Before the 20th century, the use of biological agents took three major forms: Deliberate contamination of food and water with poisonous or contagious material Use of microbes, biological toxins, animals, or plants in a weapon system Use of biologically inoculated fabrics and personsIn the 20th century, sophisticated bacteriological and virological techniques allowed the production of significant stockpiles of weaponized bio-agents: Bacterial agents: Anthrax, Brucella, Tularemia, etc. Wikipedia