Parasitic

Parasitic is an adjective used to describe a relationship or characteristic in which one organism benefits at the expense of another, the host. In biology, the term specifically refers to parasitism, a type of symbiotic relationship where a parasite lives on or inside a host and obtains resources from it. Parasites can be endoparasites, living inside the body, or ectoparasites, living on the surface. They often have complex life cycles that may involve multiple hosts or specific environmental conditions.

Biological parasites span diverse groups, including protozoa, helminths (such as flatworms and nematodes), and arthropods (such as ticks, fleas, and lice). Transmission methods vary and can include ingestion of contaminated food or water, vector-borne transfer by insects, direct contact, or penetration of the skin. Some parasites can alter host physiology or behavior to improve their own survival or transmission.

Parasitic infections have substantial health and economic impacts, causing malnutrition, anemia, organ damage, and impaired development in humans and animals. Public health responses focus on sanitation, vector control, vaccination where available, and antiparasitic medications. The emergence of drug resistance and the complexity of life cycles complicate control efforts.

Outside biology, parasitic is also used to describe unwanted, resource-consuming influences in other systems. In electronics and engineering, parasitic elements such as stray capacitance, inductance, or resistance can create interference or timing errors and are typically minimized in design and layout. In a broader sense, the term may be used metaphorically to denote dependencies that drain resources without offering commensurate benefits.

Etymology: from Greek parasitos, “one who eats at the table,” from para “beside” and sitos “food.” Related terms include parasite and parasitism.