good wiki

Biological Weapons Convention

While the history of biological warfare goes back more than six centuries to the Siege of Caffa in 1346 CE, international restrictions on biological warfare began only with the 1925 Geneva Protocol, which prohibits the use but not the possession or development of chemical and biological weapons. Upon ratification of the Geneva Protocol, several countries made reservations regarding its applicability and use in retaliation.

More at Wikipedia

About