[Virusology at the begining of the XXI century].

Viral injections are the most common human diseases (especiaily acute respiratory infections, mostly in children and young adults). The current studies show that viral infections can cause not only acute, but persistent viral diseases as well. A certain number of viruses are able to incorporate their nucleic acid into the genome of the host-cell, leading to rearrangement of the cell genes and formation of malignant tumors. Viral persistence can cause manifiestations of latent or chronic infections, as well as prion-caused slow infections of the central nervous system. Defective Di particles play an important role in maintaining viral persistence. Viruses are important agents involved in various disorders of the immunological homeostasis of the organism. Newly-found viruses represent a special problem.