This unit builds on the basic concepts of virology taught at Level 2. It focuses on human and animal viruses associated with disease. The lecture topics which are taught in the unit include features of virus structure; genetics and cultivation; viral taxonomy; the main viral diseases of humans; the replication cycle of the RNA and DNA viruses; genetically controlled interactions between viruses and the host; and the host immune response and the mechanisms by which certain viruses cause disease. The unit also discusses the emergence of new viral diseases, the role of insect vectors and the re-emergence of existing viral diseases together with the surveillance measures which are used to track the movement of viruses locally and globally. The control of viral diseases including the use of vaccines, antiviral drugs and other measures are also presented.