Background: Bacillus anthracis as a Biological Agent

 

 

Author: Manisha Samy

 

Bacillus anthracis is a large, Gram-positive, spore-forming bacterium (Todar). It was the first bacterium shown to have been a disease-causing agent in 1877 by Robert Koch who grew the organism and demonstrated its ability to form endospores causing anthrax when injected into animal models (Todar). Anthrax is a zoonotic disease caused by B. anthracis most commonly in wild and domestic mammals such as cattle and sheep (Wright). There are three forms of anthrax dependent on route of B. anthracis exposure: cutaneous, gastrointestinal, or inhalation. Exposure occurs through inhalation and ingestion of spores produced by the bacterium which happen to be highly resistant to heat, cold, drought, UV light, and gamma radiation (Wright). Perhaps it is for their resilient nature that the Center for Disease Control (CDC) have classified B. anthracis spores as a category A biological warfare agent.

 The first vaccine against anthrax was developed for livestock in 1880 (Wright). Agricultural and industrial workers are most commonly affected by naturally-forming anthrax. The exact infectious dose of B. anthracis is unknown for humans, but it is believed that a small number of spore exposures is enough for anthrax diagnosis (Wright).  Further studies need to be done in order to narrow down the lethal dose in humans; however, such studies prove to be difficult. Because B. Anthracis spores can remain viable in soli for over a decade, this provides a means for exposure to grazing cattle and sheep. In this manner agricultural workers who come in contact with contaminated animal products or an infected animal can acquire anthrax. Known industrial cases of anthrax result from cutaneous inoculation and/or inhalation of particles containing B. anthracis (Wright). South America, Central America, southern and eastern Europe, Asia, Africa, the Caribbean, and the Middle East are all enzootic regions where naturally occurring anthrax is shown (Wright). This is most likely due to inadequate control programs for anthrax in livestock. Even with proper personal protective equipment (PPE), workers still can encounter contaminated products because PPE is not 100% effective. In the US, naturally occurring anthrax cases have decreased since the middle of the 20^th century from 25 to 8 states reporting incidents from 1996-2006 (Wright). I believe that this is largely due to greater efforts in countermeasures and importance given to biosurveillance. 

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Todar, Kenneth. "Bacillus Anthracis and Anthrax." Bacillus Anthracis and Anthrax. Todar's OnlineTextbook of Bacteriology, n.d. Web. May-June 2013. <http://textbookofbacteriology.net/Anthrax.html>.

Wright, Jennifer G., and Conrad P. Quinn. "Use of Anthrax Vaccine in the United States Rcommendations of the Advisory Committee on Immunization Practices (ACIP), 2009." Morbidity and Mortality Weekly Report 59.RR-6 (2009): n. pag. Print.