Infectious Diseases

How Flu Viruses Combine to Form a new Virus



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All viruses mutate, or combine their genetic material in new forms. In the process, they can create what to the human immune system are essentially new viruses, or more accurately new strains of existing viruses, to which the body's immune system has not prepared a defence. The reason that influenza - and, in a similar way, the common cold - is so potentially dangerous is that it is particularly adept at recombining its genetic material, with new influenza outbreaks occurring every year.

- About Viral Genetic Change -

Viruses mutate all the time, although the particular rate of change depends on how the virus is made up and therefore varies considerably between different types of viruses. Two very common ailments, influenza and cold viruses, are particularly known for their rapid mutations and genetic changes. The common cold is so adept at developing new combinations of its genetic material, for example, that all attempts thus far to develop a vaccine or therapy for the cold have not been effective. In contrast, the flu virus is versatile but somewhat more versatile, allowing partially effective annual vaccines and frequently effective post-exposure treatments such as Tamiflu.

In essence, despite the differences, all viruses operate in the same way when it comes to combining to form new viruses. Like other life forms, their genetic material is in a constant state of flux, as viruses meet and exchange genetic material, and as mutations therefore have opportunities to spread and become common. This is, in effect, the same process as all other life undergoes. However, since the viral replication cycle is both very rapid compared to animals and also involves much larger numbers (millions of copies of a virus can infect a single organism), this means that there is both a much greater propensity for mutations and new combinations to develop, as well as a much shorter timeline for those new combinations to become common viral traits rather than unusual exceptions.

- About Flu Virus Mutations -

Flu viruses combine to form new and dangerous viral outbreaks in two forms. Influenza occurs in several dominant subtypes - the current swine flu pandemic, for example, was a mutation of what is known as the H1N1 influenza, while the more feared avian flu outbreak, should it ever occur, will be drawn from the H5N1 flu. In addition, it is dispersed across several different animal species reservoirs, in particular humans, pigs, and birds. (A fourth and less common flu reservoir is the horse.)

Mutations giving rise to new and dangerous flu viruses occur in one of two forms. First, they may result from viruses combining and forming new combinations of genetic material within a particular species. This is the most common source of the large number of variations in flu genetic material which occur yearly, and which the pharmaceutical companies responsible for producing vaccines attempt to guess as they prepare their annual fall flu vaccines.

Second, and more seriously, flu viruses may emerge when viruses combine across normal species barriers: that is, when influenza viruses present in humans, pigs, and/or birds meet and combine. Usually, a flu virus infecting one species cannot spread between members of another (for example, swine flu normally does not spread between humans); however, when the correct mutations and recombinations occur, such spread may become possible. For example, the H1N1 pandemic of 2009-2010, although known by the name "swine flu," was actually a combination of genetic material drawn from swine, bird, and human flu strains. Such species-crossing outbreaks are particularly dangerous because the new population often has little or no immunity to the new virus, and is therefore at greater risk of harm.

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