👉 Infection is a biological process where a pathogen, such as a bacterium, virus, fungus, or parasite, enters and establishes itself within a host organism, disrupting normal cellular functions and causing disease. This occurs when the pathogen breaches the body's defenses, often through openings like the skin or mucous membranes, and begins to multiply. The interaction between the pathogen and the host's immune system is crucial: while the immune system attempts to eliminate the invader, the pathogen may evade or manipulate these defenses, leading to inflammation, tissue damage, and the symptoms of infection. For example, a bacterium like Streptococcus pneumoniae can invade the respiratory tract, multiply, and trigger an immune response that results in pneumonia. Understanding infection mechanisms is vital for developing treatments and preventive measures.
