A vector is an organism that acts as a carrier of pathogenic disease or bacteria which is then transmitted from one host to another; the disease or bacteria is dormant in the vector and does not threaten its survival. Vector-borne
diseases are a chief health threat globally. They infect more than one billion people a year and cause more than one million deaths.
Vectors contain mosquitoes, fleas, cockroaches, flies and rodents. Vector also includes eye gnats. In addition, diseases once thought to be restricted to certain areas are appearing in the same vectors. Some disasters provide
rise to increases in the populations of vector or nuisance species, usually insects or rodents. Floods may make new mosquito breeding sites in disaster rubble and stagnant pools.