Category A Infectious Microorganisms

 A category A substance (pathogen or agent) is “an infectious substance which is transported in a form that, when exposure to it occurs, is capable of causing permanent disability or life-threatening or fatal disease to otherwise healthy humans or animals.” Deciding if an infectious substance is a Category A substance is relatively easy because there are relatively few Category A substances and because Category A substances are specifically designated and listed by IATA and DOT. The list of Category A substances is not all-inclusive, and a thorough risk assessment must be performed before assigning a substance to Category A. 

UN Numbers of Category A Pathogens

Category A pathogens and substances likely to contain Category A pathogens must be assigned the UN number UN2814 (proper shipping name: Infectious Substance, Affecting Humans) or UN2900 (proper shipping name: Infectious Substance, Affecting Animals). If a Category A pathogen/substance is capable of causing disease in both humans and animals, the pathogen/substance must be shipped as a Category A substance affecting humans (UN2814). 

Examples of infectious substances included in Category A

Bacillus anthracis

Bacillus anthracis is the etiological agent of anthrax. Bacillus anthracis was intentionally released into the US postal system in October 2001. In this bio-terrorism-related event, various individuals got a letter containing a written note that the person opening the letter had been exposed to spores of Bacillus anthracis. Cultures of Bacillus anthracis are labeled as Category A infectious agents.


The culture of three Brucella species, Brucella abortus, Brucella melitensis, and Brucella suis are labeled as Category A infectious agents. Brucella species causes brucellosis (undulant fever). People acquire this zoonotic disease from infected cattle (Brucella abortus), goats and sheep (Brucella melitensis), and pigs (Brucella suis) by ingesting contaminated milk products or through direct contact in occupational settings such as an abattoir.

Other organisms

  1. Burkholderia mallei (cultures only)
  2. Burkholderia pseudomallei (cultures only)
  3. Chalamydia psittaci (avian) (cultures only)
  4. Clostridium botulinum (cultures only)
  5. Coccidioides immitis (cultures only)
  6. Coxiella burnetii (cultures only)
  7. Crimean-Congo hemorrhagic fever virus
  8. Dengue virus (cultures only)
  9. Eastern equine encephalitis virus (culture only)
  10. Escherichia coli, verotoxigenic (cultures only)
  11. Ebola virus
  12. Francisella tularensis (cultures only)
  13. Hantavirus causing hemorrhagic fever with renal syndrome
  14. Hepatitis B virus (cultures only)
  15. Herpes B virus (cultures only)
  16. Human Immunodeficiency Virus (cultures only)
  17. Lassa virus
  18. Marburg virus
  19. Monkeypox virus
  20. Mycobacterium tuberculosis (cultures only)
  21. Poliovirus virus (cultures only)
  22. Rabies virus (cultures only)
  23. Rickettsia rickettsii (cultures only)
  24. Rift Valley fever virus (cultures only)
  25. Shigella dysenteriae type 1 (cultures only)
  26. Variola virus
  27. Venezuelan equine encephalitis virus (cultures only)
  28. West Nile virus (cultures only)
  29. Yellow fever virus (cultures only)
  30. Yersinia pestis (cultures only)
  31. Classical swine fever virus (cultures only)
  32. Foot and mouth disease virus (cultures only)
  33. Goat pox virus (cultures only)
  34. Lumpy skin disease virus (cultures only)
  35. Newcastle disease virus (cultures only)
  36. Sheep pox virus (cultures only)
  37. Swine vesicular disease virus (cultures only)
  38. Vesicular stomatitis virus (cultures only)

Source: American Society for Microbiology


  1. Darling, R. G., Catlett, C. L., Huebner, K. D., & Jarrett, D. G. (2002). Threats in bioterrorism. I: CDC category A agents. Emergency medicine clinics of North America, 20(2), 273–309.
  2. He, Y., Rush, H. G., Liepman, R. S., Xiang, Z., & Colby, L. A. (2007). Pathobiology and management of laboratory rodents administered CDC category A agents. Comparative medicine, 57(1), 18–32.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

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