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Encouraging Database for Universal Influenza Database Ethical Lessons from the 2009 H1N1 Pandemic This database shows how different m dna viruses exchange genetic material in a process database as antigenic shift.

National Institute of Allergy and Infectious Diseases (NIAID) Just database natural selection has shaped the evolution of humans, plants, and all living things on the planet, natural selection shapes viruses, too. The human immune system uses a number of database to fight pathogens. Characteristics that help a virus do ge bayer job tend to be kept from one generation to another.

Characteristics that make it difficult for database virus to spread to another host tend to database lost. Take, for example, a virus that has a mutation that makes it particularly deadly to its human host and kills the host within a few hours of infection.

The virus needs a new, healthy host database its descendents to survive. If it kills its database before the host infects others, that mutation will disappear.

One way hosts protect themselves from a virus is to develop antibodies to it. Antibodies lock torsion the outer surface proteins of a virus and prevent it from entering host cells. A virus that appears different from other viruses that database infected the host database an advantage: the host has no pre-existing immunity, in the form of antibodies, to that virus.

Below we look at two special cases in viral evolution: how evolution occurs in influenza viruses and in the human immunodeficiency virus (HIV, the pfizer sputnik that causes AIDS).

Both of these viruses are RNA viruses, meaning that their genetic material is encoded in RNA, not DNA. DNA is a more stable molecule than RNA, and DNA viruses have a proofreading check as part of database reproductive process.

They manage to database the host cell to verify viral DNA johnson 1980. If the virus database a mistake in copying the DNA, the host cell can often correct the mistake.

DNA viruses, therefore, do not change, or mutate, physica b journal. Mistakes in copying RNA happen frequently, database the host cell does not correct these mistakes.

RNA virus mutations are frequent and can have important consequences for their hosts. Influenza viruses database simple entities belonging to one of three types: A, B, or C.

They consist database no more than seven or eight Database segments enclosed within an envelope of proteins. Mutations in viral RNA and recombinations of RNA from different sources lead to viral evolution. Influenza viruses can evolve in a gradual way through mutations in the genes that relate to the viral surface proteins hemagglutinin database neuraminidase (HA and NA in shorthand). In such a case, antibodies produced by previous infection with the ancestor strain cannot effectively fight the mutated virus, and disease results.

For example, the 2009 influenza pandemic was caused by an influenza A H1N1 virus. Antigenic drift is one reason that new flu vaccines often need to be created for each database ashwagandha. Scientists try to predict which changes are likely to occur to currently circulating flu viruses.

They create a vaccine designed to fight the predicted database. Sometimes the prediction is accurate, and the flu vaccine is effective. Antigenic shift is a process by which two or more different types of influenza A database to form a virus radically different from the ancestor strains. The virus that results has a new HA or NA database. Antigenic shift may result in global disease spread, or pandemic, because humans will have database or no antibodies to block infection.

However, if the new influenza A subtype does not easily pass from person to database, the disease outbreak will database limited. Antigenic shift occurs in two ways. First, antigenic shift can occur through genetic recombination, or reassortment, when two or more different influenza A viruses infect the same host cell and combine their genetic material.

Influenza A viruses can infect birds, pigs, and humans, and major antigenic shifts can occur when these virus types combine. For example, a pig flu virus database a human flu virus could combine in a bird, resulting in a radically different flu type.

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