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Viruses are genetic entities that lie somewhere in the gray area between living and non-living states. Viruses consist of genetic material (DNA or RNA) encased in a protective protein shell, come in many different shapes and are many times smaller than bacteria ranging 20 to 400 nanometers in diameter. As viruses lack the biosynthetic machinery that is necessary for metabolic function and reproduction, in order for a virus to replicate it must find and infect a suitable host cell, which then mistakes the virus for a protein and replicates its genetic code. These viral infections often cause diseases in humans and animals. Learn more about viruses, their types, life-cycles and effects on human health in this book.

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