The most devastating Plague in human history was that of 1348, called the black death, swept out half of the world's population. It was due largely to unhygienic conditions, being transmitted by rats flea. Smallpox virus and the invention of vaccination by Edward Jenner. Malaria, each year more than four thousand people die of it, mainly in sub-Saharan Africa. Tuberculosis, the most lethal disease in human history, continues to kill one-two million people each year. All over the world, two billion infected by it. Since the '40s, starting with the discovery of Alexander Fleming, antibiotics became the main solution to fight the bacterial agent. Typhus, caused by the transmission of bacteria due to poor hygienic conditions, propagated during several wars between 1812 (Russian campaign of Napoleon) and 1922 (Russian civil war). Cholera, in the last two centuries, claimed the lives of 50 million people all around the world. Despite being curable, every year it infects 4 million and kills a hundred people. This disease enters the body via contaminated food and water. The seven pandemics that occurred in 1817 originated from the Gange river in India, brought in Asia and Europe by millions of peregrines who crowd its shore periodically to celebrate the local religious festival. In the '30s of the past century, it spread mainly into the metropolis like Paris and London, overcrowded and with poor hygiene.
Influenza, the worst epidemic in terms of mortality and rapidity of diffusion, with an estimate of fifty million people killed from 1918 to 1919. Polio, a virus that hit children under ten, cause disabilities for twenty million people, killing one million. In the '50s, a vaccine was finally developed, defining ultimately this disease. HIV-AIDS virus, 40 million victims since its discovery in 1981, every year it kills a million people, actually, together with TB, it's the most lethal infection.