"Transmission" - what is it, definition of the term
The conveyance of pathogens by ectoparasites—including ticks, insects, lice, and fleas—occurs when these organisms acquire infectious agents from an infected host and subsequently introduce them into a new host during feeding or physical contact, thereby enabling the spread of disease across individual organisms and larger populations.
Detailed information
Arthropod vectors such as ticks, true bugs, lice, and fleas facilitate the movement of pathogens from animal reservoirs to humans or between humans. The process involves the ingestion of infected blood, attachment to a new host, and subsequent release of microorganisms through saliva, feces, or body fluids.
Ticks attach for several days, during which they secrete anticoagulants and immunomodulatory compounds. These secretions create a conduit for bacteria, viruses, and protozoa to enter the host’s bloodstream. Common agents transmitted by ticks include Borrelia burgdorferi (Lyme disease), Rickettsia spp. (spotted fever), and Anaplasma phagocytophilum (anaplasmosis). Transmission efficiency rises with prolonged feeding and is amplified by co‑feeding on multiple hosts.
True bugs, particularly those in the Reduviidae family, acquire pathogens while feeding on infected vertebrates. The subsequent bite injects saliva containing the organism. Notable diseases spread by these insects are Chagas disease (Trypanosoma cruzi) and various hemorrhagic fevers caused by Rickettsia species. Salivary proteins facilitate pathogen survival and entry into the host’s circulatory system.
Lice sustain a life cycle entirely on human hosts. Body lice ingest blood laden with Rickettsia prowazekii (epidemic typhus) or Borrelia recurrentis (relapsing fever). The excreta of lice, contaminated with these microorganisms, become a source of infection when scratched into skin abrasions. Head lice rarely transmit disease but serve as mechanical carriers for bacterial agents.
Fleas, especially the cat flea (Ctenocephalides felis) and the rat flea (Xenopsylla cheopis), feed rapidly, injecting saliva that contains anticoagulants and enzymes. This saliva can harbor Yersinia pestis (plague) and Rickettsia typhi (murine typhus). Flea feces, rich in viable pathogens, pose an additional risk when they contaminate skin lesions or mucous membranes.
Key measures to limit vector‑mediated spread:
- Regular inspection and removal of ectoparasites from humans and domestic animals.
- Use of approved acaricides, insecticides, or repellents on skin, clothing, and habitats.
- Maintenance of environmental hygiene to reduce breeding sites (e.g., bedding changes, pet grooming).
- Prompt treatment of infected hosts to lower pathogen load available to vectors.
Understanding the biological interactions between these arthropods and the microorganisms they carry enables targeted interventions that disrupt the conduit of pathogen movement.