👉 Infection is a complex biological process initiated when a pathogen, such as a bacterium, virus, fungus, or parasite, enters a host and begins to multiply or cause disease. Chemically, this process starts with the pathogen's ability to adhere to host cells, often through specific surface molecules that recognize and bind to receptors on the host cell membrane. This adhesion is crucial for the pathogen to gain entry, typically via endocytosis or direct penetration. Once inside, the pathogen may release enzymes or toxins that disrupt host cell functions, evade the immune system, or facilitate its replication. For example, viruses inject their genetic material into host cells, hijacking cellular machinery to produce more viral particles. Bacteria can produce toxins that damage host tissues or alter immune responses. The host's immune system responds by recognizing pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs), triggering an inflammatory response and activating immune cells like macrophages and T-cells to eliminate the invader. This intricate interplay of chemical interactions between pathogens and host cells defines the infection process, leading to either clearance of the pathogen or establishment of disease.
