Types of agents




Under current United States law, bio-agents which have been declared by the U.S. Department of Health and Human Services or the U.S. Department of Agriculture to have the "potential to pose a severe threat to public health and safety" are officially defined as "select agents." The CDC categorizes these agents (A, B or C) and administers the Select Agent Program, which regulates the laboratories which may possess, use, or transfer select agents within the United States. As with US attempts to categorize harmful recreational drugs, designer viruses are not yet categorized and avian H5N1 has been shown to achieve high mortality and human-communication in a laboratory setting.

Category Aedit

These high-priority agents pose a risk to national security, can be easily transmitted and disseminated, result in high mortality, have potential major public health impact, may cause public panic, or require special action for public health preparedness.

  • Tularemia or "rabbit fever": Tularemia has a very low fatality rate if treated, but can severely incapacitate. The disease is caused by the Francisella tularensis bacterium, and can be contracted through contact with fur, inhalation, ingestion of contaminated water or insect bites. Francisella tularensis is very infectious. A small number of organisms (10–50 or so) can cause disease. If F. tularensis were used as a weapon, the bacteria would likely be made airborne for exposure by inhalation. People who inhale an infectious aerosol would generally experience severe respiratory illness, including life-threatening pneumonia and systemic infection, if they are not treated. The bacteria that cause tularemia occur widely in nature and could be isolated and grown in quantity in a laboratory, although manufacturing an effective aerosol weapon would require considerable sophistication.
  • Anthrax: Anthrax is a non-contagious disease caused by the spore-forming bacterium Bacillus anthracis. The ability of Anthrax to produce within small spores, or bacilli bacterium, makes it readily permeable to porous skin and can cause abrupt symptoms within 24 hours of exposure. The dispersal of this pathogen among densely populated areas is said to carry less than one percent mortality rate, for cutaneous exposure, to a ninety percent or higher mortality for untreated inhalational infections. An anthrax vaccine does exist but requires many injections for stable use. When discovered early, anthrax can be cured by administering antibiotics (such as ciprofloxacin). Its first modern incidence in biological warfare were when Scandinavian "freedom fighters" supplied by the German General Staff used anthrax with unknown results against the Imperial Russian Army in Finland in 1916. In 1993, the Aum Shinrikyo used anthrax in an unsuccessful attempt in Tokyo with zero fatalities. Anthrax was used in a series of attacks by a microbiologist at the US Army Medical Research Institute of Infection Disease on the offices of several United States Senators in late 2001. The anthrax was in a powder form and it was delivered by the mail. This bioterrorist attack inevitably prompted seven cases of cutaneous anthrax and eleven cases of inhalation anthrax, with five leading to deaths. Additionally, an estimated 10 to 26 cases had prevented fatality through treatment supplied to over 30,000 individuals. Anthrax is one of the few biological agents that federal employees have been vaccinated for. In the US an anthrax vaccine, Anthrax Vaccine Adsorbed (AVA) exists and requires five injections for stable use. Other anthrax vaccines also exist. The strain used in the 2001 anthrax attacks was identical to the strain used by the USAMRIID.
  • Smallpox: Smallpox is a highly contagious virus. It is transmitted easily through the atmosphere and has a high mortality rate (20–40%). Smallpox was eradicated in the world in the 1970s, thanks to a worldwide vaccination program. However, some virus samples are still available in Russian and American laboratories. Some believe that after the collapse of the Soviet Union, cultures of smallpox have become available in other countries. Although people born pre-1970 will have been vaccinated for smallpox under the WHO program, the effectiveness of vaccination is limited since the vaccine provides high level of immunity for only 3 to 5 years. Revaccination's protection lasts longer. As a biological weapon smallpox is dangerous because of the highly contagious nature of both the infected and their pox. Also, the infrequency with which vaccines are administered among the general population since the eradication of the disease would leave most people unprotected in the event of an outbreak. Smallpox occurs only in humans, and has no external hosts or vectors.
  • Botulinum toxin: The neurotoxin Botulinum is the deadliest toxin known to man, and is produced by the bacterium Clostridium botulinum. Botulism causes death by respiratory failure and paralysis. Furthermore, the toxin is readily available worldwide due to its cosmetic applications in injections.
  • Bubonic plague: Plague is a disease caused by the Yersinia pestis bacterium. Rodents are the normal host of plague, and the disease is transmitted to humans by flea bites and occasionally by aerosol in the form of pneumonic plague. The disease has a history of use in biological warfare dating back many centuries, and is considered a threat due to its ease of culture and ability to remain in circulation among local rodents for a long period of time. The weaponized threat comes mainly in the form of pneumonic plague (infection by inhalation) It was the disease that caused the Black Death in Medieval Europe.
  • Viral hemorrhagic fevers: This includes hemorrhagic fevers caused by members of the family Filoviridae (Marburg virus and Ebola virus), and by the family Arenaviridae (for example Lassa virus and Machupo virus). Ebola virus disease, in particular, has caused high fatality rates ranging from 25–90% with a 50% average. No cure currently exists, although vaccines are in development. The Soviet Union investigated the use of filoviruses for biological warfare, and the Aum Shinrikyo group unsuccessfully attempted to obtain cultures of Ebola virus. Death from Ebola virus disease is commonly due to multiple organ failure and hypovolemic shock. Marburg virus was first discovered in Marburg, Germany. No treatments currently exist aside from supportive care. The arenaviruses have a somewhat reduced case-fatality rate compared to disease caused by filoviruses, but are more widely distributed, chiefly in central Africa and South America.

Category Bedit

Category B agents are moderately easy to disseminate and have low mortality rates.

  • Brucellosis (Brucella species)
  • Epsilon toxin of Clostridium perfringens
  • Food safety threats (for example, Salmonella species, E coli O157:H7, Shigella, Staphylococcus aureus)
  • Glanders (Burkholderia mallei)
  • Melioidosis (Burkholderia pseudomallei)
  • Psittacosis (Chlamydia psittaci)
  • Q fever (Coxiella burnetii)
  • Ricin toxin from Ricinus communis (castor beans)
  • Abrin toxin from Abrus precatorius (Rosary peas)
  • Staphylococcal enterotoxin B
  • Typhus (Rickettsia prowazekii)
  • Viral encephalitis (alphaviruses, for example,: Venezuelan equine encephalitis, eastern equine encephalitis, western equine encephalitis)
  • Water supply threats (for example, Vibrio cholerae, Cryptosporidium parvum)

Category Cedit

Category C agents are emerging pathogens that might be engineered for mass dissemination because of their availability, ease of production and dissemination, high mortality rate, or ability to cause a major health impact.

  • Nipah virus
  • Hantavirus

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