👉 Infection begins when a pathogen, such as a virus or bacterium, enters the body through various routes of exposure, including respiratory droplets, contaminated surfaces, or direct contact with infected individuals or bodily fluids. Once inside, the pathogen must survive and replicate within host cells to establish an infection. This often involves evading the immune system's initial defenses, like physical barriers and immune cells, and then exploiting cellular machinery for its own propagation. The pathogen can then spread locally, causing tissue damage and symptoms, or enter the bloodstream (systemic infection), traveling to other parts of the body and potentially causing widespread illness. The severity and type of infection depend on factors such as the pathogen's virulence, the host's immune response, and environmental conditions.
