"Carrier" - what is it, definition of the term
A vector is an organism that harbors a pathogen without exhibiting disease symptoms and facilitates its passage to another host; ticks, insects, lice, and fleas acquire microorganisms during blood meals and subsequently introduce them into new hosts via later bites, thereby acting as biological agents of disease transmission.
Detailed information
Vectors such as ticks, true bugs, lice, and fleas serve as biological conduits for a wide range of pathogens. Their capacity to acquire, maintain, and disseminate microorganisms depends on specific physiological traits, feeding behavior, and ecological interactions.
Ticks attach to mammals, birds, or reptiles for prolonged blood meals, creating a stable environment for the replication of bacteria, viruses, and protozoa. Their multi‑stage life cycle (egg, larva, nymph, adult) allows sequential host switching, which can bridge wildlife reservoirs and domestic animals. Salivary secretions contain anti‑coagulant and immunomodulatory compounds that facilitate pathogen transmission during feeding.
True bugs (Hemiptera) include species such as bed bugs and assassin bugs. Some feed on vertebrate blood and can mechanically transfer pathogens present on their mouthparts. Others, like triatomine bugs, harbor intracellular parasites that develop within the gut and are released in feces, entering the host through mucous membranes or skin abrasions.
Lice (Pediculus and Phthirus) are obligate ectoparasites of humans and other mammals. Their limited mobility confines transmission to direct contact or shared personal items. Certain lice species support the replication of rickettsial agents, which are expelled with feces and can enter the host through scratching.
Fleas (Siphonaptera) are wingless, laterally compressed insects that jump between hosts. Their digestive tract can support the growth of bacteria such as Yersinia pestis, which are released into the host’s bloodstream during blood ingestion. Flea larvae develop in environments rich in organic debris, allowing indirect transmission cycles involving rodents and domestic animals.
Key disease agents associated with these arthropods include:
- Borrelia spp. (Lyme disease) – transmitted primarily by Ixodid ticks.
- Rickettsia spp. (typhus, spotted fever) – associated with lice, fleas, and certain bugs.
- Bartonella spp. (cat‑scratch disease, trench fever) – linked to fleas and lice.
- Trypanosoma cruzi (Chagas disease) – vectored by triatomine bugs.
- Yersinia pestis (plague) – spread by fleas.
Control strategies focus on interrupting the vector’s life cycle: acaricides for ticks, insecticide‑treated fabrics for lice, environmental sanitation to reduce flea breeding sites, and habitat modification to limit bug populations. Surveillance programs monitor vector density and pathogen prevalence, enabling timely public‑health interventions.