Viruses differ from all other infectious organisms in their structure and biology, particularly in their reproduction. Although viruses carry conventional genetic information in their DNA or RNA, they lack the synthetic machinery necessary for this information to be processed into new virus material.
The classification of viruses into major families is based upon a few simple criteria. These include:
- the type of nucleic acid in the genome;
- the number of nucleic acid strands and their polarity;
- the mode of replication;
- the size, structure and symmetry of the virus particle.
