Parasiitide

Parasiitide are organisms that live in or on another organism, the host, from which they obtain nutrients and benefits at the host’s expense. They can be classified as endoparasites, which inhabit the body of the host, and ectoparasites, which cling to the exterior surfaces such as skin or feathers. Parasites differ from parasitoids in that most do not kill their hosts outright; disease and reduced fitness may occur, but many maintain long-term associations with their hosts.

Parasites span several biological groups. Protozoa like Plasmodium cause malaria, helminths such as cestodes (tapeworms) and nematodes (roundworms) inhabit hosts, and arthropods including ticks, fleas, lice, and mites act as ectoparasites or vectors. Many parasite life cycles are complex and involve multiple developmental stages or hosts, enabling transmission through vectors, contaminated food, or direct contact. The relationship between parasite and host can range from relatively benign to pathogenic, often shaping host behavior, physiology, and population dynamics.

Host–parasite interactions drive coevolution, with hosts evolving immune defenses and parasites developing strategies to evade them. Parasitism can influence health, reproduction, and survival and has broad ecological and economic consequences, including disease burdens in humans and production animals, as well as impacts on wildlife ecosystems.

Control and management rely on a combination of sanitation and public health measures, vector control, antiparasitic drugs, and vaccination where available. Understanding parasite biology and transmission is essential for prevention, diagnosis, and effective treatment, reducing the impact of parasitism on both humans and animals.