Virology is that the subject involved with the study of the biology of viruses and infective agent diseases, as well as the distribution, organic chemistry, physiology, biological science, ecology, evolution and clinical aspects of viruses. medical specialty is that the study of viruses, complexes of nucleic acids and proteins that have the capability for replication in animal, plant and microorganism cells. to copy themselves, viruses usurp functions of the host cells on that they're parasites. The viral parasite causes changes within the cell, notably its antigenicity; furthermore, guiding the host cell's metabolism to the assembly of latest virus particles could cause cellular death. Virally-induced death, changes in antigenicity and therefore the response of the host to the presence of the virus results in the manifestations of infective agent illness.