How do biological vectors differ from mechanical vectors?

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In the context of infectious diseases, the primary difference between biological and mechanical vectors lies in the interaction between the pathogen and the vector.

Biological Vectors

In biological transmission, the infectious agent undergoes a necessary phase of development, change, or replication within the vector before it can be transmitted to a new host. For example, when a tick transmits the bacteria that cause Lyme disease, the pathogen undergoes specific changes in antigen expression while inside the vector.1

Mechanical Vectors

Mechanical vectors serve as passive carriers. The pathogen does not develop, change, or replicate inside the vector; instead, it is simply transported from one host or surface to another. A common example is the housefly, which may pick up bacteria like E. coli or Salmonella from waste and deposit them onto food, leading to illness when that food is consumed.1