a carrier, especially an arthropod, that transfers an infective agent from one host (which can include itself) to another.


(i) Mechanical: includes simple mechanical carriage by a crawling or flying insect through soiling of its feet or proboscis, or by passage of organisms through its gastrointestinal tract. This does not require multiplication or development of the organism. (ii) Biological: propagation (multiplication), cyclic development, or a combination of these (cyclopropagative) is required before the arthropod can transmit the infective form of the agent to humans. An incubation period (extrinsic) is required following infection before the arthropod becomes infective. The infectious agent may be passed vertically to succeeding generations (transovarian transmission); transstadial transmission indicates its passage from one stage of life cycle to another, as nymph to adult. Transmission may be by injection of salivary gland fluid during biting, or by regurgitation or deposition on the skin of feces or other material capable of penetrating through the bite wound or through an area of trauma from scratching or rubbing. This transmission is by an infected nonvertebrate host and not simple mechanical carriage by a vector or vehicle. However, an arthropod in either role is termed a vector.


the degree of pathogenicity of an organism as evidenced by the severity of resulting disease and the organism’s ability to invade the host tissues.


causative agent of an infectious disease.

Xenogeneic infection

derived from, originating in, or being a member of another species.


transplantation of an organ, tissue, or cells between two different species (such as a human and a domestic swine).


an infection or infectious disease transmissible under natural conditions from vertebrate animals to humans. May be enzootic or epizootic.

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