up three of the five genera of the family Orthomyxoviridae:
Influenzavirus A
Influenzavirus B
Influenzavirus C These viruses are only distantly related to the human parainfluenza viruses, which are RNA viruses belonging to the paramyxovirus family that are a common cause of respiratory infections in children such as croup, =

Influenzavirus A

= This genus has one species, influenza A virus. Wild aquatic birds are the natural hosts for a large variety of influenza A. Occasionally, viruses are transmitted to other species and may then cause devastating outbreaks in domestic poultry or give rise to human influenza pandemics. 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. The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are:
H1N1, which caused Spanish flu in 1918, and the 2009 flu pandemic
H2N2, which caused Asian Flu in 1957
H3N2, which caused Hong Kong Flu in 1968
H5N1, a current pandemic threat
H7N7, which has unusual zoonotic potential
H1N2, endemic in humans and pigs
H9N2
H7N2
H7N3
H10N7 =

Influenzavirus B

= (for a Fujian flu virus) This genus has one species, influenza B virus. Influenza B almost exclusively infects humans =

Influenzavirus C

= This genus has one species, influenza C virus, which infects humans, dogs and pigs, sometimes causing both severe illness and local epidemics.

Structure, properties, and subtype nomenclature

Influenzaviruses A, B and C are very similar in overall structure. Hemagglutinin (HA) and neuraminidase (NA) are the two large glycoproteins on the outside of the viral particles. HA is a lectin that mediates binding of the virus to target cells and entry of the viral genome into the target cell, while NA is involved in the release of progeny virus from infected cells, by cleaving sugars that bind the mature viral particles.

Replication

Viruses can only replicate in living cells. 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). Once inside the cell, the acidic conditions in the endosome cause two events to happen: first part of the hemagglutinin protein fuses the viral envelope with the vacuole's membrane, then the M2 ion channel allows protons to move through the viral envelope and acidify the core of the virus, which causes the core to dissemble and release the viral RNA and core proteins. These core 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). Negative-sense vRNAs that form the genomes of future viruses, RNA-dependent RNA polymerase, and other viral proteins are assembled into a virion. Hemagglutinin and neuraminidase molecules cluster into a bulge in the cell membrane. The vRNA and viral core proteins leave the nucleus and enter this membrane protrusion (step 6). The mature virus buds off from the cell in a sphere of host phospholipid membrane, acquiring hemagglutinin and neuraminidase with this membrane coat (step 7). 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. Drugs that inhibit neuraminidase, such as oseltamivir, therefore prevent the release of new infectious viruses and halt viral replication. After the release of new influenza viruses, the host cell dies. Because of the absence of RNA proofreading enzymes, the RNA-dependent RNA polymerase that copies the viral genome makes an error roughly every 10 thousand nucleotides, which is the approximate length of the influenza vRNA. Hence, the majority of newly manufactured influenza viruses are mutants; this causes "antigenic drift", which is a slow change in the antigens on the viral surface over time. The separation of the genome into eight separate segments of vRNA allows mixing or reassortment of vRNAs if more than one type of influenza virus infects a single cell. The resulting rapid change in viral genetics produces antigenic shifts, which are sudden changes from one antigen to another. These sudden large changes allow the virus to infect new host species and quickly overcome protective immunity. This is important in the emergence of pandemics, as discussed below in the section on Epidemiology.

Signs and symptoms

_ The first influenza virus to be isolated was from poultry, when in 1901 the agent causing a disease called "fowl plague" was passed through Chamberland filters, which have pores that are too small for bacteria to pass through. However, it was not until Wendell Stanley first crystallized tobacco mosaic virus in 1935 that the non-cellular nature of viruses was appreciated. The first significant step towards preventing influenza was the development in 1944 of a killed-virus vaccine for influenza by Thomas Francis, Jr.. This built on work by Australian Frank Macfarlane Burnet, who showed that the virus lost virulence when it was cultured in fertilized hen's eggs. 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. In comparison to vaccines, the development of anti-influenza drugs has been slower, with amantadine being licensed in 1966 and, almost thirty years later, the next class of drugs (the neuraminidase inhibitors) being developed.

