Host–parasite interaction
A biological relationship in which a parasite lives on or in a host, gaining resources while reducing the host’s fitness.
Parasite life cycle: The sequence of developmental stages and host transitions through which a parasite reproduces and spreads. Life-cycle stages determine when parasites enter hosts, exploit them, and move onward.
Parasitism: An ecological interaction in which one organism benefits while harming another organism it exploits. Host–parasite interaction is the biological form of this broader ecological relationship.
Host–pathogen interaction: The relationship between a host and a disease-causing agent, including infection, defense, and damage. Pathogen-focused analysis emphasizes disease, while parasitism also includes non-disease-causing parasites.
Coevolution: Reciprocal evolutionary change between interacting species, each exerting selection on the other. Hosts and parasites can continually evolve in response to one another’s defenses and strategies.
Virulence: The degree to which a parasite reduces its host’s survival or reproductive success. Virulence captures the harm produced by exploitation, though it need not rise with parasite abundance.
Host: An organism that provides another organism with resources or habitat, including a parasite. The host supplies the environment and resources on which the parasite depends.
Zoonosis: An infectious disease that can spread between nonhuman animals and humans. Host shifts across species can create routes for infections to reach human populations.
Red Queen hypothesis: The idea that species must continually evolve to maintain fitness amid changes in interacting species. Host–parasite arms races can make ongoing adaptation necessary for both sides.
Host resistance: A host’s capacity to prevent infection or reduce a parasite’s burden. Resistance limits parasite establishment or reproduction, directly changing the interaction’s outcome.
Parasite: An organism that lives in or on another organism and obtains resources at its expense. The parasite gains resources while imposing costs on its host.