Virology is the branch of science that studies viruses and virus-like agents—including their structure, classification, genetics, methods of infection, replication, and the diseases they cause. Key Concepts: Viruses: Microscopic infectious agents that can replicate only inside living cells of organisms. They are not considered fully "alive" because they lack cellular structure and metabolism. Hosts: Viruses infect all forms of life—humans, animals, plants, fungi, and even bacteria (these are called bacteriophages). Viral Structure: Most viruses consist of: A genetic core (DNA or RNA) A protein coat (capsid) Some have an outer lipid envelope derived from the host cell What Virologists Do: Study how viruses infect cells Understand how viruses spread and evolve Develop vaccines and antiviral drugs Monitor and control viral outbreaks (e.g., COVID-19, influenza, HIV, etc.) Common Viral Diseases: Influenza (flu) HIV/AIDS COVID-19 (SARS-CoV-2) Hepatitis Herpes Measles, Mumps, Rubella