Viruses need a host to reproduce because viruses cannot replicate alone; they are categorized as parasitic organisms. Viral infections spread by entering a human, animal or bacterial cell. The virus inserts its genetic material into the host and takes over. After infecting the cell, the virus continues to reproduce - the cell begins making viral proteins instead of healthy cells. The viral protein and genetic materials mix to create more viruses, then escape to start over again, destroying the occupied cells.
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