👉 Infections are caused by the invasion and multiplication of pathogens—such as bacteria, viruses, fungi, or parasites—within a host organism, disrupting normal physiological functions and leading to disease. The primary demands of an infection involve the pathogen's ability to breach the body's defenses, which include physical barriers like skin and mucous membranes, as well as immune responses like inflammation and the activation of white blood cells. Pathogens must evade or suppress these defenses to establish and proliferate. Once inside, they exploit host resources for survival and reproduction, often triggering symptoms such as fever, pain, and tissue damage. Effective infection demands include successful colonization, replication, and transmission, either to new hosts or within the same host, ultimately leading to clinical manifestations that can range from mild to severe, depending on the pathogen's virulence and the host's immune status.
