parasitische

Parasitische (German for parasitic) describes a relationship or characteristic in which one organism—the parasite—benefits at the expense of another—the host. Parasitism is a form of symbiosis that ranges from relatively harmless to harmful, and it occurs across living systems, including animals, plants, and microorganisms. The parasite often relies on the host for nutrients, habitat, or transmission to new hosts, and the interaction can influence host health, population dynamics, and ecosystem structure.

Parasites are broadly categorized by their location relative to the host: endoparasites live inside the host’s body (for example, Plasmodium, tapeworms, many protozoa), while ectoparasites inhabit the surface or external tissues (such as fleas, lice, ticks). They may be obligate, requiring a host to complete their life cycle, or facultative, able to pursue a parasitic lifestyle but also capable of free-living existence.

Many parasites have specialized adaptations to exploit hosts and evade immune defenses, including complex life cycles with multiple hosts, immune evasion strategies, or attachment structures. Parasitic plants operate similarly by extracting water and nutrients from host plants, sometimes via specialized structures called haustoria.

Examples of parasitic organisms include protozoans such as Plasmodium (the malaria parasite), Toxoplasma gondii, helminths such as cestodes and trematodes, and arthropods such as fleas and ticks. The study of parasitism spans medicine, veterinary science, ecology, and agriculture, focusing on transmission, host range, disease impact, and methods of control.