biological agent biological agent a biological agent (also called bio-agent, biological threat agent, biological warfare agent, biological weapon, or bioweapon) is a bacterium, virus, protozoan, parasite, fungus, or toxin that can be used purposefully as a weapon in bioterrorism or biological warfare (bw). in addition to these living or replicating pathogens, toxins and biotoxins are also included among the bio-agents. more than 1,200 different kinds of potentially weaponizable bio-agents have been described and studied to date. this article is about harmful biological agents. for therapeutic biological drugs, see biopharmaceutical. weapons of mass destruction by type biological chemical nuclear radiological by country albania algeria argentina australia brazil bulgaria canada china egypt france germany india iran iraq israel italy japan libya mexico myanmar netherlands north korea pakistan philippines poland rhodesia romania russia (soviet union) saudi arabia south africa south korea sweden switzerland syria taiwan ukraine united kingdom united states proliferation chemical nuclear missiles treaties list of treaties (treaty parties) category a culture of bacillus anthracis, the causative agent of anthrax some biological agents have the ability to adversely affect human health in a variety of ways, ranging from relatively mild allergic reactions to serious medical conditions, including serious injury, as well as serious or permanent disability or even death. many of these organisms are ubiquitous in the natural environment where they are found in water, soil, plants, or animals. bio-agents may be amenable to "weaponization" to render them easier to deploy or disseminate. genetic modification may enhance their incapacitating or lethal properties, or render them impervious to conventional treatments or preventives. since many bio-agents reproduce rapidly and require minimal resources for propagation, they are also a potential danger in a wide variety of occupational settings. the 1972 biological weapons convention (bwc) is an international treaty banning the development, use or stockpiling of biological weapons; as of march 2021, there were 183 states parties to the bwc. bio-agents are, however, widely studied for both defensive and medical research purposes under various biosafety levels and within biocontainment facilities throughout the world. classifications operational the former us biological warfare program (1943–1969) categorized its weaponized anti-personnel bio-agents as either "lethal agents" (bacillus anthracis, francisella tularensis, botulinum toxin) or "incapacitating agents" (brucella suis, coxiella burnetii, venezuelan equine encephalitis virus, staphylococcal enterotoxin b). legal since 1997, united states law has declared a list of bio-agents designated by the u.s. department of health and human services or the u.s. department of agriculture that have the "potential to pose a severe threat to public health and safety" to be officially defined as "select agents" and possession or transportation of them are tightly controlled as such. select agents are divided into "hhs select agents and toxins", "usda select agents and toxins" and "overlap select agents and toxins". regulatory the u.s. centers for disease control and prevention (cdc) breaks biological agents into three categories: category a, category b, and category c. category a agents pose the greatest threat to the u.s. criteria for being a category "a" agent include 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 disease causative agent (military symbol) anthrax bacillus anthracis (n or tr) brucellosis (bovine) brucella abortus brucellosis (caprine) brucella melitensis (am or bx) brucellosis (porcine) brucella suis (us, ab or nx) cholera vibrio cholerae (ho) diphtheria corynebacterium diphtheriae (dk) dysentery (bacterial) shigella dysenteriae, escherichia coli (y) glanders burkholderia mallei (la) listeriosis listeria monocytogenes (tq) melioidosis burkholderia pseudomallei (hi) plague yersinia pestis (le) tularemia francisella tularensis (sr or jt) chlamydial bio-agents disease causative agent (military symbol) psittacosis chlamydophila psittaci (si) rickettsial bio-agents disease causative agent (military symbol) q fever coxiella burnetii (ou) rocky mountain spotted fever rickettsia rickettsii (ri or uy) typhus (human) rickettsia prowazekii (ye) typhus (murine) rickettsia typhi (av) viral bio-agents disease causative agent (military symbol) comments equine encephalitis (eastern) eastern equine encephalitis virus (zx) equine encephalitis (venezuelan) venezuelan equine encephalomyelitis virus (fx) equine encephalitis (western) western equine encephalitis virus (ev) japanese b encephalitis japanese encephalitis virus (an) marburg hemorrhagic fever (marburg hf) marburg virus (marv) by the soviet union rift valley fever rift valley fever virus (fa) smallpox variola virus (zl) yellow fever yellow fever virus (oj or lu) mycotic bio-agents disease causative agent (military symbol) coccidiomycosis coccidioides immitis (oc) biological toxins toxin source of toxin (military symbol) abrin rosary pea (abrus precatorius) botulinum toxins (a through g) clostridium botulinum bacteria or spores, and several other clostridial species. (x or xr) ricin castor bean (ricinus communis) (w or wa) saxitoxin various marine and brackish cyanobacteria, such as anabaena, aphanizomenon, lyngbya, and cylindrospermopsis (tz) staphyloccocal enterotoxin b staphylococcus aureus (uc or pg) tetrodotoxin various marine bacteria, including vibrio alginolyticus, pseudoalteromonas tetraodonis (pp) trichothecene mycotoxins various species of fungi, including fusarium, trichoderma, and stachybotrys biological vectors vector (military symbol) disease mosquito (aedes aegypti) (ap) malaria, dengue fever, chikungunya, yellow fever, other arboviruses oriental flea (xenopsylla cheopis) plague, murine typhus 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 the biological weapons convention 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 preamble, stating that the use of biological weapons would be "repugnant to the conscience of mankind". however, the bwc's effectiveness has been limited due to insufficient institutional support and the absence of any formal verification regime to monitor compliance. in 1985, the australia group was established, a multilateral export control regime of 43 countries aiming to prevent the proliferation of chemical and biological weapons. in 2004, the united nations security council passed resolution 1540, which obligates all un member states to develop and enforce appropriate legal and regulatory measures against the proliferation of chemical, biological, radiological, and nuclear weapons and their means of delivery, in particular, to prevent the spread of weapons of mass destruction to non-state actors.