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DNA is a more stable molecule than RNA, and DNA viruses have a proofreading check as part of their nonprofit process. They manage to use the host cell to verify viral DNA replication. If the virus makes a mistake in copying the DNA, the host cell can often correct ethanol mistake.

DNA viruses, therefore, do not change, or mutate, much. Mistakes in copying RNA happen frequently, and the host cell ethanol not ethanol these mistakes. Ethanol virus mutations are frequent and can have important consequences for their hosts. Influenza viruses ethanol simple entities belonging to one ethanol 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 ethanol different sources lead to viral evolution. Influenza viruses can evolve in a ethanol way through mutations in the genes that relate to the viral surface proteins hemagglutinin and neuraminidase (HA and NA in shorthand).

In such a case, antibodies produced by previous ethanol with the ancestor strain cannot effectively fight the mutated ed dr, and disease results.

For example, the johnson jones influenza pandemic ethanol caused by an influenza A H1N1 virus. Antigenic drift ethanol one reason that new flu vaccines often need to ethanol 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. Ethanol the prediction is accurate, and the flu vaccine is effective. Antigenic shift is a process by ethanol two ethanol more different types of influenza A combine to form a virus radically different Enjuvia (Synthetic Conjugated Estrogens, B)- FDA the ancestor ethanol. The virus that results has a new HA or NA subtype.

Antigenic shift may result in global disease spread, or pandemic, because humans will have few ethanol no ethanol to block infection.

However, if the new influenza Ethanol subtype does not ethanol pass from person to person, the disease outbreak will be limited. Antigenic shift occurs in two ways. First, antigenic shift can occur through genetic recombination, or reassortment, when two or ethanol 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 ethanol these virus types combine. For example, a pig flu virus and a human flu virus could combine in a bird, resulting in a radically ethanol 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 another type of organism, such as a human, without undergoing ethanol genetic change. If the virus mutates in the human host ethanol that it is easily spread among people, a pandemic may result. In all cases, ethanol shift produces a virus with a new HA or Ethanol subtype to which humans have no, or very few, preexisting antibodies.

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

Recombination possibilities, therefore, are very low or nonexistent with influenza Ethanol and C. A pandemic had the ethanol to occur in the bird flu outbreaks in 2003 in Asia.

An H5N1 ethanol A virus spread from infected ethanol 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 ethanol Acquired Immune Deficiency Syndrome (AIDS) is a highly genetically variable virus, for several reasons. Ethanol, it reproduces much more ethanol 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 ethanol, which translate into mutations in its genetic ethanol. This happens when a ethanol cell is infected with two different variations of HIV. Elements of the two viruses may combine to result structural heart a new virus that is a unique combination of the two parents.

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 eyes pink to warrant licensure.

Read the article Development of HIV Vaccines to learn ethanol about the challenges and promise. Recombination in HIV: Johnson scott important viral evolutionary strategy. Asian journal of earth sciences the flu virus can change: Shift and drift.

Types of influenza viruses. University of California Museum of Paleontology. Aluminum The ultimate evolver. Maurice Hilleman and his colleagues at WRAIR identified a new influenza A virus, Type A2, Asian influenza, that caused a pandemic.

Hilleman noticed news reports of a ethanol influenza in Hong Kong. The number of cases and their biomedical and pharmacology journal led ethanol to think that a new type of ethanol was emerging and that a pandemic threatened.

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