What is a virus?
A virus is a biological agent that carries genetic material inside a protein coat and uses a host cell’s machinery to reproduce. Some also have an outer envelope. Viruses differ from bacteria in structure, replication and treatment.
Structure and replication
A viral genome may be DNA or RNA, enclosed by a protein capsid. The virus attaches to a suitable cell, delivers its genetic material or enters, and uses cellular resources to make new viral components. Components assemble and new viruses are released. Host range depends on cell binding and intracellular conditions; no virus infects every species or tissue. Bacteria reproduce using their own cellular structures, whereas viruses have no independent metabolism or cellular reproduction.
Disease, prevention and research
Finding a virus does not always mean severe disease; outcomes depend on host immunity, exposure and viral properties. Vaccines can prepare immune defenses, while antivirals target particular steps in a viral life cycle. Antibiotics do not directly act against viruses, although a clinician may prescribe them for an accompanying bacterial infection. Some viruses change quickly, making monitoring and vaccine updates important. The relevance of hand hygiene, ventilation or vector control depends on the route of transmission. Viruses are also studied in gene delivery and biological research.