|Weapons of mass destruction|
A biological agent (also called bio-agent, biological threat agent, biological warfare agent, biological weapon, or bioweapon) is a bacterium, virus, protozoan, parasite, fungus, chemical, 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.
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.
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). 
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".
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.
|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)|
|Disease||Causative Agent (Military Symbol)|
|Psittacosis||Chlamydophila psittaci (SI)|
|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)|
|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)|
|Disease||Causative Agent (Military Symbol)|
|Coccidiomycosis||Coccidioides immitis (OC)|
|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|
|Vector (Military Symbol)||Disease|
|Mosquito ( Aedes aegypti ) (AP)||Malaria, Dengue fever, Chikungunya, Yellow fever, other Arboviruses|
|Oriental flea ( Xenopsylla cheopis )||Plague, Murine typhus|
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.
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. 
Biological warfare, also known as germ warfare, is the use of biological toxins or infectious agents such as bacteria, viruses, insects, and fungi with the intent to kill, harm or incapacitate humans, animals or plants as an act of war. Biological weapons are living organisms or replicating entities. Entomological (insect) warfare is a subtype of biological warfare.
The Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or other Gases, and of Bacteriological Methods of Warfare, usually called the Geneva Protocol, is a treaty prohibiting the use of chemical and biological weapons in international armed conflicts. It was signed at Geneva on 17 June 1925 and entered into force on 8 February 1928. It was registered in League of Nations Treaty Series on 7 September 1929. The Geneva Protocol is a protocol to the Convention for the Supervision of the International Trade in Arms and Ammunition and in Implements of War signed on the same date, and followed the Hague Conventions of 1899 and 1907.
A weapon of mass destruction (WMD) is a chemical, biological, radiological, nuclear, or any other weapon that can kill and bring significant harm to numerous individuals or cause great damage to artificial structures, natural structures, or the biosphere. The scope and usage of the term has evolved and been disputed, often signifying more politically than technically. Originally coined in reference to aerial bombing with chemical explosives during World War II, it has later come to refer to large-scale weaponry of warfare-related technologies, such as chemical, biological, radiological, or nuclear warfare.
The Biological Weapons Convention (BWC), or Biological and Toxin Weapons Convention (BTWC), is a disarmament treaty that effectively bans biological and toxin weapons by prohibiting their development, production, acquisition, transfer, stockpiling and use. The treaty's full name is the Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on their Destruction.
The United States biological weapons program officially began in spring 1943 on orders from U.S. President Franklin Roosevelt. Research continued following World War II as the U.S. built up a large stockpile of biological agents and weapons. Over the course of its 27-year history, the program weaponized and stockpiled the following seven bio-agents :
The Soviet Union covertly operated the world's largest, longest, and most sophisticated biological weapons program, thereby violating its obligations as a party to the 1972 Biological Weapons Convention. The program began in the 1920s and lasted until at least September 1992 but has possibly been continued by Russia after that.
The M143 bomblet was a biological cluster bomb sub-munition developed by the United States during the 1960s. The spherical bomblet was the biological version of the Sarin-filled M139 chemical bomblet.
The "Statement on Chemical and Biological Defense Policies and Programs" was a speech delivered on November 25, 1969, by U.S. President Richard Nixon. In the speech, Nixon announced the end of the U.S. offensive biological weapons program and reaffirmed a no-first-use policy for chemical weapons. The statement excluded toxins, herbicides and riot-control agents as they were not chemical and biological weapons, though herbicides and toxins were both later banned. The decision to ban biological weapons was influenced by a number of domestic and international issues.
Entomological warfare (EW) is a type of biological warfare that uses insects to interrupt supply lines by damaging crops, or to directly harm enemy combatants and civilian populations. There have been several programs which have attempted to institute this methodology; however, there has been limited application of entomological warfare against military or civilian targets, Japan being the only state known to have verifiably implemented the method against another state, namely the Chinese during World War II. However, EW was used more widely in antiquity, in order to repel sieges or cause economic harm to states. Research into EW was conducted during both World War II and the Cold War by numerous states such as the Soviet Union, United States, Germany and Canada. There have also been suggestions that it could be implemented by non-state actors in a form of bioterrorism. Under the Biological and Toxic Weapons Convention of 1972, use of insects to administer agents or toxins for hostile purposes is deemed to be against international law.
The Biological Weapons Anti-Terrorism Act of 1989 (BWATA), Pub.L. 101–298, enacted May 22, 1990) was a piece of U.S. legislation that was passed into law in 1990. It provided for the implementation of the Biological Weapons Convention as well as criminal penalties for violation of its provisions. The law was amended in 1996 and has been used to prosecute several individuals.
Horn Island Chemical Warfare Service Quarantine Station, also known as the Horn Island Testing Station, was a U.S. biological weapons testing site during World War II. It was located on Mississippi's Horn Island and opened in 1943. When the war ended, the facility was closed.
VEREX was an ad hoc committee assembled in 1991 by the Third Review Conference of the Biological Weapons Convention (BWC) to research verification measures to enforce the BWC from a scientific and technical standpoint.
The general-purpose criterion is an important concept in international law that broadly governs international agreements with respect to, for instance biological and chemical weapons. Although the term is not found within such agreements, it is "regularly used" to describe the comprehensive nature of prohibitions regarding all biological and chemical weapons.
The United States biological defense program—in recent years also called the National Biodefense Strategy—refers to the collective effort by all levels of government, along with private enterprise and other stakeholders, in the United States to carry out biodefense activities.
New physical principles weapons are a wide range of weapons or systems created using emerging technologies, like wave, psychophysical, and genetic weapons.
Anthrax weaponization is the development and deployment of the bacterium Bacillus anthracis or, more commonly, its spore, as a biological weapon. As a biological weapon, anthrax has been used in biowarfare and bioterrorism since 1914. However, in 1975 the Biological Weapons Convention prohibited the "development, production and stockpiling" of biological weapons. It has since been used in bioterrorism.
The United Nations Secretary-General’s Mechanism for Investigation of Alleged Use of Chemical and Biological Weapons (UNSGM), is a tool that allows the Secretary-General to investigate alleged uses of biological or chemical weapons. The UNSGM is not a standing investigative body, but instead relies on a member state-provided list of qualified experts, consultants, and analytical laboratories that may be activated on short notice to support UNSGM investigations.