Short answers, pulled from the story.
Hittite texts from 1500 to 1200 BC record the earliest documented intent to use biological weapons. Victims of an unknown plague were driven into enemy lands to cause epidemics during this period.
Mongol warriors of the Golden Horde died of plague near Kaffa and their bodies were thrown over the walls of the besieged Crimean city. This operation may have spread the Black Death across Europe and North Africa, causing approximately 25 million Europeans to perish.
Lieutenant General Shirō Ishii commanded Unit 731, a secret Imperial Japanese Army unit based at Pingfang in Manchuria. This facility conducted fatal human experiments on prisoners to develop biological weapons.
The Biological Weapons Convention opened for signature on the 10th of April 1972 and entered into force on the 26th of March 1975. It became the first multilateral disarmament treaty to ban production of an entire category of weapons of mass destruction.
Biological weapons cost about 0.05 percent of conventional weapon costs to produce similar numbers of mass casualties per square kilometer. Common technology can be used to produce agents like those found in vaccine or food production facilities.