Microscopically small, extremely pathogenic particles (lat. virus = mucus, juice, poison), which are among the most dangerous enemies of many plants and also of the vine. Simple viruses usually consist of a protein shell and nucleic acid enclosed in it (in contrast to the proteinless viroids). All viruses contain the programme (some viruses also contain other auxiliary components) for their reproduction and spread. They do not consist of a cell and therefore do not possess independent replication nor their own metabolism and are therefore dependent on the metabolism of a host cell such as a bacterium. According to common doctrine, viruses are not to be counted as living organisms, but they can at least be considered "close to life". So far, 3,000 different species have been identified, but probably many more exist. They are only viable on the living tissue of a host and re-function its metabolism. The contents of the host cell are completely dissolved and degenerate into a malignant cell.
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