First: Definition Virus A virus is a non-living microscopic agent outside the host cell. It cannot perform any vital function on its own and depends entirely on the host cell for replication; therefore, it is considered an obligate intracellular parasite. Bacteria Bacteria are single-celled living microorganisms capable of independent growth and reproduction in various environments such as water, soil, and the human body. Some are beneficial, while others are pathogenic. Second: Size and Visibility • Viruses are much smaller than bacteria and are measured in nanometers. • Bacteria can be seen using a light microscope. • Viruses can only be observed using an electron microscope. Third: Structure and Composition Virus: • Genetic material: DNA or RNA • Protein coat (capsid) • Sometimes surrounded by a lipid envelope Viruses lack: • Nucleus • Cytoplasm • Ribosomes Bacteria: A complete cell structure that includes: • Cell wall • Cell membrane • Cytoplasm • Ribosomes • Sometimes flagella for movement • Circular DNA not enclosed within a nuclear membrane Fourth: Reproduction Virus: • Enters the host cell • Hijacks the cell’s machinery • Forces it to produce new viral particles • Viruses exit either by cell lysis or without destroying the cell Bacteria: • Reproduce independently through binary fission • Can double in number every 20 minutes under suitable conditions • Do not require a permanent host Fifth: Diseases Caused Viral diseases: • Influenza • COVID-19 • Viral hepatitis • AIDS • Measles Bacterial diseases: • Bacterial tonsillitis • Food poisoning • Urinary tract infections • Wound infections • Tuberculosis Sixth: Treatment Viruses: • Antibiotics are completely ineffective • Treatment depends on: • Supporting the immune system • Antiviral drugs (depending on the virus) • Vaccines for prevention Bacteria: • Treated using antibiotics • The choice of antibiotic depends on: • The type of bacteria • Its sensitivity to the drug Seventh: Prevention Prevention of viral infections: • Vaccination • Hand hygiene • Wearing masks during outbreaks • Avoiding direct contact Prevention of bacterial infections: • Personal hygiene • Proper wound disinfection • Drinking clean water • Maintaining food hygiene Hasan Najeh Al-Mustaqbal University The First University in Iraq.