"Parasitism" - what is it, definition of the term
A parasitic relationship is a biological interaction where one organism exploits another for nutrients, shelter, or other resources, causing detriment to the host while gaining a survival advantage; this mode of life is exemplified by arthropods such as ticks, bugs, lice, and fleas, which possess specialized structures and life‑cycle strategies that enable them to attach to, feed on, and persist on their hosts.
Detailed information
Ticks are arachnids that attach to vertebrate hosts to obtain blood. Their life cycle typically includes egg, larva, nymph, and adult stages; each active stage requires a blood meal before molting. Host selection varies among species: Ixodes scapularis prefers small mammals in the larval stage and larger mammals as an adult, while Dermacentor variabilis shows broader host range. Salivary secretions contain anticoagulants and immunomodulatory proteins that facilitate prolonged feeding and enable transmission of pathogens such as Borrelia burgdorferi, Rickettsia rickettsii, and Anaplasma phagocytophilum. Control strategies focus on habitat management, acaricide application, and regular inspection of animals and humans.
True bugs, particularly Cimex lectularius (the bed bug), feed exclusively on blood. Adult females lay 1–5 eggs per day, depositing them in hidden crevices. Nymphs undergo five molts, each requiring a blood meal. Feeding occurs at night, with rapid engorgement lasting several minutes. Saliva contains anesthetic and vasodilatory compounds that mask the bite. Although bed bugs are not proven vectors of human disease, their presence causes dermatological reactions and psychological distress. Effective control combines heat treatment, insecticide rotation, and meticulous sanitation.
Lice are obligate ectoparasites of mammals and birds. Three major groups affect humans: head lice (Pediculus humanus capitis), body lice (Pediculus humanus corporis), and pubic lice (Pthirus pubis). Eggs (nits) are cemented to hair shafts and hatch within 7–10 days. Nymphs mature after three molts, feeding several times daily. Body lice can transmit Rickettsia prowazekii, Borrelia recurrentis, and Bartonella quintana. Management includes mechanical removal of nits, topical pediculicides, and improvement of personal hygiene and clothing hygiene for body lice.
Fleas are wingless, laterally compressed insects adapted for jumping. The cat flea (Ctenocephalides felis) and human flea (Pulex irritans) represent common species. Female fleas lay 20–50 eggs per day; eggs fall off the host into the environment, where larvae develop in organic debris. Adult fleas feed on blood, injecting anticoagulants and anti-inflammatory agents. Vector competence includes Yersinia pestis, Rickettsia felis, and Bartonella henselae. Integrated pest management combines environmental sanitation, insecticide-treated bedding, and regular treatment of host animals.
Key points summarizing host‑exploiting arthropods:
- Life cycles involve egg, immature, and adult stages, each requiring a blood meal.
- Salivary compounds facilitate feeding and pathogen transmission.
- Disease agents transmitted include bacteria (Borrelia, Rickettsia), protozoa (Bartonella), and viruses (rarely).
- Control relies on environmental management, chemical interventions, and personal hygiene.