Pathogenicity refers to the ability of an organism, such as a bacterium, virus, or fungus, to cause disease in a host. This capability depends on various factors, including the organism's genetic makeup, its ability to invade host tissues, and the mechanisms it uses to evade the host's immune system. Different pathogens exhibit varying levels of pathogenicity, which can be influenced by the host's health, age, and immune response. Understanding pathogenicity is crucial for developing treatments and preventive measures against infectious diseases, as it helps identify how pathogens interact with their hosts.