Biological transmission via vectors is characterized by what?

• A. Requires multiplication, cyclic development, or both in the vector before transmission; includes extrinsic incubation period.
• B. Does not require multiplication or development inside the vector.
• C. Occurs only by mechanical transfer.
• D. Vector becomes infective immediately upon acquiring pathogen.

Answer: (A)

Biological transmission via vectors requires the pathogen to multiply or undergo development inside the vector before it can be transmitted to a new host. This internal change makes the vector an essential part of the pathogen’s life cycle. Because of this, there is an extrinsic incubation period—the time from when the vector acquires the pathogen to when the pathogen reaches the salivary glands or other transmissive sites and the vector becomes capable of transmitting it. Therefore, the vector is not infectious immediately after feeding.

Responses describing no multiplication or development inside the vector would be mechanical transmission, not biological. And saying the vector becomes infectious immediately would ignore the necessary maturation steps inside the vector.