Infectious diseases are illnesses brought on by pathogenic microorganisms, which might include bacteria, viruses, fungi, or parasites. These germs can spread from person to person, through tainted food or water, or through vectors like ticks or mosquitoes. Chronic diseases are long-term ailments that can endure for years or even a lifetime. They usually develop gradually over time. If neglected or inadequately managed, these illnesses frequently necessitate continuous care and can result in substantial morbidity and mortality. Epidemiology is the study of how health-related states or events are distributed throughout populations, how they are caused, and how to use this information to prevent and manage health issues.