Influenza pathophysiology: Difference between revisions
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===Antigenic drift=== | ===Antigenic drift=== | ||
<small><small>'''Adapted from CDC '''<ref name=change>{{cite web|url=http://www.cdc.gov/flu/about/viruses/change.htm| title=CDC Seasonal Influenza - How the Flu Virus Can Change: “Drift” and “Shift”}} </ref></small></small> | |||
These are small changes in the genes of influenza viruses that happen continually over time as the virus replicates. These small genetic changes usually produce viruses that are pretty closely related to one another, which can be illustrated by their location close together on a phylogenetic tree. Viruses that are closely related to each other usually share the same antigenic properties and an immune system exposed to an similar virus will usually recognize it and respond. (This is sometimes called cross-protection.) | These are small changes in the genes of influenza viruses that happen continually over time as the virus replicates. These small genetic changes usually produce viruses that are pretty closely related to one another, which can be illustrated by their location close together on a phylogenetic tree. Viruses that are closely related to each other usually share the same antigenic properties and an immune system exposed to an similar virus will usually recognize it and respond. (This is sometimes called cross-protection.) | ||
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===Antigenic Shift=== | ===Antigenic Shift=== | ||
<small><small>'''Adapted from CDC '''<ref name=change>{{cite web|url=http://www.cdc.gov/flu/about/viruses/change.htm| title=CDC Seasonal Influenza - How the Flu Virus Can Change: “Drift” and “Shift”}} </ref></small></small> | |||
Antigenic shift is an abrupt, major change in the influenza A viruses, resulting in new hemagglutinin and/or new hemagglutinin and neuraminidase proteins in influenza viruses that infect humans. Shift results in a new influenza A subtype or a virus with a hemagglutinin or a hemagglutinin and neuraminidase combination that has emerged from an animal population that is so different from the same subtype in humans that most people do not have immunity to the new (e.g. novel) virus. Such a “shift” occurred in the spring of 2009, when an H1N1 virus with a new combination of genes emerged to infect people and quickly spread, causing a pandemic. When shift happens, most people have little or no protection against the new virus. | Antigenic shift is an abrupt, major change in the influenza A viruses, resulting in new hemagglutinin and/or new hemagglutinin and neuraminidase proteins in influenza viruses that infect humans. Shift results in a new influenza A subtype or a virus with a hemagglutinin or a hemagglutinin and neuraminidase combination that has emerged from an animal population that is so different from the same subtype in humans that most people do not have immunity to the new (e.g. novel) virus. Such a “shift” occurred in the spring of 2009, when an H1N1 virus with a new combination of genes emerged to infect people and quickly spread, causing a pandemic. When shift happens, most people have little or no protection against the new virus. | ||
Revision as of 17:42, 28 October 2014
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]
Overview
Pathophysiology
- Most healthy adults may be able to infect other people beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick.
- Children may pass the virus for longer than 7 days.
- Symptoms start 1 to 4 days after the virus enters the body.
- That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Some people can be infected with the flu virus but have no symptoms. During this time, those persons may still spread the virus to others.
- Influenza viruses are constantly changing. They can change in two different ways, the antigenic drift and the antigenic shift.
Antigenic drift
Adapted from CDC [1] These are small changes in the genes of influenza viruses that happen continually over time as the virus replicates. These small genetic changes usually produce viruses that are pretty closely related to one another, which can be illustrated by their location close together on a phylogenetic tree. Viruses that are closely related to each other usually share the same antigenic properties and an immune system exposed to an similar virus will usually recognize it and respond. (This is sometimes called cross-protection.)
But these small genetic changes can accumulate over time and result in viruses that are antigenically different (further away on the phylogenetic tree). When this happens, the body’s immune system may not recognize those viruses.
This process works as follows: a person infected with a particular flu virus develops antibody against that virus. As antigenic changes accumulate, the antibodies created against the older viruses no longer recognize the “newer” virus, and the person can get sick again. Genetic changes that result in a virus with different antigenic properties is the main reason why people can get the flu more than one time. This is also why the flu vaccine composition must be reviewed each year, and updated as needed to keep up with evolving viruses.
Antigenic Shift
Adapted from CDC [1] Antigenic shift is an abrupt, major change in the influenza A viruses, resulting in new hemagglutinin and/or new hemagglutinin and neuraminidase proteins in influenza viruses that infect humans. Shift results in a new influenza A subtype or a virus with a hemagglutinin or a hemagglutinin and neuraminidase combination that has emerged from an animal population that is so different from the same subtype in humans that most people do not have immunity to the new (e.g. novel) virus. Such a “shift” occurred in the spring of 2009, when an H1N1 virus with a new combination of genes emerged to infect people and quickly spread, causing a pandemic. When shift happens, most people have little or no protection against the new virus.
While influenza viruses are changing by antigenic drift all the time, antigenic shift happens only occasionally. Type A viruses undergo both kinds of changes; influenza type B viruses change only by the more gradual process of antigenic drift.
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Transmission
Adapted from CDC [2]
- People with influenza infection can spread the disease to others up to about 6 feet away.
- Most experts think that influenza viruses are spread mainly by droplets made when people with flu cough, sneeze or talk.
- These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.
- Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth or nose.
- To avoid this, people should stay away from sick people and stay home if sick.
- It also is important to wash hands often with soap and water.
- If soap and water are not available, use an alcohol-based hand rub.
- Linens, eating utensils, and dishes belonging to those who are sick should not be shared without washing thoroughly first.
- Eating utensils can be washed either in a dishwasher or by hand with water and soap and do not need to be cleaned separately. Further, frequently touched surfaces should be cleaned and disinfected at home, work and school, especially if someone is ill.