Society and culture

Influenza produces direct costs due to lost productivity and associated medical treatment, as well as indirect costs of preventative measures. 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. 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. In an assessment of the 2009 H1N1 pandemic on selected countries in the Southern Hemisphere, data suggest that all countries experienced some time-limited and/or geographically isolated socio/economic effects and a temporary decrease in tourism most likely due to fear of 2009 H1N1 disease. It is still too early to determine whether the H1N1 pandemic has caused any long-term economic impacts.

Research

virus in a biosafety level 3 environment. 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). 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. 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. 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. 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 and has now successfully concluded Phase I clinical trials. A number of biologics, therapeutic vaccines and immunobiologics are also being investigated for treatment of infection caused by viruses. Therapeutic biologics are designed to activate the immune response to virus or antigens. Typically, biologics do not target metabolic pathways like anti-viral drugs, but stimulate immune cells such as lymphocytes, macrophages, and/or antigen presenting cells, in an effort to drive an immune response towards a cytotoxic effect against the virus. Infuenza models, such as murine influenza, are convenient models to test the effects of prophylactic and therapeutic biologics. For example, Lymphocyte T-Cell Immune Modulator inhibits viral growth in the murine model of influenza.

Infection in other animals

Influenza infects many animal species, and transfer of viral strains between species can occur. Birds are thought to be the main animal reservoirs of influenza viruses. On the other hand, outbreaks in pigs are common and do not cause severe mortality.

Bird flu

Flu symptoms in birds are variable and can be unspecific. 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. 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. This Asian lineage strain of HPAI A(H5N1) is spreading globally. 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. Most references in the media to "bird flu" and most references to H5N1 are about this specific strain. 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.

Swine flu

In pigs swine influenza produces fever, lethargy, sneezing, coughing, difficulty breathing and decreased appetite. In 2009, a swine-origin H1N1 virus strain commonly referred to as "swine flu" caused the 2009 flu pandemic, but there is no evidence that it is endemic to pigs (i.e. actually a swine flu) or of transmission from pigs to people, instead the virus is spreading from person to person.

See also

List of epidemics
List of viruses
Vitamin D and influenza ;Information concerning flu research can be found at:

References

Further reading

General

Bernd Sebastian Kamps, Christian Hoffmann and Wolfgang Preiser (Eds.) Influenza Report, 225 pp, PDF, free download. Flying Publisher 2006



ISBN 978-3-211-80892-4 The Influenza Viruses Hoyle L 1968 Springer Verlag History


Microbiology

Pathogenesis

Epidemiology


Epidemiology of WHO-confirmed human cases of avian influenza A(H5N1) infection Treatment and prevention

Research

WHO (PDF) contains latest Evolutionary "Tree of Life" for H5N1 article ''Antigenic and genetic characteristics of H5N1 viruses and candidate H5N1 vaccine viruses developed for potential use as pre-pandemic vaccines'' published 18 August 2006
WHO's assessment of Flu Research as of November 2006.

External links

ERS Online Course on Influenza
Swine and Seasonal Flu, Institute for Good Medicine at the Pennsylvania Medical Society
Info on influenza at CDC
Summary of the disease at the NYTimes.
10 Genes, Furiously Evolving NYTimes May 4, 2009
Outbreak Alerts United States based communicable disease notification website.
Influenza Research Database – Database of influenza genomic sequences, serotypes, polymorphisms, structures, epitopes, drugs and related tools.
Influenza (Mayo Clinic)
Fact Sheet Overview of influenza at World Health Organization
The Multinational Influenza Seasonal Mortality Study (MISMS) Fogarty International Center
Health encyclopedia entry at NHS Direct
Orthomyxoviridae The Universal Virus Database of the International Committee on Taxonomy of Viruses
Influenza Virus Resource from the NCBI
European Influenza Surveillance Scheme
Flu Trends – flu activity across the U.S.
[https://www.nhsdirect.nhs.uk/Sat/Topics/ColdsAndFlu.aspx?Host=Nhsd&SyndicationPartnerGuid=d19370ea-a100-407d-9695-b73407f701c7&TopicGuid=8c903315-a302-412a-bfae-9cb576d4b4cd Cold and flu advice] (NHS Direct)
Online video discussing influenza outbreaks and spread of other infectious diseases (Vega Science Trust)
Flu.gov: Know What To Do About the Flu
PATH Vaccine Resource Library influenza resources