A biological vector is an animal or arthropod that transfers a pathogen or parasite from one host to another. In this role the vector typically does not benefit from carrying the agent and may experience reduced fitness. The term is most often applied to creatures that move infectious organisms — for example, the process of transport of microbes or parasites — rather than to every incidental contact between species.
Types and key characteristics
Vectors are commonly divided into two broad categories. Mechanical vectors carry infectious material on their bodies or mouthparts and transfer it passively (for example, flies that pick up bacteria on their legs). Biological vectors support part of the pathogen's development or replication within the vector's body before transmission to a new host; many mosquitoes fall into this category. Important properties include vector competence (ability to acquire and transmit a specific agent), feeding behavior, lifespan, and population density.
Examples and life cycle interactions
Classic examples include mosquitoes that transmit malaria and dengue: some species of mosquito provide the environment in which parasites or viruses develop before they are passed to humans. See also malaria and dengue fever. Other vectors are ticks (which transmit bacterial and viral infections), fleas (historically associated with plague), sandflies (leishmaniasis), and triatomine bugs (Chagas disease). The study of how pathogens circulate between vector, reservoir hosts and human victims — the life cycle of a disease agent — is central to controlling transmission.
Vectors are distinct from reservoirs (species that harbor a pathogen over long periods) and from incidental or dead-end hosts, which do not contribute meaningfully to onward spread. Research in medical entomology and vector ecology examines these relationships and the environmental factors that shape them.
Control, surveillance and public-health importance
Because vectors mediate transmission of many major infectious diseases, public-health efforts focus on reducing contact between vectors and people and limiting vector populations. Typical measures include insecticide-treated bed nets, habitat modification to remove breeding sites, indoor residual spraying, personal protection, and surveillance programs. Understanding vector behavior and distribution — for example, the habits of certain mosquitoes or the seasonal activity of ticks — guides intervention strategies and outbreak response.
Several broad factors influence vector-borne disease risk: urbanization, human movement, climate and land-use changes can alter vector ranges and seasonality. Pathogen evolution and the emergence of insecticide resistance are additional challenges. Effective control combines entomological knowledge, epidemiology and community-level actions to reduce disease burdens linked to vectors and to interrupt cycles of parasites and pathogens that cause disease.