high rates of morbidity and mortality; ease of dissemination and communicability; ability to cause a public panic; and special action required by public health officials to respond. Category A agents include anthrax, botulism, plague, smallpox, and viral hemorrhagic fevers. List of bio-agents of military importance The following pathogens and toxins were weaponized by one nation or another at some time. NATO abbreviations are included where applicable. Bacterial bio-agents Chlamydial bio-agents Rickettsial bio-agents Viral bio-agents Mycotic bio-agents Biological toxins Biological vectors Simulants Simulants are organisms or substances which mimic physical or biological properties of real biological agents, without being pathogenic. They are used to study the efficiency of various dissemination techniques or the risks caused by the use of biological agents in bioterrorism. To simulate dispersal, attachment or the penetration depth in human or animal lungs, simulants must have particle sizes, specific weight and surface properties, similar to the simulated biological agent. The typical size of simulants (1–5 µm) enables it to enter buildings with closed windows and doors and penetrate deep into the lungs. This bears a significant health risk, even if the biological agent is normally not pathogenic. Bacillus globigii (historically named Bacillus subtilis in the context of bio-agent simulants) (BG, BS, or U) Serratia marcescens (SM or P) Aspergillus fumigatus mutant C-2 (AF) Escherichia coli (EC) Bacillus thuringiensis (BT) Erwinia herbicola (current accepted name: Pantoea agglomerans) (EH) Fluorescent particles such as zinc cadmium sulfide, ZnCdS (FP) International law While the history of biological weapons use goes back more than six centuries to the siege of Caffa in 1346, international restrictions on biological weapons 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. Due to these reservations, it was in practice a "no-first-use" agreement only. The 1972 Biological Weapons Convention (BWC) supplements the Geneva Protocol by prohibiting the development, production, acquisition, transfer, stockpiling and use of biological weapons. Having entered into force on 26 March 1975, the BWC was the first multilateral disarmament treaty to ban the production of an entire category of weapons of mass destruction. As of March 2021, 183 states have become party to the treaty. The BWC is considered to have established a strong global norm against biological weapons, which is reflected in the treaty's