"Vector-borne disease" is the term commonly used to describe an illness caused by an infectious microbe that is transmitted to people by blood-sucking arthropods. The arthropods (insects or arachnids) that most commonly serve as vectors include: 1.) blood sucking insects such as mosquitoes, fleas, lice, biting flies and bugs, and 2.) blood sucking arachnids such as mites and ticks. The term “vector” refers to any arthropod that transmits a disease through feeding activity.

Vectors typically become infected by a disease agent while feeding on infected vertebrates (e.g., birds, rodents, other larger animals, or humans), and then pass on the microbe to a susceptible person or other animal. In almost all cases, an infectious microbe must infect and multiply inside the arthropod before the arthropod is able to transmit the disease through its salivary glands. The most common vector-borne diseases in Virginia are carried by mosquitoes and ticks.