Smallpox was eradicated almost twenty years ago, leaving people to believe that infectious diseases could be beaten. However, since the smallpox elimination, no other disease has been similarly abolished. New diseases are having impact, and old diseases are developing resistance to medical technologies thought to have subdued them. Infectious and parasitic diseases, or IPDs, caused more than 17 million deaths in 1995, or more than a quarter of all human deaths.
Tuberculosis still remains the leading cause of adult death from infectious disease.
New and emerging diseases include HIV, Ebola, hantavirus, Hepatitis-C, the Legionella bacteria and the Cyclospora parasite. The main factor effecting the emergence and spread of new diseases is believed to be transportation. Elements include greater mobility between populations, the faster and easier transport of disease-carrying organisms across the world, the movement of people into environments where they had not been before, and altering those environments so that they are exposed to previously unencountered organisms. Another factor could be climate change. An increase in extreme weather events increases disease incidents.