Occurrence of major vector-borne disease is closely related to naturally existing environmental conditions. Changes in the climate and ecological changes due to engineering projects like dam-building can also have profound effects on rates of vector-borne and zoonotic diseases. The incidence, severity, and distribution of vector borne diseases are affected substantially by human activities.

- In 1997, an avian strain of influenza that had not previously infected humans began to kill healthy person in Hong Kong. Pandemic strains of influencza have emerged from swine reservoirs.

- A new variant of a fatal neurologic illness, Creutzfeldt-Jacob disease appeared in the UK and was transmitted by ingestion of beef from animals afflicted with bovine spongiform encephalopathy, also known as “Mad Cow Disease.”

- The number of cases of rabies diagnosed in humans in the United States has increased significantly since 1990, with most of the increase associated with bats.

USDHHS (1998), Preventing Emerging Infectious Diseases: A Strategy for the 21st Century, Atlanta: Centers for Disease Control and Prevention.