Curious Folks Ask: 162 Real Answers on Amazing Inventions, Fascinating Products, and Medical Mysteries by Sherry Seethaler

Author:Sherry Seethaler [Seethaler, Sherry]
Language: eng
Format: epub, mobi, pdf
Tags: Reference, Science, Education, Technology & Engineering, Health & Fitness, Health, Teaching Methods & Materials, Human body, Diseases, Applied Sciences, Science & Technology, Questions & Answers, Curiosities & Wonders, Consumer goods, Chemical engineering, Inventions, Miscellanea, Technology
ISBN: 9780137057382
Publisher: FT Press
Published: 2010-02-18T10:00:00+00:00

Influenza viruses do evolve particularly quickly. Vaccine strains used against influenza must be changed at least every two to three years, because the proteins on the virus surface keep changing, thereby disguising it from the immune system. Vaccines against polio and many other human viruses have been stable for decades.

Part of what determines how fast a virus mutates is the type of genetic material it uses. Some viruses have genomes consisting of DNA. A chemically similar molecule, RNA, serves as the genetic material for other viruses. Another type of virus, the retrovirus, has RNA as its genetic material but copies RNA into DNA within an infected cell.

As a general rule, DNA viruses mutate more slowly than retroviruses, which mutate more slowly than RNA viruses. The fastest-mutating RNA virus has a mutation rate about 100,000 times faster than the slowest-mutating DNA virus. This range reflects the accuracy and proofreading ability of the machinery used to copy the different types of genetic material.

The genome of the variola (smallpox) virus is DNA, and a comparison of 45 virus samples from around the world during the 30 years prior to the eradication of smallpox revealed little sequence diversity. Yet genetic spellchecking is not the whole story, because polio, measles, and influenza are all caused by RNA viruses.

The mutation rate in viruses is also influenced by their generation time, genomic architecture (how the DNA or RNA is folded and whether it is single- or double-stranded), viral and host enzymes, and opportunities for virus particles to exchange genetic material with one another.

Yet higher mutation rates do not always enhance evolution. In an experiment in which the mutation rate of poliovirus was artificially increased by a factor of 10, the production of the virus decreased 1,000-fold, probably the result of an error catastrophe. In fact, increasing mutation rates to a lethal level is the mechanism of some antiviral drugs, such as ribavirin, a treatment for hepatitis C.

Therefore, mutation rate is insufficient to explain why influenza is a master of disguise compared to other RNA viruses, and the specific constraint on the evolution of surface protein variation remains a mystery.

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