The original question was: I have been advised to have another “flu shot” because the flu virus is evolving, so I am no longer immune through last year’s shot. Also, how come people can get swine flu or bird flu if it has not evolved?
Answer by Diane Eager
The Influenza A virus certainly does undergo regular and sometimes rapid changes, and these alterations do enable it to cause epidemics in animals, birds and people, but none of these changes are evolution.
The most important way that viruses can change in a way that enables them to move to different hosts, e.g. pigs and people, is reassortment. This occurs when two varieties of the same species of virus infect the same host.
Whenever any virus infects a cell, the virus is ‘unpacked ‘ and its disassembled genes then take advantage of the cell’s machinery to manufacture more genes and recombine them to make large numbers of virus copies. However, if two differing viruses infect one cell, genes from each virus can be copied then mixed during the reassembly process producing new gene combinations that have never appeared before to our knowledge. Viral reassortment facilitates the movement of a virus between hosts.
Therefore, a bird flu virus and a human flu virus may meet in a pig and mix some genes, and the recombined bird/pig/human flu hybrid virus can now infect pigs, birds and humans. Since this never involves making new genes, but rather re-distributing genes that already exist. it is not evolution. The viruses start and finish the same Kind, but for the scientist and medics case the new combination ‘flu virus’ each receive a new label as “Influenza A Virus variation XYZ number ……..”.
Viruses can also change due to mutation, i.e. copying errors of their genes. Flu viruses are rather prone to this because their genetic information is stored on single strand of RNA instead of the more secure double stranded DNA with inbuilt backup. DNA has two complementary strands of code letters, so each strand can act as a means of cross checking the stored and copied information, but flu virus RNA has only one strand, so it has only one copy of each gene. When DNA is replicated an enzyme named DNA polymerase not only makes new copies, but also checks them for accuracy and edits any mistakes. The single strand RNA copying enzyme does not have such a check/edit function, so any mistakes are left uncorrected.
Some of these virus mutations change the information for their surface proteins, which results in the proteins having a slightly different shape. These surface proteins are the H and N numbers used to identify the particular strain or variety of the virus, e.g. H5N1. It is these surface proteins that the immune system responds to when a virus infects a person (or an animal or bird). The immune systems of an infected person does not recognise a mutated virus straight away, and the virus can successfully invade and reproduce, makes that person ill until their immune system can respond. This is why people are advised to have flu vaccines whenever a new flu outbreak is occurring.
Another type of viral mutation occurs which can change the activity level of genes involved in replicating the virus, so they replicate faster or slower. However they start and finish the same Kind of virus, so again it’s not evolution but if replication rate is increased you may feel a whole lot sicker.
All the changes above do cause small changes in already existing proteins, yet they do not explain the origin of the proteins, and the virus containing them never changes into anything but an Influenza A virus. The variations in the viruses are well documented, but they only reveal variation within the same virus, not a change to a new virus. For example see: Ecological and immunological determinants of influenza evolution, Nature 422, 428-433 (27 March 2003) doi:10.1038/nature01509.
Again it turns out the view from Darwin’s Glasses that is claimed to be evolution when the facts don’t show it all. Viewers have merely labelled any change in virus as evolution, than use that as proof of evolution, in order to grandly pronounce that virus could never have been created.
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