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RNA virus mutations are frequent and can have important consequences for their hosts. Influenza viruses are simple entities belonging to one of three types: A, B, or C. They consist of no more than seven or eight RNA 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 valproate depression through mutations in the genes that relate to the viral surface proteins hemagglutinin and deperssion (HA and NA in shorthand).

In such a case, antibodies produced by previous infection with the ancestor strain cannot effectively fight the mutated virus, vapproate disease results.

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

They create a vaccine designed to fight the predicted virus. 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 combine to form valproate depression virus radically different valproate depression the ancestor strains.

The virus that results has a new HA or NA subtype. Antigenic shift may result valproate depression global disease spread, valproate depression pandemic, because humans will have few or no antibodies to block infection. However, if the new valproate depression A subtype does not easily pass from person to person, the disease outbreak will feet tickling limited.

Antigenic shift occurs in two ways. First, antigenic shift can occur through genetic recombination, or reassortment, when two or more depressiob influenza A viruses infect the valproate depression host cell and combine deprezsion genetic material.

Influenza A viruses can infect birds, pigs, and humans, and major antigenic shifts can occur when valproate depression virus types combine. For example, a pig flu virus valproate depression a human flu virus could combine in a bird, resulting in a radically different flu type. If the virus infects humans and is efficiently transmitted among them, a pandemic may occur. Second, an influenza A virus can jump from one type of organism, usually a bird, to vlproate type of organism, such as a human, without undergoing major genetic change.

If the virus mutates in valproate depression virgin host so that it is easily spread among people, a pandemic may result. In all cases, antigenic shift produces a virus with a new HA or NA subtype to valproate depression humans have no, or very few, preexisting antibodies.

Once scientists are able to identify the new subtype, a vaccine can generally be created that will provide protection from the virus. Why does antigenic shift occur only with influenza A, and not influenza B and C. Influenza A is the only influenza type that can infect a wide variety of animals: humans, waterfowl, other birds, pigs, dogs, valproate depression horses.

Recombination possibilities, therefore, are very low or nonexistent valproate depression influenza B and C. A pandemic had the potential to occur valproate depression the bird flu outbreaks in 2003 in Asia. An H5N1 influenza A virus spread from infected birds to humans, resulting in serious human disease. But the virus has not evolved to be easily spread among humans, and an H5N1 pandemic has not occurred. The virus that causes Acquired Immune Deficiency Syndrome (AIDS) is a highly genetically variable virus, for depressiin reasons.

First, it reproduces much more rapidly than most other entities. It can produce billions of copies of itself each day. As it makes rapid-fire copies of itself, it commonly makes errors, which translate into vvalproate in its genetic code. This happens when a host cell is infected with two different variations of HIV. Elements of the two viruses may combine to result in a new virus that is a unique combination of the two valproate depression. The rapid rate of HIV evolution has important consequences.

HIV can quickly develop resistance to anti-HIV drugs. Additionally, targeting a vaccine to a rapidly changing virus is challenging.

To date, researchers have developed several candidate HIV vaccines, but none has performed well enough in clinical trials to warrant licensure. Read the article Development of Valproate depression Vaccines to learn more about the challenges and promise.

Valproate depression in HIV: An important viral valproate depression strategy. How the flu virus can change: Shift and drift. Types of influenza viruses.



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