A vector in public health is an organism, typically an insect or arthropod, that carries and transmits infectious pathogens between humans or from animals to humans. This transmission facilitates the spread of diseases such as malaria, dengue, and Lyme disease. Unlike contaminated surfaces or genetic mutations, vectors actively transfer the pathogen from an infected host to a susceptible one, making them crucial targets in disease control and prevention strategies. Understanding vectors is essential for interrupting disease transmission cycles.

Reference: Harrison's Principles of Internal Medicine, Kasper et al., 20th Edition.