unenveloped viruses they persist for months in the environment;
Growth in infected animals is slow , lesions may take weeks to appear;
2. They have not yet been grown in tissue culture; but molecular biology has
led to an explosion in knowledge of how they replicate;
3. They have early and late genes: the early genes [E genes] are associated with
4. Infectious virus [ or viral components] may be absent from the transformed cells.
5. Virus has a predilection for epithelial tissues.