Or by a reduction in prevalence of some other disease vector?

This was the first demonstration that an arthropod could act as a disease vector to transmit an infectious agent to a vertebrate host.

Public health measures were ineffective because the role of the mosquito as a disease vector was then unknown.

And the spirit of solidarity can easily curdle into one where we continue to spy on our neighbours and see others primarily as disease vectors.

Very often the disease vectors were local, usually insects.