DNA and RNA: Viruses.

Essay by trenchfighterJunior High, 9th gradeA-, August 2003

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Viruses have been with us since the very beginning of life; probably from when we first arose as a species (they would have been evolving right along with us). These formidable agents of infection don't survive in the fossil record but evidence from ancient civilisations reveals some of the long history we've reluctantly shared with them.

Egyptian drawings dating back to around 1400BC depict people with the wasted legs characteristic of poliomyelitis, or polio, a viral disease that often causes paralysis of the limbs. Smallpox causes scars that can still be seen on the mummy of Ramses 5th, who died in 1157BC.

Some 3000 years later, in the 1790s, English country doctor Edward Jenner developed the worlds first reliable vaccine against smallpox when he noticed that people who contracted the minor ailment of cowpox were immune to the much more serious disease of smallpox. Jenner deliberately began infecting people with cowpox to fight smallpox.

The human fight to stop viral infection through the application of science had begun.

Jenner did not actually know that he was fighting a virus, the word wasn't even in use then. However it was around this time and through the following century that the microscope began opening up the previously unknown world of the microbe. Fungi, protozoa and bacteria that had previously been invisible because they were so small were now being identified and described, and humankind was beginning to understand their connection with infectious diseases.

In the 1880s, fine filters made of porcelain were developed that could screen bacteria from solutions. When it became clear that some infectious agents could pass through even these fine filters, the term 'filterable virus' came into use. They were microbes that could cause disease but still couldn't be seen with even the most powerful light microscope. The word...