parasitismi

Parasitism is a type of symbiotic relationship in which a parasite benefits from exploiting a host, often to the host’s detriment. The parasite uses the host as a source of resources such as nutrients, habitat, or transmission to new hosts, while the host bears costs that can include reduced fitness or increased disease risk. Parasitism spans many organisms, from viruses and protozoa to helminths and arthropods, and can be categorized as endoparasitism (inside the host) or ectoparasitism (on the outside). It can be obligate (required for the parasite’s life cycle) or facultative (capable of living freely but able to exploit a host).

Parasites exhibit diverse life cycles and strategies. Many have complex lifecycles that involve multiple hosts; for example, Plasmodium species cycle between humans and Anopheles mosquitoes, while tapeworms such as Taenia spp. involve intermediate and definitive hosts. Transmission methods include vectors, ingestion of contaminated food or water, direct contact, or skin penetration. Parasites can be intracellular or extracellular, feeding on host tissues, blood, or nutrients, and may be permanent residents or temporary visitors.

Ecological and evolutionary aspects of parasitism are central to its study. Parasitism influences population dynamics and community structure, and hosts evolve defenses such as immune responses and behavioral changes, while parasites develop countermeasures like immune evasion and antigenic variation. This ongoing coevolution is discussed in the Red Queen hypothesis. Parasitism has significant health, economic, and ecological impacts, including human diseases (for example, malaria), animal health issues, and agricultural losses.

Parasitology is the scientific discipline dedicated to studying parasites, their hosts, and interactions. Detection and study rely on microscopy, serology, and molecular methods. Control strategies emphasize sanitation and water treatment, vector management, vaccination where possible, and antiparasitic drugs, though resistance and ecological considerations pose ongoing challenges.