👉 Infection occurs when a pathogen, such as a virus, bacterium, or parasite, enters and establishes itself within a host organism, disrupting normal cellular functions and causing disease. The allocation of resources by the host to combat the infection involves a complex interplay of immune responses. Initially, the innate immune system, which includes physical barriers like skin and mucous membranes, as well as cells like macrophages and neutrophils, acts quickly to contain and neutralize the pathogen. If the infection persists, the adaptive immune system is activated, involving T cells and B cells that specifically target and destroy infected cells and produce antibodies to neutralize the pathogen. This allocation of resources—such as energy, nutrients, and signaling molecules—is crucial for the host's survival and recovery, though it can also lead to inflammation and tissue damage if not properly regulated.
