A vector is an animal that transmits disease. For instance the mosquito is a vector for malaria, and ticks are vectors for rocky mountain spotted fever.
A vector-borne disease is an infection that requires the participation of some other factor (vector) that actively infects successive victims. For Example: Malaria, yellow fever and West Nile Virus...
It could have previously been infected by a virus, where the virus DNA is inserted into the cell, causing it to explode and reproduce hundreds of viruses. Or it could carry it like any other animal.
A vector-borne disease is one in which the pathogenic microorganism is transmitted from an infected individual to another individual by an arthropod or other agent, sometimes with other animals...