"Infection" - what is it, definition of the term
Pathogenic invasion denotes the colonization and replication of microorganisms within a host, resulting in tissue damage and physiological disruption. The event is initiated when vectors such as ticks, bugs, lice, or fleas transfer bacteria, viruses, or parasites during feeding, thereby breaching protective barriers. After entry, the agent exploits host resources, evades immune defenses, and provokes inflammatory responses that manifest as clinical symptoms. Diagnosis depends on identifying the causative organism, while control strategies emphasize vector avoidance and appropriate antimicrobial treatment.
Detailed information
Pathogen transmission by arthropod vectors represents a major route for acquiring bacterial, viral, and protozoan diseases. Ticks, true bugs, lice, and fleas each possess distinct biological traits that influence the efficiency and spectrum of microbial spread.
Ticks attach to a host for extended periods, inserting a cement-like saliva that contains anticoagulants and immunomodulatory proteins. This environment facilitates the transfer of spirochetes, flaviviruses, and rickettsiae. Notable agents include Borrelia burgdorferi (Lyme disease), Anaplasma phagocytophilum (human granulocytic anaplasmosis), and tick‑borne encephalitis virus. The life cycle involves three developmental stages—larva, nymph, adult—each requiring a blood meal, thereby expanding the geographic range of pathogens.
True bugs, such as bed bugs (Cimex lectularius) and assassin bugs (Triatoma spp.), can harbor Trypanosoma cruzi (Chagas disease) and various bacterial species. Their piercing‑sucking mouthparts penetrate skin, delivering saliva that may contain infectious agents. Although bed bugs are primarily associated with dermatitis, experimental evidence shows potential for mechanical transmission of viral particles.
Lice comprise three primary groups: head lice, body lice, and pubic lice. Body lice (Pediculus humanus corporis) are recognized vectors of Rickettsia prowazekii (epidemic typhus), Borrelia recurrentis (relapsing fever), and Coxiella burnetii (Q fever). Transmission occurs when infected feces contaminate skin abrasions during scratching. Head lice rarely act as disease carriers, but their prevalence serves as an indicator of hygiene and socioeconomic conditions.
Fleas, especially the cat flea (Ctenocephalides felis) and the rat flea (Xenopsylla cheopis), transmit Yersinia pestis (plague), Rickettsia typhi (murine typhus), and Bartonella henselae (cat‑scratch disease). Their rapid blood‑feeding cycles and ability to jump between hosts enable swift dissemination of pathogens across animal and human populations.
Key agents associated with each vector:
- Ticks: Borrelia burgdorferi, Anaplasma phagocytophilum, tick‑borne encephalitis virus
- True bugs: Trypanosoma cruzi, assorted bacteria
- Lice: Rickettsia prowazekii, Borrelia recurrentis, Coxiella burnetii
- Fleas: Yersinia pestis, Rickettsia typhi, Bartonella henselae
Effective control strategies focus on interrupting the vector life cycle, applying acaricides or insecticides, and reducing host exposure through personal protective measures. Monitoring vector populations and pathogen prevalence remains essential for early detection and mitigation of disease outbreaks.